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Airtightness Layers Questions

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  • 09-09-2010 3:38pm
    #1
    BigGeorge
    Registered Users Posts: 473 ✭✭


    Am looking to airtight a Ppassive house new build by taping, in the walls, the joint of a layer of 9mm OSB inside the service cavity. Believe this is fairly standard & robust detail.

    Its been suggest to double up on airtightness by also including a membrane & taping this also. My questions are:

    - Would this cause any technical difficulties ( other than additional cost) such as condensation etc
    - Which side of the OSB should be membrane be on i.e. on this inside facing the service cavity where it is prone to damage or between the OSB & the stud?

    many thanks


Comments

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    #2
    msft
    Closed Accounts Posts: 11 ✭msft


    9mm OSB is not airtight - that is probably why someone suggested the Airtight membrane.

    18mm OSB with airtight taped joints is an airtight layer - no need for a membrane also. Remember the joints of the boards must be on a solid timber batten all aroudn to ensure the airtightness.
    And also make sure you do the correct spacings and fixings.
    check out <SNIP> and talk to a guy called <SNIP> in there.

    Good Luck


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    #3
    masonry solutions
    Closed Accounts Posts: 10 ✭masonry solutions


    <SNIP> just introduced and airtight block. Combined with epdm (like roofing felt) around window reveals and at wall plate and other areas that will solve your problem along with other methods like where services are brought down internal stud walls fill the holes the plumbers/sparks drill with expanding foam.


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    #4
    BigGeorge
    Registered Users Posts: 473 ✭✭BigGeorge


    Sound advice on the 18mm OSB - much appreciated & makes sense

    What are the correct fixings etc?


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    #5
    msft
    Closed Accounts Posts: 11 ✭msft


    My understanding is:
    Wherever possible, fittings that depend upon face fixing should be selected. Fittings that depend upon the expansion of a component inserted into the board edge should be avoided.
    Fixings should generally be long enough to allow about 20mm penetration into the substrate or have an overall length of about 2.5 times the panel thickness, whichever is the greater. The diameter of the screw fixing to be 0.16 times the thickness of the board - 18mm OSB would be 0.28 diameter, which would be a 3mm diameter screw!
    Parallel core screws should be used because they have greater holding power than conventional tapered wood screws.
    Drill pilot holes for all screw fixing. Typically, the holes should be 85 to 90% of the screw core diameter. Fixings into the board face should not be within 8mm of edges and 25 mm of the corners.
    In environments with typical humidity and temperature conditions, it is recommended that when fixing adjoining square edged panels, that a 3mm gap should be left at all edges of each panel. For all panels that are adjacent to a wall or rigid upstand, a perimeter movement gap of minimum 10mm, or 2mm per metre run, should be allowed.
    For airtightness the joints must be backed with a solid substrate - batten.


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