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Air Tightness and MHRV in Dormer House

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  • 23-11-2014 1:29pm
    #1
    Yes Boss
    Registered Users Posts: 424 ✭✭


    Hi All - I am building a dormer style house and am looking for some guidance on the following:

    In the sloping section of the roof I am installing 100mm Kooltherm between the rafters and 72.5mm insulated plaster slab. The question is - Do I need to install an air tightness layer or does the insulated slab perform that function? Do I need a service cavity in the sloping roof and is that inside the insulation?

    How do I address air tightness in the section of ceiling that is not used as floor area at first floor?

    Also, would any like to recommend a Heat Recovery Ventilation System? I would like a reasonable quality system that is easy to maintain. Also, will this system manage the moist air in bathrooms, kitchens etc?

    Thanks in advance for any advice.


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    #2
    Yes Boss
    Registered Users Posts: 424 ✭✭Yes Boss


    Also - can anyone recommend a wall tie for a 150mm cavity with partial fill insulation?


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    #3
    BryanF
    Moderators, Home & Garden Moderators Posts: 10,140 Mod ✭✭✭✭BryanF


    You need an air-tightness membrane/vapour barrier

    A Service cavity is a good idea. If you don't create the cavity inside the air-tightness layer, you need to provide for suitably sealed penetrations.

    Air-tightness details are designed and considered before 1st floor/ceiling goes in.

    MVHR will take moist air out of the wet areas

    I'm sure you can google 'wall tie'?

    May I ask
    1.what stage are you at?
    2. Have you appointed a design certifier?
    3. And are they preparing your air-tightness details?


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    #4
    Yes Boss
    Registered Users Posts: 424 ✭✭Yes Boss


    BryanF wrote: »
    You need an air-tightness membrane/vapour barrier

    A Service cavity is a good idea. If you don't create the cavity inside the air-tightness layer, you need to provide for suitably sealed penetrations.

    Air-tightness details are designed and considered before 1st floor/ceiling goes in.

    MVHR will take moist air out of the wet areas

    I'm sure you can google 'wall tie'?

    May I ask
    1.what stage are you at?
    2. Have you appointed a design certifier?
    3. And are they preparing your air-tightness details?

    Bryan - Thanks for the response.

    Do the air tightness/vapour layer go between the rafter and the insulated plaster slab?

    Drawings are being prepared for tender.
    Yes - a Design Certifier has been appointed.

    I would just like to know the best way of approaching air tightness in the dormer roof as I know it can be a difficult area.


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