IanMcP Posted August 24, 2022 Share Posted August 24, 2022 Hey I have 4 mono pitch roofs. 2 with loft , 2 will be up to the rafters. trying to find a detail for the make up to allow spray foam - for insulation and air tight at the wall junction. House is ICF so air tight paramount. Rafters are web joists. 18mm deck above with green coat standing seam. looking at Isothane but they don’t supply and detail just tell me the depth needed for u value. does anybody have drawings to share please ? thanks Link to comment Share on other sites More sharing options...
JohnMo Posted August 24, 2022 Share Posted August 24, 2022 Mine is as follows Pitched roof Slate Breather membrane 22mm Sarking boards 256mm posi rafters - under drawn with 100mm battening, full filled with spray foam. VCL airtighness layer, double side tape and stapled to battens, fully taped and glued to wall 50mm service battens Plasterboard 12 degree roof Same except, mechanically fixed EPMD membrane with fleece below, breather membrane and 18mm plywood - everything else as above. Link to comment Share on other sites More sharing options...
Temp Posted August 24, 2022 Share Posted August 24, 2022 Sorry if you already know this but.. Right now there is an issue with mortgage lenders refusing mortgages on houses with spray foam in the roof. Its not clear if they have a blanket ban or if they get their surveyor to check it has/hasnt been correctly installed. https://www.mortgagesolutions.co.uk/news/2021/12/21/rpsa-warns-250000-homes-could-be-unmortgageable-due-to-spray-foam-insulation/ Quote According to an investigation by Residential Property Surveyors Association (RPSA) and Property Care Association (PCA), said that it had “failed to identify any circumstances” where a roof with this insulation could be given a “clean bill of health”. I would think it worth getting an independent nterstitial condensation risk report done on the proposed design just in case its an issue in the future. Link to comment Share on other sites More sharing options...
saveasteading Posted August 24, 2022 Share Posted August 24, 2022 18 minutes ago, Temp said: refusing mortgages on houses with spray foam With good reason. Not a good idea. Try finding a recognised builder who does it, and wonder why they don't. Link to comment Share on other sites More sharing options...
IanMcP Posted August 25, 2022 Author Share Posted August 25, 2022 Wasn’t aware no. Thank you. so spray foam is a no then… was exploring it for best air tight seal Suggestions welcome Link to comment Share on other sites More sharing options...
JohnMo Posted August 25, 2022 Share Posted August 25, 2022 The issue with spray foam, is when it's applied to roof in the incorrect manner. Ie normal cold roof space, then spraying in the back of the roof tiles, closing all the required ventilation. Mine was applied by a recognised builder. But what ever system you go for, you need to an interstitial condensation analysis. Link to comment Share on other sites More sharing options...
IanMcP Posted August 25, 2022 Author Share Posted August 25, 2022 Any recommendations ? Link to comment Share on other sites More sharing options...
JohnMo Posted August 25, 2022 Share Posted August 25, 2022 Whatever the insulation you use you will be installing a Vapour control air tightness layer below it. This is draped on to the wall internally and glued or taped to the wall.. That is is your airtightness sorted. Then use whatever insulation to the required U value. Link to comment Share on other sites More sharing options...
Temp Posted August 25, 2022 Share Posted August 25, 2022 8 hours ago, JohnMo said: The issue with spray foam, is when it's applied to roof in the incorrect manner. Ie normal cold roof space, then spraying in the back of the roof tiles, closing all the required ventilation. Also spraying onto the underside of non vapour permeable membranes. Link to comment Share on other sites More sharing options...
JohnMo Posted August 25, 2022 Share Posted August 25, 2022 Basically doing a bodge job, while demanding money to do so. Interesting the article refenced specifically states polyurethane foam. The foam mentioned at the start of the thread is a polyurethane, while something like Icynene isn't. Its cater oil and water based that open cell and quite soft and flexible compared to polyurethane foam, which is quite rigid. Link to comment Share on other sites More sharing options...
SteamyTea Posted August 27, 2022 Share Posted August 27, 2022 On 25/08/2022 at 16:32, JohnMo said: The foam mentioned at the start of the thread is a polyurethane, while something like Icynene isn't. Its cater oil and water based that open cell and quite soft and flexible compared to polyurethane foam, which is quite rigid. My sofa cushions are polyurethane foam, they are not rigid. The dashboard in many cars are polyurethane and is semi rigid, and integral skin. Water is what makes most PUs foam (blowing agent), melamine is added for fire performance. PUs have been made from plant based polyol for decades, but most is mineral oil based. Link to comment Share on other sites More sharing options...
JohnMo Posted August 27, 2022 Share Posted August 27, 2022 But I wasn't talking about your sofa or your dashboard I was specifically talking about spray foam insulation. Which isn't seat foam. Link to comment Share on other sites More sharing options...
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