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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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  1.  
    Please could anyone advise? We are replacing our bathroom and would like to improve insulation in the process. We live in a solid wall 1930’s property. The bathroom has two external walls with sloped skeilings. We currently get a lot of condensation build up in the colder months after a showering, especially on the skeilings.

    We are thinking to ask the tiler/plasterer to dry-line the external walls with insulation board, as well as the skeilings (the flat part of the ceiling has a thick layer of loft insulation on it). Does this sound a good idea? Should we also dry-line the flat part of the ceiling and the internal walls as well?!

    Been reading others comments and now I’m worried about cold spots and interstitial condensation –any advice welcome, we have no expertise in building matters and are pretty baffled!! Thanks.
  2.  
    First thing - I always bang on about this! - you need Building Control approval, as you would be 'renovating' (adding or replacing a layer on) more than 50% of the external walls in a room. That means you will either need to improve the U value of the walls from the current 2.1W/m2K (or 1.7W/m2K depending on which version of SAP you look at) to 0.3W/m2K (about 65mm of Polyurethane - Pu), or you need to invoke one of the 'get-out clauses' (including the one about 'traditionally-built' buildings and breathability).

    I am much less comfortable with vapour-control methods of insulation than I am with breathable (water-vapour-permeable) ones, but you would want, for example, to think twice before using wood-fibre in a bathroom.

    If (as you should do) you are trying to get a really, really 'tight' vapour control layer (VCL), I would not recommend composite insulation/plasterboards, as you cannot guarantee the VCL on the joints. Use separate insulation boards and plasterboard instead.

    Enough for now, but plenty more help if you need it.
    • CommentAuthorslow
    • CommentTime6 days ago
     
    Several years ago I lined the bathroom upstairs in a solid brick Victorian terrace with insulating plasterboard (room too small for any other solution), using a thin adhesive over the entire sheet to stick it to the bricks. Unless any void is actually properly ventilated, the batten-off method allows a nasty black mould to develop in the void, because internal insulation often moves the dew point right in to the internal face of the external wall.

    I did the whole ceiling with insulated plasterboard too (flat area & sloped area). Since then I’ve repeated this on several properties, as the performance is great. As Nick Parsons points out above, this needs to be run past BC. I have never had any issues with tthe approach above, as they take the view that this is the most pragmatic solution in what is the small rear upstairs room, that in our Bristol terraces has two external walls and a shallow pitch roof void. I’ve solved mouldy, cold bathrooms & kids bedrooms in this same room this way, and BC have always been happy. I do provide them with dew point calcs, but they’re often less aware of options than any client that has done a bit of research.

    My preferred method, which I’ve done three times now to resolve cold rooms, is to add a hemp plaster at 25-30mm to the inner face of the external walls, insulated plasterboard to the ceiling, and paint them both with Earthborn claypaint. These rooms feel warmer (perception) than the plain insulated rooms, because the claypaint buffers the moisture levels suprisingly effectively, especially in bathrooms. I do also always put in a ventilation fan with a long run-on time, though.

    Have fun :)
    • CommentAuthortony
    • CommentTime6 days ago
     
    For me 80 or 90 mm insulated plasterboard foamed onto outside walls, insulate ceiling to a better standard then refit bathroom.
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