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Parapet wall thermal bridging and sweating, new coping stones and ventilation.
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- Опубліковано 22 лют 2020
- In this video, I show a parapet wall that has thermal bridging, and is sweating. Recently we did a lot of other work on this warm roof, that is also a cold roof because of the way it has been constructed. As part of the process of trying to rectify the bad workmanship, we have also changed all the parapet wall coping stones to new coping stones, that have a better drip detail to them than the original coping stones. We also added ventilation to the cavity wall so that any moisture getting into the cavity wall, can escape. The original construction of the cavity wall was not correct and no cavity wall trays were fitted at the flat roof level as per building controls guidance. It was decided that to rebuild the top of the cavity To install a cavity wall tray was a step too far so ventilation was added instead. All of the above specifications To this cavity wall are not correct however without completely rebuilding the walls and making further adjustments to the flat roof the correct specifications could not be abided by. Previous videos on this roof show us fixing ventilation to the cold flat roof area previously this area had sweated and the decking had rotted. Another video on this flat roof shows us fixing an embodiment vent along the main area of the house.
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Steven Dickinson
London Flat Roofing
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This channel is a priceless resource for any roofer, thanks Steve
Wow, thanks
Good work fella.
As a brickie I can agree those cavities were bad. Dropping your coke can in there is just ignorance.
However, remember that installing cavity trays on catnic lintols over openings was not always a requirement with our regulations. So some older work may have been built before they were mandatory. The architects tell me that Cavity trays are there to catch condesation and prevent mold forming on the internal walls but I've seen plenty of cavity tray free jobs and never seen mold.
Personally i think cavity trays are pointless nowadays because brickwork cavities are usually vented top and bottom so condensation is miinmal and any water in there will escape.
I've never seen rockwool cause damp issues as it soaks up condensation and allows for air to circulate through it.
The lack of over hang on the copings was definately a bad thing but I suspect the condesation inside the building was down to the idiots who did not vent the cold deck roof.
Not every problem in this game is caused by us brickies -)
Keep up the good work. Subbed.
well said matey
Good stuff Steve. I wish more builders understood vapour control, insulation, cold bridging, warm roofing & cold roofing.
The London stock is a breathable brick, meaning to be layed with lime mortar. Opc mortor will not let it breathe and any plastic or gypsum on the inside (including flashing)will also lead to problems. I never see any damp issues with soft brick and lime buildings built in a canal or river.
Steve you really know your stuff thanks for sharing.
I appreciate that!
Thank you for sharing. I do find similar cases on daily basis.
Firstly i am shore the copings where the main source of the problem. We only fibre glass Firstly we get the builders to fit cavity closers. Then we bridge that with 9mm osb to within 20mm of outside egde then fibre glass impossible for water to get . The copings have to be wide enough with good deep drip good video
Thanks
So glad i've found your channel, I've currently got a parapet style wall in the middle of two sloping roofs. The Right side is a workshop and the wall that side is continuously (Wet when it rains) and i think this video has completely summed it up for me, there isn't any capping stones its just naked brick with some tiles in the mortar joints. So i'm assuming the sitting water is penetrating the mortar / bricks and running into down the wall.
Perfect timing, I’m quoting a job to install a roof lantern on a flat roof, it currently has 4 mushroom vents with no cross battoning(??) and paving slabs for coping stones. Im suggesting a whole new roof (it’s only 2mx3m)
It's alway a problem when there are skylights as they block the flow of air for venting and sometimes on small roofs to strip it and start again is the way to go. Next week I should publish a video on a way round this that helps
Steve Roofer so my suggestion was gonna be change it to a warm deck roof, she wants a 1x2m skylight so there’s not gonna be much left!
great video love your content however some of the construction lingo goes over my head for example while watching i realised a cavity tray would and should have been important or even essential l but what is a cavity tray and whats its purpose in the build ,thanks for sharing Dave
Nice informative video 👍.
Nooice
Once again brilliant video Steve. When putting coping stones on parapet walls between terraced houses should they have a drip detail?
Yes the drip details should be good and clear of the wall both sides
Hi, great video. My parents had a kitchen extension built in 1988 in NW London. The roof was repaired about 10 years ago (new felt roof installed). They have a parapet wall with coping stones on top of the cavity walls, with lead apron flashing between coping stones and brick work for the 3 layer roof. I notice that a couple of the once weathered sloping coping stones are loose and the mortar fillets have fallen out along with the lead wedges and the lead flashing all as one. I have purchased some Hall clips and wedged the flashing back in and plan to use lead sealant instead of a mortar fillets to fill the gap (if the gap is not too big, otherwise mortar fillets? Is this the best approach?
Also one more question, is it a standard 4:1 mix of building sand to cement to fix the coping stones and should I prime the stones with SBR or similar or just lay on a bed of mortar? (Don't want them coming loose again).
Many thanks.
Hi steve i have a parapet wall to build on an extention its a fullfill cavity drawings parapet insulated to top then coping i was gonna stop fulfill at tray level not window tray level is this wise or should i continue full fill above tray right up to top of parapet ?
First, I don't like fulfil, but that's just the way the world seems to be going. Secondly, yes, you have to insulate the parapet above the tray right to the top
Hi Steve. Do you know if type J DPC supports are essential before putting the coping stones on? Are there other alternatives than the £25 closer/support being sold by the roofing superstore?
Hello there. Your videos are great and very informative. A quick question regarding up-stand height on parapets. I am currently building a flat roof extension with a warm roof. It is bounded on three sides by a parapet wall. I understand that the building regs suggest that the height of up-stands be 150mm although it seems ambiguous from my research. As it is a warm roof construction I am concerned that the stack of materials above the ceiling (195mm joists, furring strips, osb deck, insulation, osb deck) plus the 150mm upstand will will skew the proportions of the parapet. making it overly tall. What is the absolute minimum you would recommend for a parapet height above the finished roof surface?. Many thanks. Rubber4roofs suggested that I should contact you
Well building control is dictating and up staying up 150 mils above the roof level or above the level of any decking on the roof. This can be reduced to 75 mil windowsills however there are other ways of dealing with this depending on specifications and who is actually signing off the work i.e. building control if you would like to contact me I can give you more information please email me on info at London flat roofing.co.uk and we can move this forward speak soon or call 07802300099
Hi Steve, great and very helpful video, thanks for that. I'm looking to do an extension to my house with a parapet roof (I'm project managing but will be employing a brickie), and was hoping you could give some advice. My plan is to do an EPDM rubber roof, and have the rubber membrane running up and over the parapet and over the cavity, with slates bedded on mortar to cover the cavity. My thinking then is that the EPDM rubber will act as a damp course (overhanging the cavity wall by 5mm on the outside) the whole way around, and I'll put once weathered copings on top with the drips well clear etc. Does this sounds feasible, and would there still be a need to install cavity trays all the way around the parapet with weep holes to let any water out? I'm hoping if the inside face of the parapet is covered by the EPDM, the cavity trays won't be required? Thanks for any help you can give!
Cavity tray all the way round as a fail safe. Also I use insulated cavity closer and then dpc over the top and the. Edpm 100mm over install your coping stones and if it's your house get some sealer and paint the copings . We're it connects to the existing house get some lead flashing and beat it around the coping
When you install an EDPM roof that goes over the inner leaf and half way over the outer leaf, with coping stones supposed to be mechanically fixed how do you do this and still keep the integrity of the roof?
With difficulty from my understanding of the regulations you only have to mechanically fix coping if laid over 20 degrees
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