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Attic conversion vs air tightness

  • 17-06-2020 10:28pm
    Registered Users Posts: 7 ✭✭✭ yulasinio

    First off a big hello to everyone. First time poster long time lurker :)

    We are looking to get some opinions from the experts on the board regarding attic conversion in an air thigh house.

    Our house is built using single hollow cement block capped on the outside with 150mm insulation. The house is airtight with mechanical extract ventilation.
    For those of you interested in details you can find a nice blog below which describes in more detail how the house was built.

    We would like to increase the house space by converting the attic and creating another bedroom and a small en-suite. I do worry about breaking the membrane that was laid over the whole house but I said I'll ask the pro's and send a few emails around for quotes.
    The first builder to respond asked a bunch of questions about the house was built etc. When finding out the house is air tight he said not to bother with the conversion as breaking the membrane will loose the BER certificate ratting and cause issues when selling the house. He also said the attic can be converted and preserve the air tightness but it will cost significantly more.

    I would like to hear other opinions from people on here. Is this really not doable and we should forget about it? The other option is to build a garden room which I think will be in around the same money.



  • Moderators, Home & Garden Moderators Posts: 10,094 Mod ✭✭✭✭ BryanF

    Julian everything is possible. Did the builder offer an extra over cost associated with providing air-tightness measures? Btw the way this has always been a requirement of building regulations under the guise of vapour barrier & avoidance of moisture from internal spaces to the fabric of the building.

  • Registered Users Posts: 7 ✭✭✭ yulasinio

    Thanks for you reply Bryan.
    No, didn't get a price for it to be done 'proper', sounded like he didn't wanted the hassle.
    I know everything is possible if the price is right :) Can the "bubble" be extended over the new stairs and the attic room to preserve the airtightness?

  • Moderators, Home & Garden Moderators Posts: 10,094 Mod ✭✭✭✭ BryanF