Huckleberrys Posted April 22, 2023 Share Posted April 22, 2023 Hi. I am soon to be undertaking a small barn conversion. I am just in the process of sorting some bits out. In the loft I will be having fibreglass insulation...would it be good practice to provide a windproof membrane on the underside of the the rafters so I don't have wind blowing up and over the top of the insulation? Link to comment Share on other sites More sharing options...
Iceverge Posted April 22, 2023 Share Posted April 22, 2023 What is your roof construction as is? It's easier to tape a suitable breathable roofing membrane above the rafters. Link to comment Share on other sites More sharing options...
joe90 Posted April 22, 2023 Share Posted April 22, 2023 3 hours ago, Huckleberrys said: Hi. I am soon to be undertaking a small barn conversion. I am just in the process of sorting some bits out. In the loft I will be having fibreglass insulation...would it be good practice to provide a windproof membrane on the underside of the the rafters so I don't have wind blowing up and over the top of the insulation? I once read (but not seen since) that paper or similar laid between layers of fibreglass insulation stops wind/air washing between the layers giving better insulation performance . Link to comment Share on other sites More sharing options...
Iceverge Posted April 22, 2023 Share Posted April 22, 2023 https://www.eco-home-essentials.co.uk/how-to-install-insulation.html There's some reference to this method from this company. Link to comment Share on other sites More sharing options...
Huckleberrys Posted April 22, 2023 Author Share Posted April 22, 2023 (edited) It had a new roof put on 12 years ago. Slate, baton, membrane, rafter, purlin, a frame. I was thinking about putting some membrame under the rafter so the rafter depth would be a ventilated void but then wind proof the area insulated then air tight under insulation. Edited April 22, 2023 by Huckleberrys Spelling Link to comment Share on other sites More sharing options...
Radian Posted April 22, 2023 Share Posted April 22, 2023 28 minutes ago, Huckleberrys said: It had a new roof put on 12 years ago. Slate, baton, membrane, rafter, purlin, a frame. I was thinking about putting some membrame under the rafter so the rafter depth would be a ventilated void but then wind proof the area insulated then air tight under insulation. It's still a gamble if you get condensation or not. If this happens the main loft space won't be adequately vented. Link to comment Share on other sites More sharing options...
Iceverge Posted April 22, 2023 Share Posted April 22, 2023 How good is the vapour control layer below the insulation going to be? There's a risk with this approach if you don't get it 100%. We have a sealed cold attic as per the TYVEK detail and the attic has zero condensation but I did the airtight/vapour control membrane myself and got it (and tested it) to zero leaks. Link to comment Share on other sites More sharing options...
Huckleberrys Posted April 23, 2023 Author Share Posted April 23, 2023 Vapour control layer should be good...I will be doing it myself. Will also have mvhr. Link to comment Share on other sites More sharing options...
Iceverge Posted April 23, 2023 Share Posted April 23, 2023 Use a suitable breathable membrane then and go for it I say. Don't forget about the airtight attic hatch. Link to comment Share on other sites More sharing options...
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