Hi Steve - been following you for a while now. I’m considering a roof structure like this one but with a 200mm soil turf layer on top on the GRP. Will this likely provide sufficient insulation to get round this problem. If not, I’ll check out the Siga system. Many thanks.
Thank you for your question. Unfortunately, I’m not qualified to make a definitive decision on this matter. In situations like this, an engineer would typically be responsible for designing the details, calculating insulation values, and assessing dew points to ensure the construction meets the required standards. There are two key challenges with this approach. Firstly, it can be difficult to find an engineer willing to take on this task, as it often falls outside their usual scope, and some may not have the necessary software. Additionally, many engineers are reluctant to provide such services because of the time involved and the possibility that they may need to charge a high fee, which can deter clients. Manufacturers often offer guidelines regarding their products, but when it comes to specifying a system that involves their products alongside others, they tend to avoid giving detailed design criteria. From a practical standpoint, the main question is whether any part of the internal structure will reach a temperature low enough to cause condensation on surfaces. Adding a 200mm layer of soil and turf on top of the GRP may help keep the internal surfaces warm enough to prevent condensation. However, it's important to note that this is only a possibility, and a proper design is necessary to ensure success. That said, I am personally not a fan of green roofs, which is essentially what you’re proposing. If you opt for a green roof, you must ensure that the roofing system underneath is absolutely bulletproof. This includes not only the main roofing material but also the surrounding edges, flashings, and outlets, as these are often the areas where leaks occur. Maintenance is another significant consideration. Over the roof’s lifespan (typically around 20 years), you’ll need to keep all the flashings and outlets in perfect condition. Any issues that arise, such as leaks, can lead to the costly and time-consuming process of removing the entire green roof for repairs, which can become a money pit. Many people who contact us about green roofs express regret due to the high maintenance costs and complexities involved.
@@SteveRoofer Many thanks for your generous and detailed reply steve. All points noted and understood. I’m going to do further research on this - in particular, how they construct these types of roofs in Norway and the Faroe Islands. I’m on an island in the Hebrides and surrounded by wonderful turf! 😁
Great information as always Steve. Can I ask, in regards to the dropped ceiling to accommodate lighting. Do you recommend this method for warm roofs too? Also how much of a drop do you recommend considering there may be water pipes as well as cables?
@@danthechippie4439 Surely you wouldn’t need a service void for a warm roof as you should have sufficient space within the rafter void to install any spot lights. Interesting to hear Steve’s thoughts though
No, you don't need a service void for a warm roof. The warm roof normally sits on joists, so the space between the joists is free to use for whatever you need. However, with a compact roof, you do need a service void, and the depth depends on what you want to put in there.
I’d really like to hear your thoughts and opinions on super foil and how it can be worked into a roof system with pir/rockwool between the rafters. I just cannot get my head around the u value calculation
Recently, I did some videoing for superfoil and I also did one or two roofs using it so I have some videos coming out regarding that product. Also I too have problems with you value calculations always best to get them to work it out however, when you are working with two or three different products, nobody wants to do the calculations.
@@SteveRoofer that’s exactly the problem, it just seems really complicated to get the right amount of insulation. I’ll be looking forward to your take on that tho, cheers mate
I thought the Vapour control layer was supposed to be on the warm side of the insulation, seems to show it sandwiched between the across joist and the under joist.
Thank you so much for your kind comment! I do carry out a lot of roof surveys, but I want to clarify that I'm not a qualified surveyor or a member of RICS (Royal Institution of Chartered Surveyors). My background comes from decades of hands-on experience in roofing and the broader building industry. Over the past 40 years, I've had the privilege of working alongside some incredibly skilled structural engineers and surveyors. Much like them, I've spent countless hours on-site, attending meetings and discussing solutions to complex problems.My focus has always been on retrofit and repair, which means I'm constantly dealing with real-world challenges and finding ways to solve them, which I find fascinating. This kind of problem-solving has naturally led me to where I am today, sharing insights through my videos.One of the things I've noticed over the past two decades of specialising in roofing is the lack of formal training available for roofers. While there is training for certain materials and specific techniques, there's really nothing comprehensive to help roofers stay updated with new specifications and industry standards. When my son-in-law, who came from the highly regulated aircraft industry, joined me after lockdown, he was shocked at how uncontrolled things seemed in the building trade.He came from a world where every nut, bolt, and washer had a track record, while in roofing, we don’t have anyting like that level of control. When I showed him the British Standards I use for reference-each one costing hundreds of pounds-he questioned why roofers don't have easy access to this information. And he’s right. Most roofers don't have access to these critical documents unless they invest the time, money, and effort themselves.This is likely why, in my experience, around 99.9% of new roofs I inspect aren't entirely correct. While many aren't critically wrong, most have errors, some of which can be quite significant. It’s part of why I’m passionate about sharing what I know-to bridge this gap and help improve standards where I can.Thanks again for watching and for considering my videos a form of CPD for surveyors. It means a lot!
Hi Steve, I'm just about to install a VCL in a timber frame garden room that has a warm roof construction with alutrix vapour barrier. Should I terminate the internal VCL at the top of the wall header, between the joists to the lower roof deck or completely cover the roof joists?
Hi Steve I'm enjoying all the videos you put up . I have a question for you , so I'm doing a small extension at the rear of property, we had a new metal tile effect roof fitted on to 4"X2" battons and they sit on the breathable sheeting , so the extension has to be flat and I only have 2170mm from floor to the metal roof overhang at eves , to get head height cold roof would suit ISH but I'm hoping if I can have a warm roof , as the extension width is only 2 MTRS could I get away with 4"X2" roof joists with insulation between them but attached to the underside of osb and a further insulation on top and sealed with liquid rubber , I'll also be using vapour barrier and also spots in ceiling ...eg Ceiling 12.5 mm Joists 100mm With insulation in top half of void 50mm Then osb then insulation with rubber liquid to seal Vapour barrier in-between ceiling and joist , Would this work , there are only us two so the kitchen and bathroom won't be over used . Also was talking to my father and he was saying that when he had his flat roof done in 90s they didn't use any insulation in-between joists or on top , and he never had any problems, even so I'm not thinking of going down this route .
Hi Steve, great videos as always! I was just wondering if there was a maximum cold roof vent space above the insulation? I know usually you say to have 50mm but would it be possible to increase this to 100 or even 150mm?
I have a loft conversion company and I am interested in using best possible insulation method for our clients We install 150 mm rafters fit 100mm pir between then a second layer below rafter running horizontal then tape all joints foil tapethen we install intello plus intelligent membrane then a 12.5 mm slab Question I have is it possible or right to put intello membrane between the the two layers or are we right installing underneath There is a cross vent of 50 mm Appreciate your help Love your channel Willie
Hi Steve, I would love to hear about doing an insulated concrete form (ICF) roof with the added functionality of walking on it and utilising that space to place things like solar panels, and even some furniture on it to enjoy the few good weather days. I would be curious if, for example, it would be good implementing a decking over the flat roof. Cheers!
If building control want to promote warm roofs then the 3mtr max height has be raised. If you add it up 150mm underfloor air space, 150mm floor joists, 22mm chip board flooring. 225mm joists + another >25mm furrings, chipboard roofing and covering. You have just about enough head room in the actual living space. Think what happens if you added another 150-200mm for a warm roof. Where is that space going to be taken from.
good point and they are relaxing it a little bit no one's actually putting a tape measure on it all the warm flat roofs that we actually do we ask the customer to ask planning if it's okay to do it because theoretically you are extending your property however if I come back and say no, you can't do it you could have an argument with them because the government want you to do it. They say you can't do it who's gonna win?
@@SteveRoofer Its all academic now for me as I went for a cold roof. But made sure there is proper ventilation from the fascia back to the house. As per another video you made I had to custom make the vent up against the wall.
Hi Steve - been following you for a while now. I’m considering a roof structure like this one but with a 200mm soil turf layer on top on the GRP. Will this likely provide sufficient insulation to get round this problem. If not, I’ll check out the Siga
system. Many thanks.
Thank you for your question. Unfortunately, I’m not qualified to make a definitive decision on this matter. In situations like this, an engineer would typically be responsible for designing the details, calculating insulation values, and assessing dew points to ensure the construction meets the required standards.
There are two key challenges with this approach. Firstly, it can be difficult to find an engineer willing to take on this task, as it often falls outside their usual scope, and some may not have the necessary software. Additionally, many engineers are reluctant to provide such services because of the time involved and the possibility that they may need to charge a high fee, which can deter clients.
Manufacturers often offer guidelines regarding their products, but when it comes to specifying a system that involves their products alongside others, they tend to avoid giving detailed design criteria.
From a practical standpoint, the main question is whether any part of the internal structure will reach a temperature low enough to cause condensation on surfaces. Adding a 200mm layer of soil and turf on top of the GRP may help keep the internal surfaces warm enough to prevent condensation. However, it's important to note that this is only a possibility, and a proper design is necessary to ensure success.
That said, I am personally not a fan of green roofs, which is essentially what you’re proposing. If you opt for a green roof, you must ensure that the roofing system underneath is absolutely bulletproof. This includes not only the main roofing material but also the surrounding edges, flashings, and outlets, as these are often the areas where leaks occur.
Maintenance is another significant consideration. Over the roof’s lifespan (typically around 20 years), you’ll need to keep all the flashings and outlets in perfect condition. Any issues that arise, such as leaks, can lead to the costly and time-consuming process of removing the entire green roof for repairs, which can become a money pit. Many people who contact us about green roofs express regret due to the high maintenance costs and complexities involved.
@@SteveRoofer Many thanks for your generous and detailed reply steve. All points noted and understood. I’m going to do further research on this - in particular, how they construct these types of roofs in Norway and the Faroe Islands.
I’m on an island in the Hebrides and surrounded by wonderful turf! 😁
hallejuja, somebody that actually understands, roof construction, insulation, ventilation and vapour control
Thanks
Great information as always Steve. Can I ask, in regards to the dropped ceiling to accommodate lighting. Do you recommend this method for warm roofs too?
Also how much of a drop do you recommend considering there may be water pipes as well as cables?
@@danthechippie4439 Surely you wouldn’t need a service void for a warm roof as you should have sufficient space within the rafter void to install any spot lights. Interesting to hear Steve’s thoughts though
No, you don't need a service void for a warm roof. The warm roof normally sits on joists, so the space between the joists is free to use for whatever you need. However, with a compact roof, you do need a service void, and the depth depends on what you want to put in there.
Well done Steve, concepts well explained with good diagrams.
Glad it was helpful!
Very interesting Steve, it makes a lot of sense, thanks for sharing🙏
Glad you enjoyed it
A pleasure to see such an informative video
thanks for the nice comment
Great video Steve. Would be keen to hear your thoughts about the various roofing systems ie single ply, GRP, EDPM, etc.
yes I've made a note of that and I think it is one I will do soon
I’d really like to hear your thoughts and opinions on super foil and how it can be worked into a roof system with pir/rockwool between the rafters. I just cannot get my head around the u value calculation
Recently, I did some videoing for superfoil and I also did one or two roofs using it so I have some videos coming out regarding that product. Also I too have problems with you value calculations always best to get them to work it out however, when you are working with two or three different products, nobody wants to do the calculations.
This is a rearly good site have a look tell me what you think www.ubakus.de/en/r-value-calculator/index.php?
@@SteveRoofer that’s exactly the problem, it just seems really complicated to get the right amount of insulation. I’ll be looking forward to your take on that tho, cheers mate
I thought the Vapour control layer was supposed to be on the warm side of the insulation, seems to show it sandwiched between the across joist and the under joist.
Unfortunately not all the time can you get it on the very warm side so a little bit inside of that i.e. 25 mm is not a problem
Love your videos, its CPD for surveyors
Thank you so much for your kind comment! I do carry out a lot of roof surveys, but I want to clarify that I'm not a qualified surveyor or a member of RICS (Royal Institution of Chartered Surveyors). My background comes from decades of hands-on experience in roofing and the broader building industry. Over the past 40 years, I've had the privilege of working alongside some incredibly skilled structural engineers and surveyors. Much like them, I've spent countless hours on-site, attending meetings and discussing solutions to complex problems.My focus has always been on retrofit and repair, which means I'm constantly dealing with real-world challenges and finding ways to solve them, which I find fascinating. This kind of problem-solving has naturally led me to where I am today, sharing insights through my videos.One of the things I've noticed over the past two decades of specialising in roofing is the lack of formal training available for roofers. While there is training for certain materials and specific techniques, there's really nothing comprehensive to help roofers stay updated with new specifications and industry standards. When my son-in-law, who came from the highly regulated aircraft industry, joined me after lockdown, he was shocked at how uncontrolled things seemed in the building trade.He came from a world where every nut, bolt, and washer had a track record, while in roofing, we don’t have anyting like that level of control. When I showed him the British Standards I use for reference-each one costing hundreds of pounds-he questioned why roofers don't have easy access to this information. And he’s right. Most roofers don't have access to these critical documents unless they invest the time, money, and effort themselves.This is likely why, in my experience, around 99.9% of new roofs I inspect aren't entirely correct. While many aren't critically wrong, most have errors, some of which can be quite significant. It’s part of why I’m passionate about sharing what I know-to bridge this gap and help improve standards where I can.Thanks again for watching and for considering my videos a form of CPD for surveyors. It means a lot!
Hi Steve, I'm just about to install a VCL in a timber frame garden room that has a warm roof construction with alutrix vapour barrier. Should I terminate the internal VCL at the top of the wall header, between the joists to the lower roof deck or completely cover the roof joists?
Hi Steve I'm enjoying all the videos you put up .
I have a question for you , so I'm doing a small extension at the rear of property, we had a new metal tile effect roof fitted on to 4"X2" battons and they sit on the breathable sheeting , so the extension has to be flat and I only have 2170mm from floor to the metal roof overhang at eves , to get head height cold roof would suit ISH but I'm hoping if I can have a warm roof , as the extension width is only 2 MTRS could I get away with 4"X2" roof joists with insulation between them but attached to the underside of osb and a further insulation on top and sealed with liquid rubber , I'll also be using vapour barrier and also spots in ceiling ...eg
Ceiling 12.5 mm
Joists 100mm
With insulation in top half of void 50mm
Then osb then insulation with rubber liquid to seal
Vapour barrier in-between ceiling and joist ,
Would this work , there are only us two so the kitchen and bathroom won't be over used .
Also was talking to my father and he was saying that when he had his flat roof done in 90s they didn't use any insulation in-between joists or on top , and he never had any problems, even so I'm not thinking of going down this route .
Hi Steve, great videos as always! I was just wondering if there was a maximum cold roof vent space above the insulation? I know usually you say to have 50mm but would it be possible to increase this to 100 or even 150mm?
I have a loft conversion company and I am interested in using best possible insulation method for our clients
We install 150 mm rafters fit 100mm pir between then a second layer below rafter running horizontal then tape all joints foil tapethen we install intello plus intelligent membrane then a 12.5 mm slab
Question I have is it possible or right to put intello membrane between the the two layers or are we right installing underneath
There is a cross vent of 50 mm
Appreciate your help
Love your channel
Willie
Hi Steve, I would love to hear about doing an insulated concrete form (ICF) roof with the added functionality of walking on it and utilising that space to place things like solar panels, and even some furniture on it to enjoy the few good weather days. I would be curious if, for example, it would be good implementing a decking over the flat roof. Cheers!
Great suggestion!
Where from this Siga CAD detail? Cannot find it on their site
Search for compact flat roof in their blog
@@SteveRoofer
Thank you. By the way, And may I ask your opinion on notorious professor Lstiburek's The Perfect Wall/Roof concept?
@@Darrida I think he is amazing. Why do you call him notorious?
@@SteveRoofer
Lots of bloggers link to his articles
Warmish moist air trickles into vent space during the day, then at night it's colder and it condenses
If building control want to promote warm roofs then the 3mtr max height has be raised. If you add it up 150mm underfloor air space, 150mm floor joists, 22mm chip board flooring. 225mm joists + another >25mm furrings, chipboard roofing and covering. You have just about enough head room in the actual living space. Think what happens if you added another 150-200mm for a warm roof. Where is that space going to be taken from.
good point and they are relaxing it a little bit no one's actually putting a tape measure on it all the warm flat roofs that we actually do we ask the customer to ask planning if it's okay to do it because theoretically you are extending your property however if I come back and say no, you can't do it you could have an argument with them because the government want you to do it. They say you can't do it who's gonna win?
@@SteveRoofer Its all academic now for me as I went for a cold roof. But made sure there is proper ventilation from the fascia back to the house. As per another video you made I had to custom make the vent up against the wall.
@@logik100.0 Sounds like you had the same problems as I had & ended up building the same thing as I did.
👍👍
Thanks