I live in a post war council house since 1987. It wasnt until they filled the cavity with insulation 25 years ago did i start getting black mould patches. Can't say the house feels any warmer with it either. Just more damp & condensation.
It would have been better to have left it alone.Our house when it was build they put like blanket stuff in the cavity.I must admit it never caused any damp at over 40 years.
Bit of extra history I discovered as a building surveyor: large air bricks were often placed above the DPC level to ventilate larders or pantries in houses built before the widespread use of fridges. You can normally identify these 1. Where they directly align with a large larder or pantry and 2. If it was on the north most facing side of the house out of direct sun light. Roger is right most of these ‘wall airbricks’ are to ventilate a room though.
my Mum had a "pantry" under the stairs before the advent of electric fridges, comprising of a zink screen in front of an air brick and food sat on a marble slab, one tuesday she had a nasty shock and chucked half a joint of beef crawling with maggotts and blueflies, that was dinner, bastards.
I think I might have one of these - no larder (anymore), but it opens up into the kitchen. Would you say these are no longer needed? It's letting in a huge draft.
@@dagmarbelesova4284 Depends on your current kitchen set up really mate. Kitchens do require good ventilation as a lot more moisture than people think is produced from cooking, tumble driers and boiling kettles etc. If you use other means of ventilation such as extractor hoods, a mechanical extractor fan or are just generally good at opening windows and heating your house well then yes you could probably loose the airbricks. If don’t utilise any of these ventilation methods then there is nothing stopping you from temporarily covering the airbricks and then buying a cheap humidistat off amazon to monitor for high humidity in the kitchen and also performing visual checks for mould/condensation patches before deciding whether to remove them. Hope that helps!
@Fraser-B Thank you for the quick and comprehensive reply, that's super helpful! I've noticed the windows misting up so I always open them and use the extractor when doing anything in the kitchen. I think thr utility of the vent is limited now anyway as it's hidden behind the kitchen cupboard. I might consider an extra tor fan or a single room MHRV, the vent just doesn't seem like a great solution atm as it can't be closed or controlled in any way.
We purchased a mid eighties house late summer with solid concrete floors, cavity walls and air bricks above the DPC. Some minor damp issues on survey that surveyor advised was probably due to poor ventilation? Come the winter the damp became worse and we had problems with wood lice crawling around ground floor. Next summer we had air bricks removed, guess what come the winter? No damp issues and no wood lice.
When I was an apprentice, regs were just introducing insulation into 50mm cavities! My mentor always moaned about it bridging the cavity and reducing air circulation and the batts making rags on the ties causing damp. The price per 1000 didn't go up though, I think that was his main gripe!
I was always stunned by the sheer simplicity of cavity wall insulation sales folk. They'd knock on my door and ask if I want it, I'd tell them it's a Victorian house - with solid brick walls. They'd say 'oh'... and then go next door, and enxt door to that etc. In a terrace of houses exactly the same, getting the same answer each time. They have now moved onto the highly toxic and flamable external insulation. So they're having to be told what a conservation area is by everyone that answers.
I'm in a conservation area and I'm having external wall insulation. It was approved with no conditions by the council. It would only be if the parish council are staunch traditionalists or if the house is listed that you might have any issue.
It would only take one, probably elderly, houseowner, who doesn't know/understand they have single skin walls, to say yes. Then they could turn up, drill a few holes in the walls, make some noise and pack up.
@@peterthebricky Just looked one up, has Class E fire rating, which means it is combustable and has a high contributes to the fire. Edit; The class E was a polystyrene based one. I can see Kingspan have some class C and Rockwool has an A1 - so if you are getting external insulation, go for something that seems fireproof like Rockwool.
Here in Australia the top of the cavity and the cavity itself are left open to vent the cooler under floor air. This keeps the house cooler in summer and keeps the underfloor drier.
Hi Roger, At Last...!!! It took me forever to find a video on cavities. It seems everyone talks about window reveals and door reveals, but you are the first I can find to talk about the top of the cavity. Thank you for clearing this up. There is not much information on the top (eaves) of the cavity and how it should be sealed. Also it seems that not many of the eaves I have seen on older houses seem to be sealed in the construction. Maybe an oversight or just lazy builders. Thanks Roger and the Skill Builder team...
My 1911 terrace has lime mortared cavity brick walls. The cavity is ventillated externally by huge cast iron vents a the top and bottom, plus gaps into the cavity above all the sash window frames. After 100+ years the walls are beautifully stright with apparently no issues with corrosion of the wall ties, but I hate to think what could happen if I messed with the cavity ventilation in any way.
I'd suggest it would be worth filling the gaps on the inner skin around the windows as the gaps will allow moist internal air into the cavity. You may be lucky in any case, and have wall ties that don't rust (wrought iron lasts for decades even right by the sea and regularly submerged in saltwater, and I think some early types of tie were even brick-based). I'm not against changes and improvements myself. My own house has a 9" solid exterrior wall, which isn't its worst feature, but the wall does get cold in the winter and hot in the summer and is pretty awful thermally. I think the problem we have is people rushing into a one-size-fits-all approach, often by inexperienced installers and without consulting people with a thorough understanding of how historic buildings work. I did insulate my suspended timber ground floor, and found it to be a significant improvement on an uninsulated one, but I can see how this could easily be done wrong and also cause trouble.
Could you present a video series designing/managing/building a house built to your best standards. The idealistically built home. Include everything from purchase to plans to permission, consultations with trades. Link videos to why that x is best practice. How much it would cost a normal joe. Could even get a building merchant to sponsor it. Cheers.
Okay... I am an Engineer (old school), who is in the later stages of building a timber frame passive house. I have a rendered block outer leaf with 50mm cavity. the timber frame has a semi permeable foil/fabric layer onto 9mm OSB sheathing, which in turn nailed to 235mm inner leaf timber stud work. The top of the cavity wall is closed off with fire socks. The semi permeable membrane works on an "Osmosis" method where it allows residual moisture content in the frame to escape into the cavity. If that cavity is fully closed and saturated with moisture, like after having heavy driving rain then sun heating the wall, creating high humidity, this effect will be diminished. Also by having cavity trays at DPC level and above Lintels, there are weep vents at 900mm intervals, so there will be air movement to a degree. The fire socks around the roof line will stop air to the attic space, and also fire if it does happen. I believe that having a closed off cavity will eventually impact on the timber frame in the future. Because of my fears, probably unfounded, I will be painting the render with ProPerla paint when the weather warms up. Apparently, hydrophobic paint is the way to go nowadays.
@adamsweet3587 could you not install a soffit/fascia vent so any moisture goes outside and you maintain the firestop..? I would also paint the render...
How does cavity 'saturate' with moisture after heavy rain? What is the point of building an external wall if this occurs - bricks absorb / pass water through VERY slowly so unless under water or direct heavy rain for weeks and weeks, its not going to happen! If you are building with an internal breathable skin then that MUST be ventilated on its outer face - the design is not correct if not, you are mixing methods and not in a good way!
As long as you're weep vents are 65mm high and you have them at 900 centres above and below any fire socks and at dpc level at the ground, this should be sufficient to properly vent the cavity. Here in Scotland for timber frame construction, the regs require cavity vents of at least 300mm2 every 1200mm. You should get more than that if your vents are at 900 centres.
@@kawazukisoddbits2717 If you have a closed cavity and have a damp inner side of the outer leaf, and after a period of driven rain, the eventual sun will initial warm that wall to create a more humid environment, until the wall outside dries, to then pull back the moisture to the outside. The levels here maybe very small and will not affect the inner leaf and I am probably being overly too critical. Traditionally cavities were open at the top and roof eaves had ventilation either in the soffits or as vent bars sitting on top of the fascia boards(which the tile sat on), so you had a vented loft space. My house is on a hill (in Cornwall), exposed, South facing, and the South West weather fronts do push hard on my facing walls.
@@WilliamBell-tj9sq Yes, I do have weep vents at DPC and Lintel levels, so when my exposed house experiences high winds, which it does, it will force air from the exposed side around to the other side which will be at lower air pressure. I am probably being overly critical of my situation.
Housing designed with vented cavities ( 1920s,30, 40, 50, ) are best left vented. The cavities are open at wall plates for ventilation of roof timbers and timber floors. This method of construction was practical, to prevent dry rot.
Have you been living under a rock for the past 30 odd yrs? Fully filled cavities have been used and APPROVED for use in this time! Bad workmanship is the cause of damp penetration!
@ It is like putting a sponge inside the cavity retaining moisture . It bridges the cavity and draws water across the dry interior skin. It also promotes corrosion of the wall ties. Unless the exterior face of the wall is sealed with a properly sealed foil and reasonable gap maintained water will track across. It is such a stupid idea approved by officials that have had a mind fart. It has never been legal in my country. We frankly still have our brains turned on.
@ It cannot work, you are putting a sponge inside the cavity and tracking moisture to the dry skin. You are also jeopardising the structural integrity of the building by creating a moisture soak at every wall tie encouraging them to corrode. It could work with foil faced insulation but a cavity should still be maintained. Whoever approved that 30 years ago was having a brain fart. It’s not legal where I come from we still have our brains turned on. Seriously it is absolutely nuts, and fixing it with a paint on sealant is bs too. It’s poor building practice.
@davidconnolly7346 not arguing but where are you from. I'm in essex UK, I've laid bricks since 1986 with full fill insulation in 95% of the cavity work. I've yet to have a comeback. Modern full fill bats are water repellent but the older stuff not so much
The primary role of the cavity is to waterproof the building not provide a location for insulation. A way better method if you want additional insulation is brick veneer with the insulation within the interior timber wall. We leave our cavities open in Australia. We get so 3:04 much rainfall too. Cavities get a lot of water inside them, they also need ventilation to dry them out. It’s been working for 100’s of years. What do you do in England when all the wall ties corrode due to all the moisture trapped inside the cavity, condemn the building?
In a brick/block built building with a cavity that is fully sealed, how does moisture from driving rain seeping into the cavity escape? If the cavity warms up and has moisture, shouldn't there be somewhere for the moisture to go? Could a fully sealed cavity with no air flow cause dry rot? Does 'Rockwool' style cavity insulation allow air flow when the cavity is fully filled with it? Does it soak up and hold moisture or does it transfer it to the internal skin? These are the discussions I have on site consistently over the years and everyone has a different view. Personally, as a Bricklayer, I never seal the cavity at the top, I don't insert air bricks to the cavity and I prefer to use Rockwool type insulation when I can. I've never experienced any issues but I still don't know if that's the right way to go or not after more than 40 years on the trowel.
If rain is seeping into the cavity, the cavity is not fully sealed. A fully sealed cavity does not even let air in, much less water. If water can seep in, it can also evaporate through the same opening. Or weep holes at the bottom of the cavity. Now a fully sealed cavity might get a bit of water soaking *through* the external brick. But that's going to be very little, only in huge driving rain storms. And will evaporate quickly when the rain stops because there's very little of it. The water vapor will slowly move through and out of the brick. I've never seen it cause rot. Rockwool's main function it to prevent moving air. It's hydrophobic but even hydrophobic structures can be soaked with enough water. It will quickly drain, but it absolutely can be soaked. Hydrophobic just means it won't wick water into itself. So a few drops will sit on its surface. But running water will soak it. Sounds like what you're doing is having an open cavity filled with rockwool. So the rockwool prevents drafts, moving air. Can get soaked, but because it's open it will also dry out quickly. Perfect example why rockwool became popular. It's easier to stuff an accidentally or intentionally open cavity with it. Than to make sure the cavity traps air.
what happens in central Europe with driving rain? We do not have any cavity. Majority of houses are built from thick clay blocks of 440 mm thickness with many compartments in them holding the air / insulator/ or polystyrene beads or rockwool for isolation. No problem with dampness or thermal bridging and rain is no problem also,
It seems that some people confuse ventilation, draining and breathability. In the east of England where i now live most buildings up to 1960 are built with solid walls because it's a dry 2:49 climate and the bricks were low poroucitty with lime mortar; hence no need for cavities. There's no point allowing wet cold air to circulate against the internal skin which is transmitting moisture from the inside thus causing condensation which shows as damp on the bottom of the inside wall.
I have a 1928 built detached house with a cavity. The parlour was built with a suspended floor. There are air bricks front and rear, wind blows right through. However, the cavity has openings below floor level so wind blows up the unfilled cavity. There are air bricks level with the top of the 1st floor windows, these are unsleeved with cast iron sliding vents. The cavity is open at loft level. Effectively I have a single skin house as the walls are cooled (but dry) by cold wind blowing through. The walls inside are really cold. I have a lot to sort out!
You place sounds similar to mine, built around 1930 for heating with coal fires that no longer exist, but with a howling wind blowing underneath sucking out all the heat! The cavities were filled with insulation in the past but it leaks out everywhere. Some way to stop the wind blasting under but still allow circulation and removal of moist air is something I'd love to find. I've often imagined a heat pump or heat recovery system being fitted under there to provide a kind of underfloor heating, unfortunately never heard of such a thing being available! 🤷♀️
I'm in the process of liberating my airbricks. The house started with 5 in 1880. Two buried under paving. Two rendered over. And one had an extension built over it. I just don't understand why people look at things like that and assume they were put there without good reason.
Last 2 months i build an extension on my house. I filled our cavity with insulation about 3 years ago, so i was a bit nervous how it looked on the inside after removing some walls (in cold and rainy weather). You dont know how it goes in the cavity, maybe it is a bit wet or dampy or moldy. But it was a perfectly fine, dry insulation, dry bricks, no heaps of insulation flocking together etc. I have to say we do ventilate alot in house and the house is build in 1970, so the bricks and joints are good. I do think if you have a house with bricks and joint that are more porous or broken, you better re do the joins and impregnate the bricks before adding insulation.
With a cavity you get heat transfer from radiation + convection. Ideally you want to stop the air moving in the cavity without incurring additional heat loss via conduction.
At 0:48 why is that airbrick slightly below ground level? Rain water is going to run into that airbrick, an airbrick designed to remove damp is letting it pour in.
Because the owners have allowed the outside ground level to be raised above the damp proof course which will be immediately below the base of the air brick. The ground level, whether solid as shown in this case or just dirt, should be maintained as required by building regulations to be a minimum of two brick courses below dpc level. Ignorance is what has brought this about and a recipe for a future disaster.
Up untill the early 70s with the advent of cavity insulation all cavities were sealed at roof level and all air bricks wether pantry or floor insulation were chanelled through the cavity with propriety clay sleaves or slate, since cavity insulation appeared cavity insulation has to meet the roof insulation to avoid cold bridging so sealing cavities is a thing of the past.
My parents house built in 1960 has ventilated cavities and under floor space, and has no weep drains or cavity sills so the cavities have to be ventilated otherwise the footings will get wet with the moisture running down. It is a detached property, and when the outside temperature drops below zero C the heating has to be run 24 hours a day to stop the house getting cold. It can't have cavity wall insulation installed, there is too much very random stone in the front and back walls and also due to the issues with no cavity sills at the bottom.
My house built in 1987 has cavity wall insulation and no air bricks. The cavities are open in the loft, but they do not connect to the loft insulation there is at least 150mm all around the edge with no insulation. This is clearly not an accident, they don't connect anywhere. Also the roof line is low so the outer skin of the walls is about two bricks short of reaching ceiling level, so it would be extremely difficult to connect the two sets of insulation. If you did the soffit vents for the loft space would be blocked, hence why it is clear this is part of the design and not a mistake.
They want a house like an envelope of insulation and air thight so the only air coming in is through the air vents not leaking everywhere ... I use the extraterm full cavity fill with the plastic front and it leaves 10mm air gap on the eternal block... and keep the internal leaf thight against it.. I don't like to see people pumping these cavitys especially brick cavitys as they are so porous
Question I live in a 7-storey block of flats, ground floor. Traditional brick construction. Humid coastal Dorset. Outside walls have ventilation blocks. Building is 1970s. Some of ventilation blocks/bricks have been replaced with modern equivalent. The outside walls get saturated with rain. There’s no cavity insulation. I assume the moisture in the cavity drains down to my flat and hits the DPC, then drains out & away through ventilation blocks. Question: where would the moisture exit if there were no ventilation blocks?
1970 detached house with cavity wall filled with blown in rock wool and second floor is hollow block with hanging tiles what can be done to improve the insulation?
You should probably clarify that viewers need to first know if their house is a masonry cavity wall or a timber frame with block outer leaf. If they go around sealing weep vents on a timber frame house, they'll be in trouble (unless they know the specification of the breather membrane - but still risky). Sealing cavities to the roof, around openings and at boundaries is required for limiting spread of fire within the cavity.
I have ventilation bricks in my wall (built 1929) which are definitely above floor level and definitely don't go through to the room. I know this because I had damp coming through my internal wall and on inspection I found that looking through the ventilation brick is was block up with sand. I had to remove brick and dig out all of the sand (god knows where it all came from). All that was on the other side was the internal wall where all of the damp was. The damp wall has now dried out.
Back when people could live below 20C the cavities were all open. Tons of airflow, but not much insulation. Less problem with condensation indoors. Before that it was straight 9 inch with no cavity. Or rock with rubbish infill. Cavity wall insulation is still supposed to sit off the outside brickwork for airflow. Same as roof areas are supposed to have airflow. I remember when they stipulated a 2 inch air gap. And we installed soffit or fascia vents to create that flow. And then tile or ridge vents to exhaust that. Keeping the air moving. Now are you supposed to have no flow. Makes no sense. Not good for the house or the occupants.
The 50mm gap regulation still applies - in roofs its for ventilation, in walls no so, its for water / moisture transfer from outside to in! If moisture can migrate to a cavity or roof void it must be ventilated, if it cannot - it doesn't need ventilation. If you prevent migration (say from a room into a roof space) then the room needs ventilation or damp will occur!
I've got air bricks, I always wondered what they were for. They used to let freezing cold air into my kitchen and even froze a nearby water pipe once. Filled every hole with no more gaps and haven't looked back.
This is a timely video. My house has a rear extension built in the late 1960s. There are air bricks on the outside wall at ground level but these don’t go all the way through to the inside of the house, but appear to be there to ventilate the cavity. The internal walls get particularly cold where the air bricks are on the outside wall, and so condensation tends to form inside at those spots. Should these external air bricks be sealed?
Don't forget that they may be there to ventilate under your floor(s) in the house. If they are - don't close them off! You can find out if the holes are large enough to take a small camera.. or just break one out and have a look (but have a replacement to hand!)
I have a very similar situation. 60's built extension with cavity, no insulation at all. I have one air brick about 3ft off the ground but it does vent through into the cabinate under the kitchen sink. The air brick isn't ducted so blows into the cavity as well. All seems a bit mad to me, I'm thinking of bricking it up to stop the wind howing through into an already cold room.
Greetings from Poland. I absolutely agree with you on this subject. The issue in UK is that often the external or internal walls have so called "rising damp" from the ground due to damage horizontal water barrier. The way we address it in Poland is to cut your whole building with saw and insertion that barrier bit by bit every 20cm you cut. You might think this is an highly professional specialist job. No! It is diy job. One person is inside the house and one outside and they push and pull manual saw to cut you building at low level. Alternatively you can use chainsaw with special chain for concrete. I modern day an age cavity insulation is insufficient. We nowadays do 30cm of external wall insulation when upgrading existing builds. On the top of insulation goes mesh net, cement based glue, and 3mm render to finish. I am diy-er not professional.
Off topic, but a return to tackling mould with PIVs might be interesting. Now that they’ve been around a while, a short-ish review of the tech would be good. I’m seeing some pieces saying they’re effective, but they drop room temperatures, even with the heated air versions.
@jimw6659 They are just an extractor fan in reverse. They can work well, especially on still days, when the normal wind gusts are not pushing air in though passive vents & then allowing it to flow out again when the gust stops. Everyone goes on about extract fans, but you have to think about the whole airflow. Extracting is fine, but new air has to come in somewhere. If an extract in the bathroom, for examples, is just sucking air from form a trickle vent in a window next to it, then it is doing nothing, just short-cycling. The air has to flow across the room to get the moisture out.
What about the weep holes at the outer leaf of the brick cavity wall midsection & bottom of the wall? Aren't these supposed to drain the water inside the cavity away?
Why should it change with 1930's? I have a house that is 1905 and it is cavity filled with zero damp and cavites are closed with no ventilation. Please explain why you think that it should be different.
You should also address the problem of the inner leaf continuing higher than the outer, to support roof trusses. The outer is lower because of the slope of the roof. The room's ceiling is therefore higher than the outer leaf, ie the level of the soffits. The insulation needs to continue to the top of the inner leaf otherwise you have a cold band below the ceiling which is in effect a single leaf . We had Shell insulation, glued together polystyrene beads but it can't go higher than the cavity. No-one seems to accept that the insulation needs to be continuous.
An Insulated cavity should not be closed off at the top, this allows the continuety of the wall insulation to join up with loft inulation with no break between. Close the top and cold bridging occurs.
Our problem regarding air bricks takes on a different approach, where our 1963 3 bedroom bungalow was constructed using a fabricated steel frame which includes the roof. A brick wall makes the outer shell, and a 45mm plasterboard inner wall completes the structure. Bichemin was used between the bricks and steel and plaster and steel to keep contact away from the damp walls. We cannot insulate our inner cavity as the steel needs to breath and remain dry. So our choice to bring this 1963 building up to scratch is to add 100mm of outer insulation to the walls all the way round the bungalow. The air bricks are a concern, because wind can create a draft under the floor space and up through the cavity. But if the walls are to be sealed by a water proof rendered insulated layer, water penetration should not be a risk. So does this mean I can close off the air bricks? Currently the system has work for the last 88 years and kept the steel rust free. We have an ASHP to provide us heat for the home, but it does struggle once the temperature out side reaches -5c. We need to insulate!
We have a 20 year old "new build" in a modern housing estate, this cold recent snap we have noticed a but of condensation on the inner black roof membrane and the tops of the timbers are a little damp. Should we be worried, or will it all sort itself out once the weather warms up please?
If you have caity ties and the cavity gets wet for whatever reason,the insulation would get wet ,cavities where there to keep the internal wall from getting wet,thats why they put air bricks in to circulate air
I think that's the case with my house. Airbricks below dpc level, house was built with coal fires. Coal fires no longer, but a howling wind under the house sucking out all the heat. Often wondered if it would be feasible to seal them. Have timber suspended floors which I don't plan changing, I assume part of the original design was to prevent these rotting. I often wonder if a heat pump/heat recovery system could be fitted under there to act like a sort of underfloor heating, but never heard of anything like that being available.
I live in an early 1960s bungalow, one of many on this area to the same design. They are all prone to mould in the same corner of the bedroom, where there are two outside walls. It's probably because the occupants exhale moisture all night when it's coolest, which condenses in that corner. My neighbour has a vent in that corner, inserted since her bungalow was built. It is only in the external wall; it does not go through to the bedroom. I think it was inserted to try and cure the mould problem. It doesn't. She insists on having the vent left clear (it's on the boundary of my garden) so I leave it clear. Would she be better off blocking it up?
Hi Roger, really interesting that you say the cavity SHOULD be closed at the top, as the house I grew up in was ex-council (built 1961-2) and also had an open cavity into the loft. In effect, I would guess this means that instead of a 9" wall, you have a sheltered 4 1/2" wall with convection currents up into the loft, which quite possibly insulates less. Unfortunately, it seems so hard to find out what the old rules were (as opposed to finding out what today's rules are, which is somewhat easier), so when you come across this kind of stuff in older housing, it is hard to tell if that was the way they did things then, or if someone was cutting corners back then. If you had a house with this problem, what would you do be inclined to do about it, out of interest?
My house was like it but I closed it all off at the top with rockwool in polythene sacks. That was 30 years ago and it is fine. The airspace is an important insulator. Like you say, a ventilated cavity means you have a 4inch brick wall.
Your videos are always interesting Roger! I have air bricks that are below floor level, but have a concrete floor (late 1970s bungalow). Does this mean the floor is in fact block and beam, and there is are space underneath it? Cheers
Dutch here. In about 1978, our neighbors took out the wooden floor and poured concrete on sand. Then we got rising humidity in our living room. In 1980 my father took out (with an other side neighbor) our wooden floor, 4 by 9m, and drilled holes to put chemicals in them. Then he installed concrete beams and concrete "breads" between them and filled it on top so that it is flat. Then he installed yellow airing bricks that ventilate the crawl space under the floor. Two on the front sidewalk side and on the back yard side. Problem solved since 1980. Also in this vid you see the area between the bricks and the window being sealed with silicone but that area must stay open. My parents house is from 1905 and the window frame is from 1905 and it is still okay. The bricks do not touch the window frame. I also saw it in a building school vid that even nowadays the young people learn to keep that open for ventilation. In the vid the teacher says that rain will not come in but the normal moister must be able to escape.
someone put a concrete floor in my kitchen which blocks the airflow which used to go under floors from front of house to back. i hope they put in air pipes but i doubt it
Well Roger, as a long time fan of 'Bisby News' :-) i would have to query your assertion that air (whether moisture laden or not) from the cavity could lead to an appreciable amount of condensation in the roof space .. I have no evidence to the contrary as such, but roof spaces generally have a reasonable air-flow for lots of reasons .. so if one were to see a lot of condensation in the roof space my first thought would be to check the roof space ventilation (as we know that some folk stuff so much rockwool right into the eaves that natural ventilation is diminished) .. but carry on Sir, as you put out some great info and there's often a talking point to get our teeth into :-)
Is there a good way to tell if a cavity is insulated without drilling into the wall? I live in a block of flats built in 1995 at whoch point some insulation should have been put in, but I'm getting a bit sceptical.
A cheap thermal imaging camera will show you where the cold spots are. It should have some insulation in there but if the location is exposed it will still be a cold wall.
@SkillBuilder Thank you for the quick reply! I'm actually playing around with a thermal camera atm, but the building looks fairly uniform from the outside - not sure if that means there isn't any insulation or if it's been done well. Will need to investigate a bit more.
No, because air-bricks are there for a reason. I have lived in rental houses where the air-bricks had been blocked-up, and all of those houses had damp and mould issues. When I was a lad, I was brought-up in houses which had open fires. We never had any issues with condensation or mildew because there was always a free-flow of air going through the house.
Generally good advice but not for houses close to the coast in exposed locations. Salt laden winds will always find weaknesses in walls and water will inevitably penetrate into the cavity . For houses close to the coast and exposed to winds the only safe insulation is internal wall insulation. Cavity wall and external wall insulation should be avoided. But if you are not living close to the coast in an exposed location cavity wall insulation is an excellent and cheap option which does make a big difference - the only problem is the installers are, far too often, cowboys
Regulations for brick or block clad timber framed buildings require cavity ventilation top and bottom. That said, I do wonder if what they require is sufficient to make much difference. There is a huge difference between a rendered block wall and a brick wall. Especially with hard bricks, driven rain can actually spurt into the cavity. With wide insulated cavities I believe there have been practically no issues, and any probably poorly fitted cavity trays. Retired Architect. ps, when I started, before sealing the top of a cavity, the builder would go round with a long 2x1” and knock off any snots on wall ties.
@@markthomasson5077 In Australia our bricklayers hose the cavities out every afternoon, they also leave clean outs at the dpc and those that out every day. I don’t see the English brickies do that.
I have a squirrel (or similar) in my bungalow loft space chewing the alarm cables. I have UPVC soffits and fascias and can’t see any gaps. How do I discover where he got in please?
Great video thank you. Quick question please. My house is a semi-detached with an extension on the side (it was there when i purchased the house) the house has cavity wall insulation all but the extension its not damp but its very cold the insulation companies wont touch it because the cavity is less than 50mm is a closed cell expanding foam any good i have been told that it will make the cavity a solid which yeah it would but will apparently cause damp and more issues it seems that all they want to do is try ans sell me external insulation please any suggestions will be more than welcomed
Thanks for that. I have just read it all and it talks about weep holes if you are using a stepped damp proof course. Provided there is no open cavity at the top the weep holes are not vents. I don't see anything there relating to ventilated cavities unless we are talking about timber frame which is an subject entirely I should have made that clear.
Not sure u want kill airflow though the cavities, as it’s a tried and tested way of preventing moisture build up , which could cause problems with damp and eventually rot ( in timbers ) capping the top at the eaves makes sense but sealing up or removing the air bricks at low level, I’m not so sure,trapped air is a great insulator ( as roger says ) but trapped moisture laden air in the cavity is only gonna lead to problems further down the line I reckon , uve gotta somehow come to a compromise between the two scenarios insulation but without introducing a damp issue and airflow whilst trying to reduce heat loss , it’s tricky , especially in a retro fit scenario ( with no or virtually no access to the cavity .)cavity wall insulation can cause its own problems also and any rockwool type of insulation in the cavity is a complete no no ( if it gets damp it will definitely cause damp , especially at low level as it starts to slump under its own increasing wet weight) and the micro beads stop the airflow at low level . Like I said it’s a problem on older properties, not so for new build if built correctly to the regs ( although we all know that don’t always happen 🫤)
Any advice for a house built in 1866 and only has a thumbnail cavity? The house is painfully cold, even after new roof fitting and double glazing replaced.
My house - 1970's concrete lower floor, its a 1 off house. The odd thing it has no weep vents. being honest I think the house seems quite condensated? Should I have weep vents from the cavity to the outside? :(
I have lived in three rendered houses, two of which were rentals, and had some of the worst mould I have ever seen. Rendering a house or painting the brickwork not only completely destroys its character, but makes it like living inside a huge plastic bag. Houses need to breathe.
Houses do not 'breathe.' What you are experiencing is mould growth that is a result of condensation. A dehumidifier will help. If you can afford it, line the walls internally with insulated plasterboard, too.
@johnriggs4929 If you have a good airflow throughout your house, that is what is known as "allowing your house to breathe", and if you do that, you won't need a dehumidifier.
@@johnriggs4929 It's a trade-off isn't it - a warm damp-free and mould-free house again a hermetically sealed house with little or no air circulation. I was brought-up with open-fires in houses with air-bricks venting into every room, and I never saw black mould inside a house until I lived in a rendered house with blocked-up air-bricks. I know what you are saying about wasted heat, and that can't be helped in any house; but everything is going to cost you something. Isn't human health worth far more than just saving heat and money? It is only a fairly modern concept that we need to seal every nook and cranny in our houses to make them as airtight and heat-efficient as possible to save money. When I was a lad, there was only one kid in the entire school who had asthma; Now it seems to be almost 50% of school-age children use an inhaler, and a lot of medical experts put it down to the type of housing that we live in. I know that is only anecdotal, but I know what type of house I would choose to live in.
@@johnriggs4929 It's a trade-off isn't it - a mould-free house with good ventilation, against a hermetically sealed house with no airflow. Whatever you choose is going to cost you something.
If it is a cavity wall with penetrating damp, venting it won't help. If you have a dead air space less wind will penetrate the masonry because it would have to compress the air.
Hi Rodger, thanks for another informative video, we live in a bungalow with these air bricks west facing front and back east. When we moved in most were covered up, I removed all and we get lots of mould on the west side, should I cover all and the loft gaps? George Staszak Mr Combi 🤩
Trapping movement of air more importantly. I'm not sure but I think cavity convection is a thing? Maybe you can clarify this, if true or not, I am thinking of getting the party walls gap filled. I think convection is the reason why feathers are more insulating in a jacket than just air sacks, but maybe it's radiation. On a further point, in many houses we need a bit of heat loss to dry that skin out, most house brick don't last long if they become damp.
Many years ago we got cavity wall insulation , it was a government thing ( seemingly ) where this was pumped into the cavity ans all air bricks are sealed with this gel … my house is 30 years old now with no problems I’m aware of but I often wondered if this was the right thing to do .. any comments . . ?
In my new place to moved into back in May, there’s been a persistent problem with hotspots on the ceiling for condensation and mould build up, there is even a moist/damp patch of wall by the bedroom window, surveyors from the council say either it’s a “slow leak” (why and where from?!) and/or to do with the cavity wall. In rear of the property (I live in a 70s build bungalow) there are two brick air vents which appear to have been filled with expanding foam by the previous tenant! Do I unblock these or not?? Insulation in the loft apparently is sufficient but around the eaves is going to be further inspected by roofers by removing a couple tiles. The condensation and mould appears in bedroom, bathroom and kitchen, and yes I have the trickle vents open 24/7 and open windows daily, even for an hour or so during winter months.
i use a £15 infrared gun thermometer to dind the cold areas in walls and ceilings - they were in the top 6 inches of the walls, i kingspanned them during roof repairs
Im of the view a cavity should be free of insulation and anything that bridges the cavity unnecessarily and the external brick should be vented to allow air to dry out condensation that runs down the inside of the external bricks probably more so at the lower ground level where its going to ultimately end up. Everyone seems to have a different idea about this. My neighbour filled all his airbricks in then started getting mould issues!!
Interesting. I’ve never known a cavity wall to be blocked off at the top. I’d assumed the reason was, there is no significant air flow, as the bottom of the cavity is airtight, but it still allows any excess moisture to rise to the top and disappear in your vented loft. Your taped PIR board would be pressed tight against the inner blockwork, meaning the insulation properties would be intact. I don’t like the idea of sealing off the cavity.
Una cosa es una fachada ventilada y otra una cámara interior. Si la cámara es interior está claro que debería rellenarse con un material aislante y ser estanca tanto para el aguó como para el aire.
We've got a single storey extension with cavity wall insulation whereas the rest of the house hasn't, the extension in theory should be the warmest part of the house BUT the extension has vented sofit, the cavity isn't closed at the top and the interior walls are dot dabbed so air leakage negates the insulation, if I ever can afford to have my own house built I've got all the spec planned out 😂
I would argue that each building design is different so a 1 size fit's all approach doesn't work. Some houses need the airflow/cavity regardless. Filling it will just cause issues. The building next door might be similar but is ok with cavity filled with insulation. Materials used, quality of the job will all effect the outcome.
Pretty sure my double air bricks (double the height of a brick) vent both the sub floor and the wall cavity - I live in a 1960's bungalow. I've always wondered if the air from the air bricks is cooling the cavity and therefor providing heat loss.
I've got an odd internal cavity vent (white plastic louvered thing) on the internal wall of a cavity wall situation. The gable end is north-facing and gets cold bridging along the bottom sometimes causing condensation (the condensation pattern seems like it follows the mortar detritus etc in the cavity) , and I wondered of this was a 'fake' solution to that, or if it was where they put in some fibreglass insulation (which is in there) and never closed it back up properly. It's very strange.
@@chapman9230 Thanks for the reply. 👍There's no open fire in the whole place. I can only assume it was either to placate the previous resident/s about the condensation or to install some fibreglass cavity insulation, it just seems very odd. It doesn't go through to the outside wall and isn't sleeved, when you pull it off to reveal the hole (5/6 inches across) you can see the insulation so maybe it was to do with installing that, but I haven't yet come to a satisfactory conclusion about it. For example someone suggested it might have been for a tumble dryer exhaust, but as it doesn't go outside and is in a position where you would never put an exhaust/dryer I have ruled that one out.
@@thesunreportI suspect it used to go to outside and be sleeved as a vent for the room. But then when cavity wall insulation was retro fitted they bricked up the outside vent and just left the inside with the vent face.
@@owensmith7530 Thanks for the reply. 👍. There's no sign it ever went outside, the outer wall is inact and uniform, so it would be a literal miracle if somone retrofitted bricks so perfectly, and judging by the other, sometimes very untidy repairs (it's a housing association property) i can't see how the vent ever went outside. The insulation inside the cavity is standard fibreglass loft insulation, and again there doesn't seem to be a way that you could stuff that around the whole cavity, so to be honest I think the internal vent is a bit of a blag. I have raised the gable-end condensation with the housing association, and they have been a bit tricky about it, blaming me for not running bathroom and kitchen fans 24/7. I've spoken to another resident and they don't use their fans like that, and they don't have the gable-end condensation either. The two other properties in the development don't even have a kitchen fan, and they don't get the condensation as far as I know. One of the housing association 'experts' took photos of the bathroom fan switched-off so he could put in the report that it was my fault that the bedroom/lounge got condensation, which I thought was pretty disingenuous, but a trickle flow in a separate room wouldn't do anything for that condensation, and there's no mould in the bathroom etc as I always run the fan until it's dry in there after a shower etc. The 'expert' also said that 'It's not happening at the other properties', as if I was causing a fuss, even though I've bought a dehumidifier to counter it, so I am doing what I should reasonably be doing to combat it. The real problem I think (with a bit of DIY/building experience behind me) is that it is a fundamental issues with how the place was built, which creates/excaerbates the issue. At the gable end, the outside ground level is about 2 feet lower than the inside floor level. Imho you can see from the height-level of the rainwater/guttering drains (about 5 inches above the ground) that the outside ground level is unusually low, which is unique to this property it seems. I think this is letting the cold into the floor slab and into the bottom of the cavity where the mortar detritus builds up during the building process. This is making condensation along the bottom of the bedroom/lounge wall and floor, but not uniformly as a window would do, making me think it is cold-bridgeing through the uneven detritus in the cavity and floor slab. The condensation goes about 10 inches above the floor at it's highest and about 15 inches across the floor. There was no flooring in that room when I moved in, but there were those tack strips for a carpet, and I suspect they removed the carpet because it was damp. You can see that with the previous resident that the condensation was so bad that it actually mixed with the wall paint and ran down over the skirting board, leaving stains on the skirting board. The only real solution to it as far as I can see would be to fit insulated plaster boards along the gable-end wall internally, but judging from the housing associations response,. they will never pay for that. At about £100 a pop the boards are expensive and I think the best outcome I can hope for is to pay for the installation of the boards myself, and hope they would contribute their in-house plasterer to finish it. I can't put any furniture etc against that wall, and I don't want to put in flooring until it's sorted out, in case it rots out again. I think a good quality insulated underlay under laminate flooring should be enough to stop the condensation on the floor and with the insulated wall boards as well that should solve the problem. All I need now is the £1500 or whatever to get it sorted. 🙁
Hi Roger, we have the small ball insulation pumped into our cavity at the front, it was done before we moved in , we’ve had new windows fitted but every year we get black mould growing around the window reveals and above the rsj. Do you think it would work if we sucked out the insulation with a hoover, someone suggested it’s causing a damp bridge? Cheers
@ we’ve got a dehumidifier on the landing with all the upstairs doors open running all day, the inside of the window reveal is damp and above on the rsj but the window glass is dry ?
I've started seeing quite a few Cavity Wall Insulation Removal Vans in my area recently. Why might that be Rog? Not being facetious. After a recent outbreak of dry rot in a suspended timber floor I wouldn't dream of bunging up the cavity wall in my old 1930's semi. Horses for Courses? I'm also up North, tis Grim.
It may be there as ventilation for a fire or open flue boiler. If they are no longer there you can block it up. Better still put a hit and miss vent cover so you can open and close it.
Hmmm. Not sure this applies to the hundreds of thousands of houses built with soft brick & lime mortar. Water permeates through the outer wall into the cavity in wet weather & dries out in warm weather. Without the cavity being ventilated it might take too long to dry out?
That is where I lose you. If lime is porous (brethable) and wind blown rain gets through, what is stopping it evaporating back through the wall? I have a lime mortar built house and the cavity walls are sealed and fillled with blown mineral insulation. They are completely dry.
Hi Roger having worked with cavities and insulation on the Architectural Technical side, for many years, it needs to be pointed out the fact Cavity are now wider and interstitial condensation calculation including a dewpoint calcullation needs to be done , when filling a cavity with insulation. I do not agree with you saying cavity needs to be sealed. With the increase in insualtion a flow of air is required through the cavity from the weep holes above the cavity tray and into the loft space, where the insulation shjhould be elither at cieling level or rafter level. A flow of air is important , thick of a chimmney. We can not live in hermetically sealed boxes, nature needs a air balence flow which is calculated!
As a young mechanical building services draughtsman, many moons ago I used to calculate and draw temperature gradients through walls (of various constructon) to see where/if interstitial condensation would occur. I would then advise the architect on a remedy, if required. This was before computer programmes
Ah so I could trying to block the cavity left open in the loft ? I have them open and get the odd rat every now and again coming it. God knows from where but keeping it in the wall in better than the loft.
I had a call, after cavity wall insulation fitted, mould and damp build up. Now the FB damp & condensation group would be jumping all over this as they see cavity insulation as the devils own work. I actually posted my thoughts & solution as below & got banned! What it was, was the air-vents fitted in most rooms, had not been sealed where they go through the cavity. House built before we had plastic vent liners. So the vent hole also got filled with insulation thus blocked the vent. Simple solution, tap out the old plaster vent and fill around the cavity with squirty foam, to hold the insulation back. Fit a new plastic vent.
No. Timber frame cavities must be ventilated at high and low level at each storey with perpend vents. I’m surprised and disappointed that this wasn’t mentioned as timbers frame is the predominant house construction type nowadays.
You don't dry your clothes after washing by putting them in a closed plastic bag, you let air movement (draft or wind) on them to dry them out. So how does sealing the cavity help get rid of any moisture build up, be it from penetrating water from rain on the ouside courses of brick, or inside from a leak of some kind. Once you get moisture laden air you have condensation somewhere. Lack of air movement in houses is one reason we are seeing so many pictures and click bait stories of black mold. I love seeing these pictures of huge horrible mold in houses - basically means they are too lazy to clean it off !
This is also my logic, better blowing into the loft than soaking into the internal skin? Or mold filling the cavity. Perhaps this is in reference to new builds. Either way, often these short 3m videos leave more questions than answers. Rogers longer form content is much better.
If you have alot of moisture in you cavity there are propably things you can do first to avoid that. But ofcourse you can live in a area or in a house were cavity insulation is just not an option.
Black mould is a PITA. We have all upstairs windows left on vent 24/7. The bathroom and kitchen have extractors venting to outside and I clean the grilles and duct once a year (doesn't need anymore than that it as even then they aren't particularly dirty). I open all windows in the house for 10-15 mins twice a day. There is a 'healthy' draught unser the front door too. The children have a moisture absorber (unibond ring shaped model) in their bedrooms too. Probably only removing trace amounts of moisture each and only a portion of any excess when their blinds are closed which will almost seal off the vented window area. We still get black mould growing in the bathroom on the walls and ceiling and a bit in other rooms around the window reveals. We hit it with a dedicated black mould remover every so often (tried both HG and the Bang brands). It always comes back. Victorian house with no obvious damp issues - we had areas that were picked up when we bought the house treated and that seems to have been good for the ast 19 years - skirtings, plaster, paint no problem at all. Central heating to every room although generally set at 18 unless we're feeling the chill and then we go up to 19.5. Not sure what is going on but it's annoying. Not huge patches of the stuff and we're all relatively young, fit and healthy so not at major risk from it. Be nice to get rid once and for all though.
@@thebrowns5337 Not an expert, but sounds like your double glazing is pretty good, and so water is condensation on cold spots around the house. (Reveals where innerleaf is bridged to the outer leaf and causes a cold spot). Bathrooms are extra humid, if you ever get it refurbished use backboard like Jacko which is insulating. Extractor fans you have might be useless, someone on YT did a video demonstrating the lack of Static pressure from most cheapies, might be worth upgrading them. Worst case, fit a PIV, tons of good testimonies.
@@chrisallen5548but it wont completely will it. In the long winter months with any driven rain and even condensation, that cavity would remain damp and begin to mould up on any smooth surfaces in particular. I would personally leave the top of the cavity open and insulate with something that doesn’t hold moisture. That is unless you can, with absolute certainty, prevent any ingress, apply lateral vapour control and seal the cavity entirely with no airflow. Borderline impossible.
I live in a post war council house since 1987. It wasnt until they filled the cavity with insulation 25 years ago did i start getting black mould patches. Can't say the house feels any warmer with it either. Just more damp & condensation.
It would have been better to have left it alone.Our house when it was build they put like blanket stuff in the cavity.I must admit it never caused any damp at over 40 years.
Cracking insight into a mysterious world for most people, Roger. Crisp, to the point, clear and accurate. What more could we want. Cheers.
Bit of extra history I discovered as a building surveyor: large air bricks were often placed above the DPC level to ventilate larders or pantries in houses built before the widespread use of fridges. You can normally identify these 1. Where they directly align with a large larder or pantry and 2. If it was on the north most facing side of the house out of direct sun light. Roger is right most of these ‘wall airbricks’ are to ventilate a room though.
my Mum had a "pantry" under the stairs before the advent of electric fridges, comprising of a zink screen in front of an air brick and food sat on a marble slab, one tuesday she had a nasty shock and chucked half a joint of beef crawling with maggotts and blueflies, that was dinner, bastards.
I think I might have one of these - no larder (anymore), but it opens up into the kitchen. Would you say these are no longer needed? It's letting in a huge draft.
@@dagmarbelesova4284 Depends on your current kitchen set up really mate. Kitchens do require good ventilation as a lot more moisture than people think is produced from cooking, tumble driers and boiling kettles etc. If you use other means of ventilation such as extractor hoods, a mechanical extractor fan or are just generally good at opening windows and heating your house well then yes you could probably loose the airbricks.
If don’t utilise any of these ventilation methods then there is nothing stopping you from temporarily covering the airbricks and then buying a cheap humidistat off amazon to monitor for high humidity in the kitchen and also performing visual checks for mould/condensation patches before deciding whether to remove them.
Hope that helps!
@Fraser-B Thank you for the quick and comprehensive reply, that's super helpful! I've noticed the windows misting up so I always open them and use the extractor when doing anything in the kitchen. I think thr utility of the vent is limited now anyway as it's hidden behind the kitchen cupboard. I might consider an extra tor fan or a single room MHRV, the vent just doesn't seem like a great solution atm as it can't be closed or controlled in any way.
We purchased a mid eighties house late summer with solid concrete floors, cavity walls and air bricks above the DPC. Some minor damp issues on survey that surveyor advised was probably due to poor ventilation? Come the winter the damp became worse and we had problems with wood lice crawling around ground floor. Next summer we had air bricks removed, guess what come the winter? No damp issues and no wood lice.
When I was an apprentice, regs were just introducing insulation into 50mm cavities! My mentor always moaned about it bridging the cavity and reducing air circulation and the batts making rags on the ties causing damp.
The price per 1000 didn't go up though, I think that was his main gripe!
I was always stunned by the sheer simplicity of cavity wall insulation sales folk. They'd knock on my door and ask if I want it, I'd tell them it's a Victorian house - with solid brick walls. They'd say 'oh'... and then go next door, and enxt door to that etc. In a terrace of houses exactly the same, getting the same answer each time.
They have now moved onto the highly toxic and flamable external insulation. So they're having to be told what a conservation area is by everyone that answers.
I'm in a conservation area and I'm having external wall insulation. It was approved with no conditions by the council. It would only be if the parish council are staunch traditionalists or if the house is listed that you might have any issue.
It would only take one, probably elderly, houseowner, who doesn't know/understand they have single skin walls, to say yes. Then they could turn up, drill a few holes in the walls, make some noise and pack up.
Flammable are you sure
@@peterthebricky
Just looked one up, has Class E fire rating, which means it is combustable and has a high contributes to the fire.
Edit; The class E was a polystyrene based one.
I can see Kingspan have some class C and Rockwool has an A1 - so if you are getting external insulation, go for something that seems fireproof like Rockwool.
😂😂😂😂😂😂😂@@gcunn1
Here in Australia the top of the cavity and the cavity itself are left open to vent the cooler under floor air. This keeps the house cooler in summer and keeps the underfloor drier.
yeah a lot of people forget about pre AC construction in hot environments
You wouldn't be doing that in Shetland mate lol!
Hard to find two climates more different that Britain and Australia.
Hi Roger, At Last...!!! It took me forever to find a video on cavities. It seems everyone talks about window reveals and door reveals, but you are the first I can find to talk about the top of the cavity. Thank you for clearing this up. There is not much information on the top (eaves) of the cavity and how it should be sealed. Also it seems that not many of the eaves I have seen on older houses seem to be sealed in the construction. Maybe an oversight or just lazy builders. Thanks Roger and the Skill Builder team...
My 1911 terrace has lime mortared cavity brick walls. The cavity is ventillated externally by huge cast iron vents a the top and bottom, plus gaps into the cavity above all the sash window frames. After 100+ years the walls are beautifully stright with apparently no issues with corrosion of the wall ties, but I hate to think what could happen if I messed with the cavity ventilation in any way.
If it ain't broke, don't fix it! 😁
I'd suggest it would be worth filling the gaps on the inner skin around the windows as the gaps will allow moist internal air into the cavity. You may be lucky in any case, and have wall ties that don't rust (wrought iron lasts for decades even right by the sea and regularly submerged in saltwater, and I think some early types of tie were even brick-based).
I'm not against changes and improvements myself. My own house has a 9" solid exterrior wall, which isn't its worst feature, but the wall does get cold in the winter and hot in the summer and is pretty awful thermally. I think the problem we have is people rushing into a one-size-fits-all approach, often by inexperienced installers and without consulting people with a thorough understanding of how historic buildings work.
I did insulate my suspended timber ground floor, and found it to be a significant improvement on an uninsulated one, but I can see how this could easily be done wrong and also cause trouble.
Could you present a video series designing/managing/building a house built to your best standards. The idealistically built home. Include everything from purchase to plans to permission, consultations with trades. Link videos to why that x is best practice. How much it would cost a normal joe. Could even get a building merchant to sponsor it.
Cheers.
Okay... I am an Engineer (old school), who is in the later stages of building a timber frame passive house. I have a rendered block outer leaf with 50mm cavity. the timber frame has a semi permeable foil/fabric layer onto 9mm OSB sheathing, which in turn nailed to 235mm inner leaf timber stud work. The top of the cavity wall is closed off with fire socks.
The semi permeable membrane works on an "Osmosis" method where it allows residual moisture content in the frame to escape into the cavity. If that cavity is fully closed and saturated with moisture, like after having heavy driving rain then sun heating the wall, creating high humidity, this effect will be diminished.
Also by having cavity trays at DPC level and above Lintels, there are weep vents at 900mm intervals, so there will be air movement to a degree. The fire socks around the roof line will stop air to the attic space, and also fire if it does happen. I believe that having a closed off cavity will eventually impact on the timber frame in the future. Because of my fears, probably unfounded, I will be painting the render with ProPerla paint when the weather warms up. Apparently, hydrophobic paint is the way to go nowadays.
@adamsweet3587 could you not install a soffit/fascia vent so any moisture goes outside and you maintain the firestop..? I would also paint the render...
How does cavity 'saturate' with moisture after heavy rain? What is the point of building an external wall if this occurs - bricks absorb / pass water through VERY slowly so unless under water or direct heavy rain for weeks and weeks, its not going to happen! If you are building with an internal breathable skin then that MUST be ventilated on its outer face - the design is not correct if not, you are mixing methods and not in a good way!
As long as you're weep vents are 65mm high and you have them at 900 centres above and below any fire socks and at dpc level at the ground, this should be sufficient to properly vent the cavity. Here in Scotland for timber frame construction, the regs require cavity vents of at least 300mm2 every 1200mm. You should get more than that if your vents are at 900 centres.
@@kawazukisoddbits2717 If you have a closed cavity and have a damp inner side of the outer leaf, and after a period of driven rain, the eventual sun will initial warm that wall to create a more humid environment, until the wall outside dries, to then pull back the moisture to the outside. The levels here maybe very small and will not affect the inner leaf and I am probably being overly too critical. Traditionally cavities were open at the top and roof eaves had ventilation either in the soffits or as vent bars sitting on top of the fascia boards(which the tile sat on), so you had a vented loft space. My house is on a hill (in Cornwall), exposed, South facing, and the South West weather fronts do push hard on my facing walls.
@@WilliamBell-tj9sq Yes, I do have weep vents at DPC and Lintel levels, so when my exposed house experiences high winds, which it does, it will force air from the exposed side around to the other side which will be at lower air pressure. I am probably being overly critical of my situation.
Housing designed with vented cavities ( 1920s,30, 40, 50, ) are best left vented. The cavities are open at wall plates for ventilation of roof timbers and timber floors.
This method of construction was practical, to prevent dry rot.
I do not agree. Venting a cavity into the loft increases moisture and leads to condensation.
@SkillBuilder the underside of my slate roof certainly gets very wet, open topped cavity
That's exactly as I was taught, at technical college, in the sixties. It may be correct, it may not - but that was the official, recommended policy.
Filling a cavity with insulation bridges the cavity and allows water to track onto the internal wall and is particularly poor building practice.
Have you been living under a rock for the past 30 odd yrs? Fully filled cavities have been used and APPROVED for use in this time! Bad workmanship is the cause of damp penetration!
@ It is like putting a sponge inside the cavity retaining moisture . It bridges the cavity and draws water across the dry interior skin. It also promotes corrosion of the wall ties. Unless the exterior face of the wall is sealed with a properly sealed foil and reasonable gap maintained water will track across. It is such a stupid idea approved by officials that have had a mind fart.
It has never been legal in my country. We frankly still have our brains turned on.
@ It cannot work, you are putting a sponge inside the cavity and tracking moisture to the dry skin. You are also jeopardising the structural integrity of the building by creating a moisture soak at every wall tie encouraging them to corrode. It could work with foil faced insulation but a cavity should still be maintained. Whoever approved that 30 years ago was having a brain fart.
It’s not legal where I come from we still have our brains turned on. Seriously it is absolutely nuts, and fixing it with a paint on sealant is bs too. It’s poor building practice.
@davidconnolly7346 not arguing but where are you from. I'm in essex UK, I've laid bricks since 1986 with full fill insulation in 95% of the cavity work. I've yet to have a comeback. Modern full fill bats are water repellent but the older stuff not so much
The primary role of the cavity is to waterproof the building not provide a location for insulation. A way better method if you want additional insulation is brick veneer with the insulation within the interior timber wall. We leave our cavities open in Australia. We get so 3:04 much rainfall too. Cavities get a lot of water inside them, they also need ventilation to dry them out. It’s been working for 100’s of years.
What do you do in England when all the wall ties corrode due to all the moisture trapped inside the cavity, condemn the building?
In a brick/block built building with a cavity that is fully sealed, how does moisture from driving rain seeping into the cavity escape?
If the cavity warms up and has moisture, shouldn't there be somewhere for the moisture to go?
Could a fully sealed cavity with no air flow cause dry rot?
Does 'Rockwool' style cavity insulation allow air flow when the cavity is fully filled with it? Does it soak up and hold moisture or does it transfer it to the internal skin?
These are the discussions I have on site consistently over the years and everyone has a different view.
Personally, as a Bricklayer, I never seal the cavity at the top, I don't insert air bricks to the cavity and I prefer to use Rockwool type insulation when I can. I've never experienced any issues but I still don't know if that's the right way to go or not after more than 40 years on the trowel.
If rain is seeping into the cavity, the cavity is not fully sealed. A fully sealed cavity does not even let air in, much less water. If water can seep in, it can also evaporate through the same opening. Or weep holes at the bottom of the cavity. Now a fully sealed cavity might get a bit of water soaking *through* the external brick. But that's going to be very little, only in huge driving rain storms. And will evaporate quickly when the rain stops because there's very little of it. The water vapor will slowly move through and out of the brick. I've never seen it cause rot.
Rockwool's main function it to prevent moving air. It's hydrophobic but even hydrophobic structures can be soaked with enough water. It will quickly drain, but it absolutely can be soaked. Hydrophobic just means it won't wick water into itself. So a few drops will sit on its surface. But running water will soak it.
Sounds like what you're doing is having an open cavity filled with rockwool. So the rockwool prevents drafts, moving air. Can get soaked, but because it's open it will also dry out quickly.
Perfect example why rockwool became popular. It's easier to stuff an accidentally or intentionally open cavity with it. Than to make sure the cavity traps air.
what happens in central Europe with driving rain? We do not have any cavity. Majority of houses are built from thick clay blocks of 440 mm thickness with many compartments in them holding the air / insulator/ or polystyrene beads or rockwool for isolation. No problem with dampness or thermal bridging and rain is no problem also,
Central Europe's climate can compare to Britain's rain and humidity around the year. Some years they don't have a summer.
It seems that some people confuse ventilation, draining and breathability. In the east of England where i now live most buildings up to 1960 are built with solid walls because it's a dry 2:49 climate and the bricks were low poroucitty with lime mortar; hence no need for cavities. There's no point allowing wet cold air to circulate against the internal skin which is transmitting moisture from the inside thus causing condensation which shows as damp on the bottom of the inside wall.
Very interesting.. I think that’s my problem.. thanks for the insight..👍
I have a 1928 built detached house with a cavity. The parlour was built with a suspended floor. There are air bricks front and rear, wind blows right through. However, the cavity has openings below floor level so wind blows up the unfilled cavity. There are air bricks level with the top of the 1st floor windows, these are unsleeved with cast iron sliding vents. The cavity is open at loft level. Effectively I have a single skin house as the walls are cooled (but dry) by cold wind blowing through. The walls inside are really cold. I have a lot to sort out!
You place sounds similar to mine, built around 1930 for heating with coal fires that no longer exist, but with a howling wind blowing underneath sucking out all the heat! The cavities were filled with insulation in the past but it leaks out everywhere. Some way to stop the wind blasting under but still allow circulation and removal of moist air is something I'd love to find. I've often imagined a heat pump or heat recovery system being fitted under there to provide a kind of underfloor heating, unfortunately never heard of such a thing being available! 🤷♀️
Here in the uk we like to block all vents with new drive ways and wonder why we get damp LOL
I'm in the process of liberating my airbricks. The house started with 5 in 1880. Two buried under paving. Two rendered over. And one had an extension built over it.
I just don't understand why people look at things like that and assume they were put there without good reason.
Last 2 months i build an extension on my house. I filled our cavity with insulation about 3 years ago, so i was a bit nervous how it looked on the inside after removing some walls (in cold and rainy weather). You dont know how it goes in the cavity, maybe it is a bit wet or dampy or moldy. But it was a perfectly fine, dry insulation, dry bricks, no heaps of insulation flocking together etc.
I have to say we do ventilate alot in house and the house is build in 1970, so the bricks and joints are good.
I do think if you have a house with bricks and joint that are more porous or broken, you better re do the joins and impregnate the bricks before adding insulation.
With a cavity you get heat transfer from radiation + convection. Ideally you want to stop the air moving in the cavity without incurring additional heat loss via conduction.
At 0:48 why is that airbrick slightly below ground level? Rain water is going to run into that airbrick, an airbrick designed to remove damp is letting it pour in.
Because the owners have allowed the outside ground level to be raised above the damp proof course which will be immediately below the base of the air brick. The ground level, whether solid as shown in this case or just dirt, should be maintained as required by building regulations to be a minimum of two brick courses below dpc level. Ignorance is what has brought this about and a recipe for a future disaster.
the most trusted and the best.... very grateful. my benchmark for the work I do. thank you.
Up untill the early 70s with the advent of cavity insulation all cavities were sealed at roof level and all air bricks wether pantry or floor insulation were chanelled through the cavity with propriety clay sleaves or slate, since cavity insulation appeared cavity insulation has to meet the roof insulation to avoid cold bridging so sealing cavities is a thing of the past.
My parents house built in 1960 has ventilated cavities and under floor space, and has no weep drains or cavity sills so the cavities have to be ventilated otherwise the footings will get wet with the moisture running down. It is a detached property, and when the outside temperature drops below zero C the heating has to be run 24 hours a day to stop the house getting cold. It can't have cavity wall insulation installed, there is too much very random stone in the front and back walls and also due to the issues with no cavity sills at the bottom.
My house built in 1987 has cavity wall insulation and no air bricks. The cavities are open in the loft, but they do not connect to the loft insulation there is at least 150mm all around the edge with no insulation. This is clearly not an accident, they don't connect anywhere. Also the roof line is low so the outer skin of the walls is about two bricks short of reaching ceiling level, so it would be extremely difficult to connect the two sets of insulation. If you did the soffit vents for the loft space would be blocked, hence why it is clear this is part of the design and not a mistake.
Our 1930s house has a cavity that is unsealed at roof level.
They want a house like an envelope of insulation and air thight so the only air coming in is through the air vents not leaking everywhere ... I use the extraterm full cavity fill with the plastic front and it leaves 10mm air gap on the eternal block... and keep the internal leaf thight against it.. I don't like to see people pumping these cavitys especially brick cavitys as they are so porous
Because the driveway has been raised (Block paving) remove airbrick replace with a brick and install a new airbrick above
Question
I live in a 7-storey block of flats, ground floor. Traditional brick construction. Humid coastal Dorset. Outside walls have ventilation blocks. Building is 1970s. Some of ventilation blocks/bricks have been replaced with modern equivalent. The outside walls get saturated with rain. There’s no cavity insulation. I assume the moisture in the cavity drains down to my flat and hits the DPC, then drains out & away through ventilation blocks.
Question: where would the moisture exit if there were no ventilation blocks?
Very good explanation. Air (besides vacuum) is the best insulator. Just requires the attention to make sure it is trapped air. And it's also free.
1970 detached house with cavity wall filled with blown in rock wool and second floor is hollow block with hanging tiles what can be done to improve the insulation?
You should probably clarify that viewers need to first know if their house is a masonry cavity wall or a timber frame with block outer leaf. If they go around sealing weep vents on a timber frame house, they'll be in trouble (unless they know the specification of the breather membrane - but still risky).
Sealing cavities to the roof, around openings and at boundaries is required for limiting spread of fire within the cavity.
I have ventilation bricks in my wall (built 1929) which are definitely above floor level and definitely don't go through to the room. I know this because I had damp coming through my internal wall and on inspection I found that looking through the ventilation brick is was block up with sand. I had to remove brick and dig out all of the sand (god knows where it all came from). All that was on the other side was the internal wall where all of the damp was. The damp wall has now dried out.
Back when people could live below 20C the cavities were all open. Tons of airflow, but not much insulation. Less problem with condensation indoors. Before that it was straight 9 inch with no cavity. Or rock with rubbish infill. Cavity wall insulation is still supposed to sit off the outside brickwork for airflow. Same as roof areas are supposed to have airflow. I remember when they stipulated a 2 inch air gap. And we installed soffit or fascia vents to create that flow. And then tile or ridge vents to exhaust that. Keeping the air moving. Now are you supposed to have no flow. Makes no sense. Not good for the house or the occupants.
The 50mm gap regulation still applies - in roofs its for ventilation, in walls no so, its for water / moisture transfer from outside to in! If moisture can migrate to a cavity or roof void it must be ventilated, if it cannot - it doesn't need ventilation. If you prevent migration (say from a room into a roof space) then the room needs ventilation or damp will occur!
I've got air bricks, I always wondered what they were for. They used to let freezing cold air into my kitchen and even froze a nearby water pipe once. Filled every hole with no more gaps and haven't looked back.
This is a timely video. My house has a rear extension built in the late 1960s. There are air bricks on the outside wall at ground level but these don’t go all the way through to the inside of the house, but appear to be there to ventilate the cavity. The internal walls get particularly cold where the air bricks are on the outside wall, and so condensation tends to form inside at those spots. Should these external air bricks be sealed?
Don't forget that they may be there to ventilate under your floor(s) in the house. If they are - don't close them off! You can find out if the holes are large enough to take a small camera.. or just break one out and have a look (but have a replacement to hand!)
I have a very similar situation. 60's built extension with cavity, no insulation at all. I have one air brick about 3ft off the ground but it does vent through into the cabinate under the kitchen sink. The air brick isn't ducted so blows into the cavity as well. All seems a bit mad to me, I'm thinking of bricking it up to stop the wind howing through into an already cold room.
If you have wooden floors down stairs the vent are for air flow under the floor
We seal tops now with firesocks and cavity closures.
Greetings from Poland. I absolutely agree with you on this subject.
The issue in UK is that often the external or internal walls have so called "rising damp" from the ground due to damage horizontal water barrier. The way we address it in Poland is to cut your whole building with saw and insertion that barrier bit by bit every 20cm you cut. You might think this is an highly professional specialist job. No! It is diy job. One person is inside the house and one outside and they push and pull manual saw to cut you building at low level. Alternatively you can use chainsaw with special chain for concrete.
I modern day an age cavity insulation is insufficient. We nowadays do 30cm of external wall insulation when upgrading existing builds. On the top of insulation goes mesh net, cement based glue, and 3mm render to finish. I am diy-er not professional.
if the rain/damp is driven into an empty cavity how does it evaporate away if all sealed in?
The same way it got in
In modern buildings, that is where wall weep vents will come in
It condenses on the inner face of the external leaf and gravity brings the water droplets to the weep tray and out the front
Off topic, but a return to tackling mould with PIVs might be interesting. Now that they’ve been around a while, a short-ish review of the tech would be good. I’m seeing some pieces saying they’re effective, but they drop room temperatures, even with the heated air versions.
@jimw6659 They are just an extractor fan in reverse. They can work well, especially on still days, when the normal wind gusts are not pushing air in though passive vents & then allowing it to flow out again when the gust stops.
Everyone goes on about extract fans, but you have to think about the whole airflow. Extracting is fine, but new air has to come in somewhere.
If an extract in the bathroom, for examples, is just sucking air from form a trickle vent in a window next to it, then it is doing nothing, just short-cycling. The air has to flow across the room to get the moisture out.
Given the cost of heating the incoming air, an MVHR which recovers the heat would be better.
What about the weep holes at the outer leaf of the brick cavity wall midsection & bottom of the wall? Aren't these supposed to drain the water inside the cavity away?
In the old houses from like 1930s you need cavity ventilation if you fill the cavity or block the ventilation you'll have major damp issues
Why should it change with 1930's? I have a house that is 1905 and it is cavity filled with zero damp and cavites are closed with no ventilation. Please explain why you think that it should be different.
You should also address the problem of the inner leaf continuing higher than the outer, to support roof trusses. The outer is lower because of the slope of the roof. The room's ceiling is therefore higher than the outer leaf, ie the level of the soffits. The insulation needs to continue to the top of the inner leaf otherwise you have a cold band below the ceiling which is in effect a single leaf . We had Shell insulation, glued together polystyrene beads but it can't go higher than the cavity. No-one seems to accept that the insulation needs to be continuous.
The blocks often go up between the rafters and the insulation is laid on top with a ventilation gap
Full fill on a new build wall is ok when it's also being cladded. But if it's not I'll be sticking with minimum 50mm air gap
Thanks Roger, very straight forward and informative ! Great balance and varied comments below too of course 1
An Insulated cavity should not be
closed off at the top, this allows the continuety of the wall insulation to join up with loft inulation with no break between.
Close the top and cold bridging occurs.
Not if you close it with an insulator
Our problem regarding air bricks takes on a different approach, where our 1963 3 bedroom bungalow was constructed using a fabricated steel frame which includes the roof. A brick wall makes the outer shell, and a 45mm plasterboard inner wall completes the structure. Bichemin was used between the bricks and steel and plaster and steel to keep contact away from the damp walls. We cannot insulate our inner cavity as the steel needs to breath and remain dry. So our choice to bring this 1963 building up to scratch is to add 100mm of outer insulation to the walls all the way round the bungalow. The air bricks are a concern, because wind can create a draft under the floor space and up through the cavity. But if the walls are to be sealed by a water proof rendered insulated layer, water penetration should not be a risk. So does this mean I can close off the air bricks? Currently the system has work for the last 88 years and kept the steel rust free. We have an ASHP to provide us heat for the home, but it does struggle once the temperature out side reaches -5c. We need to insulate!
We have a 20 year old "new build" in a modern housing estate, this cold recent snap we have noticed a but of condensation on the inner black roof membrane and the tops of the timbers are a little damp.
Should we be worried, or will it all sort itself out once the weather warms up please?
Taught as an apprentice to close off the cavity.
If you have caity ties and the cavity gets wet for whatever reason,the insulation would get wet ,cavities where there to keep the internal wall from getting wet,thats why they put air bricks in to circulate air
This is very helpful, thank you so much. 🙂
a lot of vents were put in to provide air flow for a fireplace, long gone !!
I think that's the case with my house. Airbricks below dpc level, house was built with coal fires. Coal fires no longer, but a howling wind under the house sucking out all the heat. Often wondered if it would be feasible to seal them. Have timber suspended floors which I don't plan changing, I assume part of the original design was to prevent these rotting. I often wonder if a heat pump/heat recovery system could be fitted under there to act like a sort of underfloor heating, but never heard of anything like that being available.
Hi Roger, so if I seal up in the loft my cavity wall, what would I do about the air bricks on the outside? Would I just leave them so I can get in?
Great work, Roger
I live in an early 1960s bungalow, one of many on this area to the same design. They are all prone to mould in the same corner of the bedroom, where there are two outside walls. It's probably because the occupants exhale moisture all night when it's coolest, which condenses in that corner.
My neighbour has a vent in that corner, inserted since her bungalow was built. It is only in the external wall; it does not go through to the bedroom. I think it was inserted to try and cure the mould problem. It doesn't.
She insists on having the vent left clear (it's on the boundary of my garden) so I leave it clear. Would she be better off blocking it up?
Hi Roger, really interesting that you say the cavity SHOULD be closed at the top, as the house I grew up in was ex-council (built 1961-2) and also had an open cavity into the loft. In effect, I would guess this means that instead of a 9" wall, you have a sheltered 4 1/2" wall with convection currents up into the loft, which quite possibly insulates less.
Unfortunately, it seems so hard to find out what the old rules were (as opposed to finding out what today's rules are, which is somewhat easier), so when you come across this kind of stuff in older housing, it is hard to tell if that was the way they did things then, or if someone was cutting corners back then.
If you had a house with this problem, what would you do be inclined to do about it, out of interest?
My house was like it but I closed it all off at the top with rockwool in polythene sacks. That was 30 years ago and it is fine. The airspace is an important insulator. Like you say, a ventilated cavity means you have a 4inch brick wall.
If a cavity wall doesn’t need airflow, why doe we need airflow underneath floors/joists?
If the cavity wall is timber construction then needs cavity ventilation, same if your floors are timber I guess
Hi Roger If the cavity is sealed , and water penetrates through the outside brick . What happens to that water if it can’t escape . ? Kind regards 🙏
It drains to the footings and soaks into the ground or it hits the stepped damp proof course and comes out through weep holes
Your videos are always interesting Roger! I have air bricks that are below floor level, but have a concrete floor (late 1970s bungalow). Does this mean the floor is in fact block and beam, and there is are space underneath it? Cheers
You can have both, one room in concrete, the other not. Why, i have no idea.
Or it was built with suspended timber floors but filled in and concreted at a later date
Dutch here. In about 1978, our neighbors took out the wooden floor and poured concrete on sand. Then we got rising humidity in our living room. In 1980 my father took out (with an other side neighbor) our wooden floor, 4 by 9m, and drilled holes to put chemicals in them. Then he installed concrete beams and concrete "breads" between them and filled it on top so that it is flat. Then he installed yellow airing bricks that ventilate the crawl space under the floor. Two on the front sidewalk side and on the back yard side. Problem solved since 1980. Also in this vid you see the area between the bricks and the window being sealed with silicone but that area must stay open. My parents house is from 1905 and the window frame is from 1905 and it is still okay. The bricks do not touch the window frame. I also saw it in a building school vid that even nowadays the young people learn to keep that open for ventilation. In the vid the teacher says that rain will not come in but the normal moister must be able to escape.
someone put a concrete floor in my kitchen which blocks the airflow which used to go under floors from front of house to back. i hope they put in air pipes but i doubt it
Well Roger, as a long time fan of 'Bisby News' :-) i would have to query your assertion that air (whether moisture laden or not) from the cavity could lead to an appreciable amount of condensation in the roof space .. I have no evidence to the contrary as such, but roof spaces generally have a reasonable air-flow for lots of reasons .. so if one were to see a lot of condensation in the roof space my first thought would be to check the roof space ventilation (as we know that some folk stuff so much rockwool right into the eaves that natural ventilation is diminished) ..
but carry on Sir, as you put out some great info and there's often a talking point to get our teeth into :-)
Is there a good way to tell if a cavity is insulated without drilling into the wall? I live in a block of flats built in 1995 at whoch point some insulation should have been put in, but I'm getting a bit sceptical.
A cheap thermal imaging camera will show you where the cold spots are. It should have some insulation in there but if the location is exposed it will still be a cold wall.
@SkillBuilder Thank you for the quick reply! I'm actually playing around with a thermal camera atm, but the building looks fairly uniform from the outside - not sure if that means there isn't any insulation or if it's been done well. Will need to investigate a bit more.
So you should block up air bricks if you have cavity walls?
No, because air-bricks are there for a reason. I have lived in rental houses where the air-bricks had been blocked-up, and all of those houses had damp and mould issues.
When I was a lad, I was brought-up in houses which had open fires. We never had any issues with condensation or mildew because there was always a free-flow of air going through the house.
@ so why is he saying to block them up then?
@@GeorgeAusters He didn't. He said that the cavity should be sealed.
George. Please watch the video again and if it still isn't clear I will answer the question. The air brick goes through the cavity not into it,
@@SkillBuilder My air bricks don’t go through the cavity, they’re literally just a brick with holes in
Generally good advice but not for houses close to the coast in exposed locations. Salt laden winds will always find weaknesses in walls and water will inevitably penetrate into the cavity . For houses close to the coast and exposed to winds the only safe insulation is internal wall insulation. Cavity wall and external wall insulation should be avoided.
But if you are not living close to the coast in an exposed location cavity wall insulation is an excellent and cheap option which does make a big difference - the only problem is the installers are, far too often, cowboys
yes, it depends on the weather where the house is
Regulations for brick or block clad timber framed buildings require cavity ventilation top and bottom. That said, I do wonder if what they require is sufficient to make much difference.
There is a huge difference between a rendered block wall and a brick wall. Especially with hard bricks, driven rain can actually spurt into the cavity.
With wide insulated cavities I believe there have been practically no issues, and any probably poorly fitted cavity trays.
Retired Architect.
ps, when I started, before sealing the top of a cavity, the builder would go round with a long 2x1” and knock off any snots on wall ties.
@@markthomasson5077 In Australia our bricklayers hose the cavities out every afternoon, they also leave clean outs at the dpc and those that out every day. I don’t see the English brickies do that.
I have a squirrel (or similar) in my bungalow loft space chewing the alarm cables. I have UPVC soffits and fascias and can’t see any gaps. How do I discover where he got in please?
My house does not have a liner in when i looked through the air brick vents. It is a cavity wall house, Is this wrong? House is 30 yrs old.
Is it timber framed?
Excellent channel
Good explanation of cavity walls.
I get damp on my inner wall and was wondering whether or not to block up a large airbrick on the outside wall???
Great video thank you.
Quick question please. My house is a semi-detached with an extension on the side (it was there when i purchased the house) the house has cavity wall insulation all but the extension its not damp but its very cold the insulation companies wont touch it because the cavity is less than 50mm is a closed cell expanding foam any good i have been told that it will make the cavity a solid which yeah it would but will apparently cause damp and more issues it seems that all they want to do is try ans sell me external insulation please any suggestions will be more than welcomed
I don't have a liner that goes through the cavity on my living room air brick so the air can go into the cavity. I have cavity insulation.
Roger, I personally agree no vents on cavity but check Part C Sec 5 and BS 5250 for venting cavities. You may be surprised.
Thanks for that. I have just read it all and it talks about weep holes if you are using a stepped damp proof course. Provided there is no open cavity at the top the weep holes are not vents.
I don't see anything there relating to ventilated cavities unless we are talking about timber frame which is an subject entirely I should have made that clear.
Not sure u want kill airflow though the cavities, as it’s a tried and tested way of preventing moisture build up , which could cause problems with damp and eventually rot ( in timbers ) capping the top at the eaves makes sense but sealing up or removing the air bricks at low level, I’m not so sure,trapped air is a great insulator ( as roger says ) but trapped moisture laden air in the cavity is only gonna lead to problems further down the line I reckon , uve gotta somehow come to a compromise between the two scenarios insulation but without introducing a damp issue and airflow whilst trying to reduce heat loss , it’s tricky , especially in a retro fit scenario ( with no or virtually no access to the cavity .)cavity wall insulation can cause its own problems also and any rockwool type of insulation in the cavity is a complete no no ( if it gets damp it will definitely cause damp , especially at low level as it starts to slump under its own increasing wet weight) and the micro beads stop the airflow at low level . Like I said it’s a problem on older properties, not so for new build if built correctly to the regs ( although we all know that don’t always happen 🫤)
Any advice for a house built in 1866 and only has a thumbnail cavity? The house is painfully cold, even after new roof fitting and double glazing replaced.
Log burner
Internal wall insulation if you have no damp problems, perhaps
My house - 1970's concrete lower floor, its a 1 off house. The odd thing it has no weep vents. being honest I think the house seems quite condensated? Should I have weep vents from the cavity to the outside? :(
I have lived in three rendered houses, two of which were rentals, and had some of the worst mould I have ever seen.
Rendering a house or painting the brickwork not only completely destroys its character, but makes it like living inside a huge plastic bag.
Houses need to breathe.
Houses do not 'breathe.' What you are experiencing is mould growth that is a result of condensation. A dehumidifier will help. If you can afford it, line the walls internally with insulated plasterboard, too.
@johnriggs4929 If you have a good airflow throughout your house, that is what is known as "allowing your house to breathe", and if you do that, you won't need a dehumidifier.
@Teapot-Dave True. You'll also spend a fortune in wasted heat.
@@johnriggs4929 It's a trade-off isn't it - a warm damp-free and mould-free house again a hermetically sealed house with little or no air circulation.
I was brought-up with open-fires in houses with air-bricks venting into every room, and I never saw black mould inside a house until I lived in a rendered house with blocked-up air-bricks.
I know what you are saying about wasted heat, and that can't be helped in any house; but everything is going to cost you something. Isn't human health worth far more than just saving heat and money?
It is only a fairly modern concept that we need to seal every nook and cranny in our houses to make them as airtight and heat-efficient as possible to save money.
When I was a lad, there was only one kid in the entire school who had asthma; Now it seems to be almost 50% of school-age children use an inhaler, and a lot of medical experts put it down to the type of housing that we live in. I know that is only anecdotal, but I know what type of house I would choose to live in.
@@johnriggs4929 It's a trade-off isn't it - a mould-free house with good ventilation, against a hermetically sealed house with no airflow. Whatever you choose is going to cost you something.
it depends on the weather where the house is, is there a wet wind blowing onto the wall?
If it is a cavity wall with penetrating damp, venting it won't help. If you have a dead air space less wind will penetrate the masonry because it would have to compress the air.
Yes if it's in the UK.
Hi Rodger, thanks for another informative video, we live in a bungalow with these air bricks west facing front and back east. When we moved in most were covered up, I removed all and we get lots of mould on the west side, should I cover all and the loft gaps? George Staszak Mr Combi 🤩
Trapping movement of air more importantly. I'm not sure but I think cavity convection is a thing? Maybe you can clarify this, if true or not, I am thinking of getting the party walls gap filled. I think convection is the reason why feathers are more insulating in a jacket than just air sacks, but maybe it's radiation.
On a further point, in many houses we need a bit of heat loss to dry that skin out, most house brick don't last long if they become damp.
Many years ago we got cavity wall insulation , it was a government thing ( seemingly ) where this was pumped into the cavity ans all air bricks are sealed with this gel … my house is 30 years old now with no problems I’m aware of but I often wondered if this was the right thing to do .. any comments . . ?
In my new place to moved into back in May, there’s been a persistent problem with hotspots on the ceiling for condensation and mould build up, there is even a moist/damp patch of wall by the bedroom window, surveyors from the council say either it’s a “slow leak” (why and where from?!) and/or to do with the cavity wall. In rear of the property (I live in a 70s build bungalow) there are two brick air vents which appear to have been filled with expanding foam by the previous tenant! Do I unblock these or not?? Insulation in the loft apparently is sufficient but around the eaves is going to be further inspected by roofers by removing a couple tiles. The condensation and mould appears in bedroom, bathroom and kitchen, and yes I have the trickle vents open 24/7 and open windows daily, even for an hour or so during winter months.
i use a £15 infrared gun thermometer to dind the cold areas in walls and ceilings - they were in the top 6 inches of the walls, i kingspanned them during roof repairs
I have polystyrene in my 25 yr old house. Put in the cavity by the builders when being built. Was this ok.🤔
if fire spreads to the cavity its too late ! hopefully the alarms have already gone off and youve escaped
Im of the view a cavity should be free of insulation and anything that bridges the cavity unnecessarily and the external brick should be vented to allow air to dry out condensation that runs down the inside of the external bricks probably more so at the lower ground level where its going to ultimately end up. Everyone seems to have a different idea about this. My neighbour filled all his airbricks in then started getting mould issues!!
Interesting. I’ve never known a cavity wall to be blocked off at the top. I’d assumed the reason was, there is no significant air flow, as the bottom of the cavity is airtight, but it still allows any excess moisture to rise to the top and disappear in your vented loft. Your taped PIR board would be pressed tight against the inner blockwork, meaning the insulation properties would be intact. I don’t like the idea of sealing off the cavity.
If you don't like it don't do it but it is the recommended method. Even from a fire point of view it is better closed
@ From a fire perspective, it would absolutely make sense, as you’d remove the chimney effect. Good point.
Una cosa es una fachada ventilada y otra una cámara interior. Si la cámara es interior está claro que debería rellenarse con un material aislante y ser estanca tanto para el aguó como para el aire.
We've got a single storey extension with cavity wall insulation whereas the rest of the house hasn't, the extension in theory should be the warmest part of the house BUT the extension has vented sofit, the cavity isn't closed at the top and the interior walls are dot dabbed so air leakage negates the insulation, if I ever can afford to have my own house built I've got all the spec planned out 😂
I would argue that each building design is different so a 1 size fit's all approach doesn't work. Some houses need the airflow/cavity regardless. Filling it will just cause issues. The building next door might be similar but is ok with cavity filled with insulation.
Materials used, quality of the job will all effect the outcome.
and local weather - in a wet wind or not ?
Almost 30 years ago, I worked doing blown cavity wall insulation. It was the fad back then. Hindsight is always great! lol
Still use it on new houses. At least they were five years ago.
Pretty sure my double air bricks (double the height of a brick) vent both the sub floor and the wall cavity - I live in a 1960's bungalow. I've always wondered if the air from the air bricks is cooling the cavity and therefor providing heat loss.
Have a look, often they have slate to box them so they don't vent the cavity.
@@SkillBuilder Thanks for the reply. If they don't, is it worth retrofitting something to prevent air movement in the cavity?
I've got an odd internal cavity vent (white plastic louvered thing) on the internal wall of a cavity wall situation. The gable end is north-facing and gets cold bridging along the bottom sometimes causing condensation (the condensation pattern seems like it follows the mortar detritus etc in the cavity) , and I wondered of this was a 'fake' solution to that, or if it was where they put in some fibreglass insulation (which is in there) and never closed it back up properly. It's very strange.
Do you have an open fire in that room. If so it may be there to allow air in to feed the fire
@@chapman9230 Thanks for the reply. 👍There's no open fire in the whole place. I can only assume it was either to placate the previous resident/s about the condensation or to install some fibreglass cavity insulation, it just seems very odd.
It doesn't go through to the outside wall and isn't sleeved, when you pull it off to reveal the hole (5/6 inches across) you can see the insulation so maybe it was to do with installing that, but I haven't yet come to a satisfactory conclusion about it.
For example someone suggested it might have been for a tumble dryer exhaust, but as it doesn't go outside and is in a position where you would never put an exhaust/dryer I have ruled that one out.
@@thesunreportI suspect it used to go to outside and be sleeved as a vent for the room. But then when cavity wall insulation was retro fitted they bricked up the outside vent and just left the inside with the vent face.
@@owensmith7530 Thanks for the reply. 👍. There's no sign it ever went outside, the outer wall is inact and uniform, so it would be a literal miracle if somone retrofitted bricks so perfectly, and judging by the other, sometimes very untidy repairs (it's a housing association property) i can't see how the vent ever went outside.
The insulation inside the cavity is standard fibreglass loft insulation, and again there doesn't seem to be a way that you could stuff that around the whole cavity, so to be honest I think the internal vent is a bit of a blag.
I have raised the gable-end condensation with the housing association, and they have been a bit tricky about it, blaming me for not running bathroom and kitchen fans 24/7.
I've spoken to another resident and they don't use their fans like that, and they don't have the gable-end condensation either. The two other properties in the development don't even have a kitchen fan, and they don't get the condensation as far as I know.
One of the housing association 'experts' took photos of the bathroom fan switched-off so he could put in the report that it was my fault that the bedroom/lounge got condensation, which I thought was pretty disingenuous, but a trickle flow in a separate room wouldn't do anything for that condensation, and there's no mould in the bathroom etc as I always run the fan until it's dry in there after a shower etc.
The 'expert' also said that 'It's not happening at the other properties', as if I was causing a fuss, even though I've bought a dehumidifier to counter it, so I am doing what I should reasonably be doing to combat it.
The real problem I think (with a bit of DIY/building experience behind me) is that it is a fundamental issues with how the place was built, which creates/excaerbates the issue.
At the gable end, the outside ground level is about 2 feet lower than the inside floor level. Imho you can see from the height-level of the rainwater/guttering drains (about 5 inches above the ground) that the outside ground level is unusually low, which is unique to this property it seems.
I think this is letting the cold into the floor slab and into the bottom of the cavity where the mortar detritus builds up during the building process. This is making condensation along the bottom of the bedroom/lounge wall and floor, but not uniformly as a window would do, making me think it is cold-bridgeing through the uneven detritus in the cavity and floor slab.
The condensation goes about 10 inches above the floor at it's highest and about 15 inches across the floor. There was no flooring in that room when I moved in, but there were those tack strips for a carpet, and I suspect they removed the carpet because it was damp. You can see that with the previous resident that the condensation was so bad that it actually mixed with the wall paint and ran down over the skirting board, leaving stains on the skirting board.
The only real solution to it as far as I can see would be to fit insulated plaster boards along the gable-end wall internally, but judging from the housing associations response,. they will never pay for that.
At about £100 a pop the boards are expensive and I think the best outcome I can hope for is to pay for the installation of the boards myself, and hope they would contribute their in-house plasterer to finish it.
I can't put any furniture etc against that wall, and I don't want to put in flooring until it's sorted out, in case it rots out again. I think a good quality insulated underlay under laminate flooring should be enough to stop the condensation on the floor and with the insulated wall boards as well that should solve the problem. All I need now is the £1500 or whatever to get it sorted. 🙁
Hi Roger, we have the small ball insulation pumped into our cavity at the front, it was done before we moved in , we’ve had new windows fitted but every year we get black mould growing around the window reveals and above the rsj. Do you think it would work if we sucked out the insulation with a hoover, someone suggested it’s causing a damp bridge? Cheers
You’ve considered it’s more likely the moisture is coming from breathing cooking drying clothes than damp bridge?
@ we’ve got a dehumidifier on the landing with all the upstairs doors open running all day, the inside of the window reveal is damp and above on the rsj but the window glass is dry ?
I have removed the timber floor and made concrete floor can I get rid of the air brick ?
If it's slab on solid then yes, air bricks below DPC are now doing nothing
Yes you don't need the airbricks but it might be easier to leave them if they are sleeved.
@ what’s the best way to cover it as it’s making the house cold with draft
great stuff your the best
I've started seeing quite a few Cavity Wall Insulation Removal Vans in my area recently.
Why might that be Rog? Not being facetious.
After a recent outbreak of dry rot in a suspended timber floor I wouldn't dream of bunging up the cavity wall in my old 1930's semi.
Horses for Courses? I'm also up North, tis Grim.
hi Grim!
Cavities are ventilated by perpend vents. Air bricks are usually for ventilation of voids. Dry rot is different from wet rot.
if theres a prevailing wet wind onto the wall the cavity insulation may get wet
What if I have an air brick above floor level? there's nothing in the room inside.
It may be there as ventilation for a fire or open flue boiler. If they are no longer there you can block it up. Better still put a hit and miss vent cover so you can open and close it.
@@SkillBuilder Thanks, it is outside a bedroom with nothing inside, It's a bungalow and only 25 years old, I'll block it up. I'll block it up.
Ideal conditions for growing mushrooms.
More common sense advice , happy new year chaps 🫡🧱👍🏼
Does the moisture evaporate/drain back out through the cracks between mortar and brick?
Evaporates and drains into the floor, if enough had pooled and there was an escape out the mortar or brick the water would find it.
Hmmm. Not sure this applies to the hundreds of thousands of houses built with soft brick & lime mortar. Water permeates through the outer wall into the cavity in wet weather & dries out in warm weather. Without the cavity being ventilated it might take too long to dry out?
That is where I lose you. If lime is porous (brethable) and wind blown rain gets through, what is stopping it evaporating back through the wall? I have a lime mortar built house and the cavity walls are sealed and fillled with blown mineral insulation. They are completely dry.
Hi Roger having worked with cavities and insulation on the Architectural Technical side, for many years, it needs to be pointed out the fact Cavity are now wider and interstitial condensation calculation including a dewpoint calcullation needs to be done , when filling a cavity with insulation. I do not agree with you saying cavity needs to be sealed. With the increase in insualtion a flow of air is required through the cavity from the weep holes above the cavity tray and into the loft space, where the insulation shjhould be elither at cieling level or rafter level. A flow of air is important , thick of a chimmney. We can not live in hermetically sealed boxes, nature needs a air balence flow which is calculated!
As a young mechanical building services draughtsman, many moons ago I used to calculate and draw temperature gradients through walls (of various constructon) to see where/if interstitial condensation would occur. I would then advise the architect on a remedy, if required. This was before computer programmes
@@MarkJones-ji8fd Can you calculate the amount of water that tracks across the cavity when it’s full of insulation and not being ventilated?
@davidconnolly7346 no, only where in the wall construction condensation was likely to occur
Ah so I could trying to block the cavity left open in the loft ? I have them open and get the odd rat every now and again coming it. God knows from where but keeping it in the wall in better than the loft.
I had a call, after cavity wall insulation fitted, mould and damp build up.
Now the FB damp & condensation group would be jumping all over this as they see cavity insulation as the devils own work.
I actually posted my thoughts & solution as below & got banned!
What it was, was the air-vents fitted in most rooms, had not been sealed where they go through the cavity. House built before we had plastic vent liners. So the vent hole also got filled with insulation thus blocked the vent.
Simple solution, tap out the old plaster vent and fill around the cavity with squirty foam, to hold the insulation back. Fit a new plastic vent.
Does that apply to timber frames
No. Timber frame cavities must be ventilated at high and low level at each storey with perpend vents. I’m surprised and disappointed that this wasn’t mentioned as timbers frame is the predominant house construction type nowadays.
You don't dry your clothes after washing by putting them in a closed plastic bag, you let air movement (draft or wind) on them to dry them out. So how does sealing the cavity help get rid of any moisture build up, be it from penetrating water from rain on the ouside courses of brick, or inside from a leak of some kind. Once you get moisture laden air you have condensation somewhere. Lack of air movement in houses is one reason we are seeing so many pictures and click bait stories of black mold. I love seeing these pictures of huge horrible mold in houses - basically means they are too lazy to clean it off !
This is also my logic, better blowing into the loft than soaking into the internal skin? Or mold filling the cavity. Perhaps this is in reference to new builds. Either way, often these short 3m videos leave more questions than answers. Rogers longer form content is much better.
If you have alot of moisture in you cavity there are propably things you can do first to avoid that. But ofcourse you can live in a area or in a house were cavity insulation is just not an option.
Black mould is a PITA. We have all upstairs windows left on vent 24/7. The bathroom and kitchen have extractors venting to outside and I clean the grilles and duct once a year (doesn't need anymore than that it as even then they aren't particularly dirty). I open all windows in the house for 10-15 mins twice a day. There is a 'healthy' draught unser the front door too.
The children have a moisture absorber (unibond ring shaped model) in their bedrooms too. Probably only removing trace amounts of moisture each and only a portion of any excess when their blinds are closed which will almost seal off the vented window area.
We still get black mould growing in the bathroom on the walls and ceiling and a bit in other rooms around the window reveals. We hit it with a dedicated black mould remover every so often (tried both HG and the Bang brands). It always comes back.
Victorian house with no obvious damp issues - we had areas that were picked up when we bought the house treated and that seems to have been good for the ast 19 years - skirtings, plaster, paint no problem at all.
Central heating to every room although generally set at 18 unless we're feeling the chill and then we go up to 19.5.
Not sure what is going on but it's annoying. Not huge patches of the stuff and we're all relatively young, fit and healthy so not at major risk from it. Be nice to get rid once and for all though.
@@thebrowns5337 Not an expert, but sounds like your double glazing is pretty good, and so water is condensation on cold spots around the house. (Reveals where innerleaf is bridged to the outer leaf and causes a cold spot). Bathrooms are extra humid, if you ever get it refurbished use backboard like Jacko which is insulating. Extractor fans you have might be useless, someone on YT did a video demonstrating the lack of Static pressure from most cheapies, might be worth upgrading them. Worst case, fit a PIV, tons of good testimonies.
@@thebrowns5337 get a decent size dehumidifier
If the cavity is trapped, would that not cause condensation inside and psosibly cause damp and mould?
Yes. 100%
No, Roger said that any water/condensation should be allowed to soak away into the ground.
It would condensate, but then drain away, not much different than venting the cavity.
@@chrisallen5548but it wont completely will it. In the long winter months with any driven rain and even condensation, that cavity would remain damp and begin to mould up on any smooth surfaces in particular. I would personally leave the top of the cavity open and insulate with something that doesn’t hold moisture. That is unless you can, with absolute certainty, prevent any ingress, apply lateral vapour control and seal the cavity entirely with no airflow. Borderline impossible.
Well the inner skin will be warmer than the outer so would not attract condensation - in winter. Airconditioned in summer it might
God I love this channel