Gaf Posted January 19 Share Posted January 19 New build. It's a 1.5 story so the first floor has all pitched roofs. Construction drawings specified Kingspan Kooltherm K7 Pitched Room Board over rafters and between rafters. Builder has stated a preference to use open cell spray foam in these areas instead of the boards. Mentioned it's both a labour cost saving and he said realistically there will be gaps in the boards no matter how skilled the installer is. Said the open cell will match the same required U-value as stated on the construction drawings. Curious about others opinions on either approach. I've read the spray foam can be prohibitive in therms of having no way to identify any issues with the woods in the trusses etc. This might be overkill and OTT, but we had a bad experience with asbestos in a ceiling before and I am slightly put off from the spray foam because I just don't like the idea of having a material that down the line could cause issues if we wanted it removed (I know it's nothing at all like asbestos, so this probably sounds like a completely idiotic thing to be concerned about). House is in Rep. of Ireland and there are currently none of the mortgage concerns with the spray insulation at present. It's also not a house we plan to ever sell. Link to comment Share on other sites More sharing options...
JohnMo Posted January 19 Share Posted January 19 We did open cell foam. You need a vapour control layer inside (fully taped) inside and a breather membrane to the outside. Our roof had sarking boards and the membrane the breather membrane above. Don't believe the hype saying it's airtight - because it isn't. Get an interstitial condensation report done prior to agreement. At least you have the paperwork to say there is no issues with the design. Mortgage issue is a different thing anyway. That is mostly a bodge done with a vapour closed foam, to make a poor roof seem good. 1 Link to comment Share on other sites More sharing options...
crispy_wafer Posted January 19 Share Posted January 19 1 hour ago, Gaf said: New build. It's a 1.5 story so the first floor has all pitched roofs. Construction drawings specified Kingspan Kooltherm K7 Pitched Room Board over rafters and between rafters. Builder has stated a preference to use open cell spray foam in these areas instead of the boards. Mentioned it's both a labour cost saving and he said realistically there will be gaps in the boards no matter how skilled the installer is. Said the open cell will match the same required U-value as stated on the construction drawings. Curious about others opinions on either approach. I've read the spray foam can be prohibitive in therms of having no way to identify any issues with the woods in the trusses etc. This might be overkill and OTT, but we had a bad experience with asbestos in a ceiling before and I am slightly put off from the spray foam because I just don't like the idea of having a material that down the line could cause issues if we wanted it removed (I know it's nothing at all like asbestos, so this probably sounds like a completely idiotic thing to be concerned about). House is in Rep. of Ireland and there are currently none of the mortgage concerns with the spray insulation at present. It's also not a house we plan to ever sell. is a SIPS roof an option? Is this an imminent decision, or can you stall for a bit of time whilst you do a bit of research? Link to comment Share on other sites More sharing options...
ETC Posted January 19 Share Posted January 19 DO NOT USE SPRAY FOAM INSULATION. JUST DON’T. Link to comment Share on other sites More sharing options...
Iceverge Posted January 19 Share Posted January 19 3 hours ago, Gaf said: New build. It's a 1.5 story so the first floor has all pitched roofs. Construction drawings specified Kingspan Kooltherm K7 Pitched Room Board over rafters and between rafters. Builder has stated a preference to use open cell spray foam in these areas instead of the boards. Mentioned it's both a labour cost saving and he said realistically there will be gaps in the boards no matter how skilled the installer is. Said the open cell will match the same required U-value as stated on the construction drawings. Curious about others opinions on either approach. I've read the spray foam can be prohibitive in therms of having no way to identify any issues with the woods in the trusses etc. This might be overkill and OTT, but we had a bad experience with asbestos in a ceiling before and I am slightly put off from the spray foam because I just don't like the idea of having a material that down the line could cause issues if we wanted it removed (I know it's nothing at all like asbestos, so this probably sounds like a completely idiotic thing to be concerned about). House is in Rep. of Ireland and there are currently none of the mortgage concerns with the spray insulation at present. It's also not a house we plan to ever sell. The Kingspan Salesman gets another set of new gold plated golf clubs! Such laziness by design professionals to just copy and paste a commercial companies detail and unquestioning pass it onto the customer. Correctly done I'd have no issue with spray foam. 2 hours ago, JohnMo said: Don't believe the hype saying it's airtight - because it isn't. It depends on the situation. @Gone West got passivhaus airtightness just with open cell foam on his first house but there was 300mm+ of it. However. I'd just use blown cellulose. I'm a big fan. Great for ease of install, airtightness, decrement delay (summer heat protection), fire performance, off gassing, emboddied carbon, noise isolation. Here's a very buildable detail. 1 Link to comment Share on other sites More sharing options...
Temp Posted January 19 Share Posted January 19 (edited) There should be no issues with fitting the layer of boards above the rafters. These can be butted together and joints taped. Over these boards there should be a membrane and counter battens parallel with the rafters. Regular horizontal battens go on to of these. This construction is known as a warm roof (not to be confused with a warm loft). It's what I would build if building again but not all builders are familiar with this approach. It is quite a bit of work to fit boards between the rafters but my builder didn't complain and I bet my roof is more complicated. Edited January 19 by Temp 3 Link to comment Share on other sites More sharing options...
Gone West Posted January 20 Share Posted January 20 13 hours ago, Gaf said: Construction drawings specified Kingspan Kooltherm K7 Pitched Room Board over rafters and between rafters. Builder has stated a preference to use open cell spray foam in these areas instead of the boards. Mentioned it's both a labour cost saving and he said realistically there will be gaps in the boards no matter how skilled the installer is. Said the open cell will match the same required U-value as stated on the construction drawings. 12 hours ago, JohnMo said: We did open cell foam. You need a vapour control layer inside (fully taped) inside and a breather membrane to the outside. Our roof had sarking boards and the membrane the breather membrane above. Don't believe the hype saying it's airtight - because it isn't. We built a timber I-beam portal frame house with 350mm I-beams and external 15mm OSB3 racking. The walls and roof had 350mm Icynene between the I-beams and 50mm Rockwool on the outside of the racking. We had interstitial condensation analysis carried out during the design stage and didn't use any airtightness or vapour membranes. We also didn't use any airtightness tapes in the house and achieved an average airtightness of 0.47ACH. Link to comment Share on other sites More sharing options...
nod Posted January 20 Share Posted January 20 11 hours ago, ETC said: DO NOT USE SPRAY FOAM INSULATION. JUST DON’T. 👏 👏 Finally It is dog 💩 Link to comment Share on other sites More sharing options...
SteamyTea Posted January 20 Share Posted January 20 (edited) No matter how well foam is sprayed onto a roof, and no matter what type of foam is used, insurance companies and money lenders will walk away from it. @joe90 did a warm roof at his place, don't know the details but when I was in his loft once, it was not too warm (was a hot day), so must have been working. Edited January 20 by SteamyTea Link to comment Share on other sites More sharing options...
Iceverge Posted January 20 Share Posted January 20 42 minutes ago, SteamyTea said: @joe90 did a warm roof at his place, don't know the details but when I was in his loft once, it was not too warm (was a hot day), so must have been working. ........brain search engine tells me it was rockwool batts between I Joists and lots of Illbruck FM330 and OSB as an airtightness measure..... 1 Link to comment Share on other sites More sharing options...
saveasteading Posted January 20 Share Posted January 20 48 minutes ago, SteamyTea said: was not too warm (was a hot day), so must have been working That's different from keeping heat inside. The sun hits the roof and heats the slates/ steel/ whatever and a lot radiates off or ventilates especially with a ventilation gap. Only what remains can try to wiggle through the insulation before night time cooling. Link to comment Share on other sites More sharing options...
joe90 Posted January 20 Share Posted January 20 Well remembered @Iceverge, simply put, insulation works both ways, why a thermos can keep drinks cool as well as hot🤷♂️ Link to comment Share on other sites More sharing options...
Alan Ambrose Posted January 20 Share Posted January 20 @Iceverge - with your stack-up above - do you need another layer of osb behind the inner vapour retarder or is the vapour retarder itself enough to keep the cellulose in place? Link to comment Share on other sites More sharing options...
Gaf Posted January 21 Author Share Posted January 21 Cheers for all the replies. Looks like lots of different ways to do this. On 19/01/2024 at 19:57, JohnMo said: We did open cell foam. You need a vapour control layer inside (fully taped) inside and a breather membrane to the outside. Our roof had sarking boards and the membrane the breather membrane above. Don't believe the hype saying it's airtight - because it isn't. Get an interstitial condensation report done prior to agreement. At least you have the paperwork to say there is no issues with the design. Mortgage issue is a different thing anyway. That is mostly a bodge done with a vapour closed foam, to make a poor roof seem good. Thanks for the reminder on the condensation report. We got one done for the original architect's spec but would have to get a new one for the spray foam. On 19/01/2024 at 22:49, Iceverge said: The Kingspan Salesman gets another set of new gold plated golf clubs! Such laziness by design professionals to just copy and paste a commercial companies detail and unquestioning pass it onto the customer. Correctly done I'd have no issue with spray foam. It depends on the situation. @Gone West got passivhaus airtightness just with open cell foam on his first house but there was 300mm+ of it. However. I'd just use blown cellulose. I'm a big fan. Great for ease of install, airtightness, decrement delay (summer heat protection), fire performance, off gassing, emboddied carbon, noise isolation. Cheers for suggestion. At this point I feel a bit piggy in the middle with architect suggesting one approach and builder suggesting the other. Conscious I haven't a fiddlers about any of this stuff and need to lean on their expertise. With the Kingspan, do you mean the architect has just taken kingspan's description of how to use their product and passed this 'design' onto us? On 19/01/2024 at 23:30, Temp said: There should be no issues with fitting the layer of boards above the rafters. These can be butted together and joints taped. Over these boards there should be a membrane and counter battens parallel with the rafters. Regular horizontal battens go on to of these. This construction is known as a warm roof (not to be confused with a warm loft). It's what I would build if building again but not all builders are familiar with this approach. It is quite a bit of work to fit boards between the rafters but my builder didn't complain and I bet my roof is more complicated. I'm inclined towards sticking with the architect's construction drawing specification. I'm going to touch base with him about the builder's preference but reckon I'll go with the non-spray foam approach, even if it adds additional cost. Link to comment Share on other sites More sharing options...
Iceverge Posted January 22 Share Posted January 22 @Gaf Can you post up a cross section of your house please? Take your name and address off it and I'll have a look. Kingspan Kooltherm is ridiculously expensive. It's 4 times dearer than PIR for the same U value and 7 times the price of mineral wool. It has a negligible performance increase for the same thickness vs other insulations. 100mm Kooltherm is the same as 105mm of PIR. There's two reason's the architect is suggesting it. The Kingspan salesman gave them a handy booklet that they were able to copy and paste a detail into your drawing because they were too lazy to cost and draw up a detail themselves. The Architect is getting commission from Kingspan for selling their product. Either way it's going to cost you thousands of euro. 1 Link to comment Share on other sites More sharing options...
SteamyTea Posted January 22 Share Posted January 22 22 hours ago, Gaf said: I'm inclined towards sticking with the architect's construction drawing specification. Their insurance is probably better, and they will be properly qualified, unlike a lot of builders. Link to comment Share on other sites More sharing options...
saveasteading Posted January 22 Share Posted January 22 4 hours ago, SteamyTea said: they will be properly qualified, unlike a lot of builders. So will professionally accept your instruction to save lots of your money by changing the spec Link to comment Share on other sites More sharing options...
Gaf Posted January 22 Author Share Posted January 22 (edited) @Iceverge Cross section attached with identifiers removed. Cheers for having a look. Take your point re: Kingspan. Welcome any thoughts and alternatives to the Kingspan. Edited January 23 by jack Image removed as requested Link to comment Share on other sites More sharing options...
Iceverge Posted January 22 Share Posted January 22 Yup, kingspan galore. If you want to do the calcs on the U values,the drawing is optimistic with its numbers too. I make the floor 0.174W/m2K The walls are 0.163W/m2K the pitched roof is 0.196W/m2k The roof on flat is 0.167. My suggestion. 150mm PIR in the floor for 0.16 or 200mm EPS. 200mm eps blown beads in a wider cavity and ditch the insulated plasterboard but use wet plaster finish inside instead. 220mm blown cellulose between rafters and a 47mm insulated service cavity below with mineral wool batts for 0.153W/m2K as shown above. 400mm blown cellulose on the flat above the central section for a U Value of about 0.12W/m2K. 1 Link to comment Share on other sites More sharing options...
crispy_wafer Posted January 22 Share Posted January 22 1 hour ago, Gaf said: alternatives to the Kingspan. PIR, refer to as what it is, rather than brand, or the builders merchants will have your pants down. 1 Link to comment Share on other sites More sharing options...
Gaf Posted January 23 Author Share Posted January 23 @Iceverge Unfortunately we're well down the line with the process that we would delay the start by months to go 200mm cavity. The architect has said he won't sign off on changing the 150mm to 200m, and we'd have to get the whole set of construction drawings redone plus wait an age for the construction engineer to do his bit on them. It's been a bit frustrating navigating the heat insulation aspects as everyone we spoke to said to do it differently. We ended up settling on what's in the drawings based on talking to four different builders in the area who said that's how they build 99% of their houses. Link to comment Share on other sites More sharing options...
SteamyTea Posted January 23 Share Posted January 23 1 minute ago, Gaf said: who said that's how they build 99% of their houses What do they do on the other 1%, not bother at all. Link to comment Share on other sites More sharing options...
Iceverge Posted January 23 Share Posted January 23 I imagine the architect drew up the houses for those builders. In any case, your house, your money, you are the boss. Assume you're stuck with the 150mm cavity with EPS blown beads and a fine pencil you'll scrape the 0.21W/m2K backstop for Part L of the building regs. Assuming you can compensate elsewhere with increased insulation then you could wet plaster internally. Vastly superior to insulated plasterboard for airtighess and cost. (Airtighess is much more important to insulation for comfort and energy bills) Here's a suggestion. Outside to inside. 20mm sand cement plaster. 100mm 13N dense concrete blocks. 150mm EPS blown beads with stainless steel cavity ties. 100mm 13N dense concrete blocks. 12mm sand cement plaster 3mm skim coat. U-Value 0.21 Then bump the floor to 200mm PIR or 300mm EPS. Top to bottom. 100mm fiber reinforced power floated concrete slab with UFH pipes stapled to insulation. Slip membrane. 100mm EPS. Radon membrane 200mm EPS. Get your truss supplier to supply trusses with 300mm thick rafters. Sloped ceiling from outside to inside. Slates Slate battens Counter battens 11mm OSB racking 300mm blown cellulose or mineral wool between the rafters. Airtighness membrane 47mm counter batten with mineral wool batts for service cavity. Plasterboard Skim. 1 Link to comment Share on other sites More sharing options...
Gaf Posted January 24 Author Share Posted January 24 @SteamyTea From four builders I spoke with (though I think it could have been even more) as well as two building surveyors and two BER guys, all said that all houses in the county/region go with 150mm cavity and IWI - just seems to be the done thing locally. Only one builder said he'd done an EWI build and he said it was the only one he'd ever done. @Iceverge The architect originally proposed full 215mm single leaf with EWI. Estimated costs for the EWI pushed us way out of budget and the recommended builders had pretty much no experience with this approach. Cheers for the suggestions. Forgive my ignorance on this - from what I can see in the 2022 Part L regulation, the maximum wall u-value allowable is 0.18. Is it the case that by bumping up the insulation in other parts of the house that this can compensate for the higher 0.21 u-value in the walls, so there's an acceptable 'average' u-value for the entire fabric of the house? I'm tempted to touch base with a couple of SEs to see what their availability is to maybe look at adjusting the drawings to 200mm and leave off the IWI. I might not survive though if herself learns of it 😆 Link to comment Share on other sites More sharing options...
Iceverge Posted January 24 Share Posted January 24 10 minutes ago, Gaf said: Cheers for the suggestions. Forgive my ignorance on this - from what I can see in the 2022 Part L regulation, the maximum wall u-value allowable is 0.18. Is it the case that by bumping up the insulation in other parts of the house that this can compensate for the higher 0.21 u-value in the walls, so there's an acceptable 'average' u-value for the entire fabric of the house? My mistake, you're absolutely correct. Regs have been updated since our house. 200mm cavities are very usual in our area (Cork). 12 minutes ago, Gaf said: tempted to touch base with a couple of SEs to see what their availability is to maybe look at adjusting the drawings to 200mm and leave off the IWI. I might not survive though if herself learns of it 😆 Maybe wise! 1 Link to comment Share on other sites More sharing options...
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