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Hybrid warm roof U value calculator.

Discussion in 'Building Regulations and Planning Permission' started by rssteve, 6 Nov 2016.

  1. rssteve

    rssteve

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    Are there any hard set rules when dealing with hybrid warm roofs? I'm looking at a future extension and need to keep the roof level as low as possible. Don't want a cold roof though as want to fit down lighters, roof light and also a terrace area on the top. Also got to really keep the roof level with the garage flat roof.

    I've seen insulation values of 80mm on top and 40mm between the joist, but can't find a calculator that will deal with hybrids. Does the insulation on top have to be greater than below, or could I go with 70mm and 70mm for instance?

    The other idea to reduce height would be to increase joist width which would allow me to drop from 170 to 145mm joists, but I'm guessing that then I will need to increase insulation to make up for the increased thermal bridge.
     
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  3. tony1851

    tony1851

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    Hybrid is probably worst of both worlds. If you must split the insulation, it's best to have the vapour barrier on the warm side of the thicker layer.
    PS - the thicker layer must be on top.
     
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