April 22, 20233 yr 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?
April 22, 20233 yr What is your roof construction as is? It's easier to tape a suitable breathable roofing membrane above the rafters.
April 22, 20233 yr 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 .
April 22, 20233 yr https://www.eco-home-essentials.co.uk/how-to-install-insulation.html There's some reference to this method from this company.
April 22, 20233 yr Author 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, 20233 yr by Huckleberrys Spelling
April 22, 20233 yr 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.
April 22, 20233 yr 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.
April 23, 20233 yr Author Vapour control layer should be good...I will be doing it myself. Will also have mvhr.
April 23, 20233 yr Use a suitable breathable membrane then and go for it I say. Don't forget about the airtight attic hatch.
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