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Internal insulation query

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  • 28-03-2007 9:12am
    #1
    Octopus
    Closed Accounts Posts: 200 ✭✭


    Hi

    I'm going to insulate my dormer style house soon so I searched a couple of topics on the forum, loads of good advice but I was left with a few questions.

    My roof has breathable membrane, do I still need to leave an air gap (50mm) between insulation in rafters and membrane to allow air flow or will the membrane vent any moisture?

    I'll be installing a vapour barrier upstairs at pitched roof and ceiling. Do i need to install the barrier between downstairs and upstairs?

    Just as some background info it's a dormer style house. I'm insulating with rockwool at pitched roof and above ceiling, also between the joists (between downstairs and upstairs, mainly for acoustic properties). Downstairs kitchen and bathroom will have extraction fans.


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    #2
    10-10-20
    Registered Users Posts: 7,163 ✭✭✭10-10-20


    I'm not 100% on this, so I'll reference the Kingspan documents.
    http://www.insulation.kingspan.com/uk/pdf/k7.pdf

    I'm taking the properties of rockwool and Kingspan KoolTherm K7 as being just solely for insulation purposes. Ignore the fact that one is solid and the other is fabric.

    As per page 3, they seem to recommend that the rafters be fully filled when a breathable sarking membrane is installed.
    I would certainly go down that route if possible but it's going to depend on the depth of the rafters. If they are >200mm or so, you've got to ask yourself whether you're just wasting rock-wool by fully filling them.

    In relation to the vapour barrier, if you are referring to placing the barrier between the converted attic space and the rooms below, then no, you don't do that. You want to insulate all of the living space as one. You need to lay it on top and around the attic space. If I've misunderstood you, please let me know.


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    #3
    Octopus
    Closed Accounts Posts: 200 ✭✭Octopus


    thanks 10-10-20

    Makes sense about the 'living space' as one.


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