Loft conversion; extra insluation below rafters for thermal bridging ?

Discussion in 'Eco Talk' started by heathrow, Dec 16, 2017.

  1. heathrow

    heathrow New Member

    Hi there

    What would you do ?

    We have 150mm celotex in between rafters. Building control are happy with this amount of insulation so we can just board over the rafters.

    however, i am reading a lot about thermal bridging from the rafters and celotex recommend boarding with insulated plasterboard to mitigate this. is this just a selling ploy? I understand the theory but really will it matter at the end of the day?

    If we go with the insulated plasterboard it will cost and this will reduce our ceiling height; the bedrooms are small enough as it is with a large amount of sloping ceiling.

    Will there be condensation problems on the plastered surface where the rafters are behind the plasterboarding if we don't?

    Advice appreciated. Thanks
  2. KIAB

    KIAB Well-Known Member

    Got a photo, how large is sloped

    Always insulate eaves, insulated plasterboard doesn't have to be that thick,Gyproc Thermaline Insulated Plasterboard is only 22mm, but thermal bridging at eaves, you'll most likely end up with condensation & mould.

    There is a good thead on this forum, covering same subject earlier this year I think.
    Last edited: Dec 16, 2017
  3. KIAB

    KIAB Well-Known Member

  4. heathrow

    heathrow New Member

    Hi KIAB
    Thanks for finding that thread and also your reply.

    I will definately attend to insulating around the wall plate area, if that is what you meant by "the eaves". The celotoex in the rafters is going right down to the wall plate, which is behind the "dwarf wall" vertical timbers of the prefab roof trusses . And we will probably stuff in some extra in the corner. I think the eaves will be used for storage. i guess it would not hurt height wise to use insulated plasterboard under the rafters in that storage area as a minimum.

    thanks for your advice. i am considering doing the whole lot with insualated pb

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