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Insulate sloping ceilings

Discussion in 'Roofing and Guttering' started by selfbuildextension, 26 Nov 2018.

  1. selfbuildextension

    selfbuildextension

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    Hi,

    My upstairs bedrooms all feature a 1.5m section of sloping ceiling from the outside wall before turning to a normal flat ceiling. It's a 1930's semi and i presume there is no insulation between the sloping ceiling and the roof. This section of ceiling is much colder to touch. I am going to lay new insulation in the loft, but how do i deal with the sloped part?

    The ceilings are covered in cracks so no issues stripping them but I don't want to introduce any condensation/damp issue.

    Thanks
     
  2. Alastairreid

    Alastairreid

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    You can use insulated plasterboard fixed to the existing ceiling, or remove the lath and plaster and insulate between the rafters.
     
  3. noseall

    noseall

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    Do both or you risk rafter 'shadowing' occurring. Make sure there is an air gap above the insulation (cold side) if you do decide to go between the rafters and robustly introduce vapour control measures.
     
  4. selfbuildextension

    selfbuildextension

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    Thanks for the replies.

    So I could batten to leave a gap and put as thick as possible insulation between rafters then insulated plasterboard fixed to the rafters and skimmed.

    Would I put a vapour control membrane after the rafter insulation but before the insulated plasterboard?

    Thanks,

    Shaun
     
  5. catlad

    catlad

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    Once you have fitted the kingspan between the rafters you can buy 100mm foil tape or staple a vapour barrier
    to the rafters prior to insulated plasterboard.
     
  6. noseall

    noseall

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    You are much better off installing them as separates - i.e. fix a sheet of insulation across the rafters then a sheet of plasterboard. It means you can use foil sandwich Celotex type insulation board which can be foil taped. You can then use foil backed plasterboards.
     
  7. DIYnot Local

    DIYnot Local

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