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  • How important is a vapour barrier in a timber wall ?
  • I haven’t got any pictures, so I’ll have ago at describing it with words.

    150×50 vertical studs, with 50×50 horizontal noggins level with the outside face of the studs.
    The plan is to use 100mm Kingspan insulation level with the inside face of the studs and the inner face of the noggins, leaving a 50mm air gap between the noggins.
    19mm T&G set vertically on the outside and nailed to the noggins. This stuff is dual sided. One side is flat with chamfered edges like a heavy duty matchboard, the other is shiplap. I’ll be using it with the flat side outwards, so the scallops of the shiplap will create a small clear air space between the cladding and the noggins.

    So, do I need the 50mm air gap, or could I use 150mm insulation ?
    Do I need a vapour barrier between the cladding and noggins to keep the rain out while allowing vapour to escape ?

    I’ve got no plans to fit central heating if that makes a difference. There’s just a log burner in the living room and that’s it.

    neallyman
    Free Member

    Breather membrane and vapour barrier are 2 different things.
    Breather membrane on the outer side of the timber frame. Vapour barrier on the inner side of the timber frame to stop internal air moisture reaching the insulation (moisture stops it working so well).

    And, yes, I’d keep the 50mm air space.

    matt_outandabout
    Full Member

    Or look at http://www.natural-building.co.uk and ignore odd UK approach to building with membranes and like…breathing wall innit.

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    Whoops, yes, I meant breather membrane. 😳

    This stuff.

    Does it really do anything ?
    Is it just a second line of defence if the rain gets through the cladding ?
    Won’t it just run down the back of the cladding anyway ? It won’t damage the Kingspan.

    Matt, I’ll read that later, I’m off out now. I see there’s a criticism of Kingspan on there though.

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