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General: Cavity depth for NHBC approval?

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    • CommentAuthorchriskemp
    • CommentTimeJul 10th 2012
     
    Can anyone point me in the right direction with regards the depth required of a cavity for NHBC sign off?

    By all accounts (and please correct me if I am wrong) - NHBC still insist on a cavity - even with regards SIPs construction.... I am wondering if a 25mm cavity using battens then external brick slip panels be sufficient?
    • CommentAuthorTimber
    • CommentTimeJul 10th 2012
     
    Yes 25 mm cavity with a 'dry' cladding system should be fine, infact I am fairly sure their technical stanards book gives 25 mm as the acceptable cavity width for things like timber and render on backing board cladding. Brick slip would fall into the render on backing board catagory (for want of a direct reference to it).

    What makes you think that SIPs should be treated any different to any other wood based construction method? If anything, they are more vulnerable to moisture than regular timber frame!
    • CommentAuthorchriskemp
    • CommentTimeJul 10th 2012 edited
     
    ...not if the outer skin is cement particle board ;-)
    And no wooden frame in sight.

    (thanks for the confirmation )
    • CommentAuthorMike George
    • CommentTimeJul 11th 2012 edited
     
    Hi Chris. I beleive the NHBC requirements are based on the relevant BBA or other CEN Certification. For example Partial fill cavity construction requires a clear 50mm cavity where PIR Insulation is used, as this is what is stated a
    in a market leaders BBA.

    So as long as the SIP system is Ceritfied, whatever is specified in the Certificate documentation should be acceptable
    • CommentAuthorRobinB
    • CommentTimeJul 11th 2012 edited
     
    This is a bit of a thick question but how does this square with us fully filling cavaties with polybeads, warmcell or whatever? Are they expected to allow the same airflow as a 25mm clear cavity?
    thanks
    • CommentAuthorchriskemp
    • CommentTimeJul 11th 2012
     
    The system in mind has LABC system approval.
    Usually with a 5mm render direct to the single skin.

    A 25mm "cavity" with an external brick slip panel should be "simples".
  7.  
    Posted By: RobinBThis is a bit of a thick question but how does this square with us fully filling cavaties with polybeads, warmcell or whatever? Are they expected to allow the same airflow as a 25mm clear cavity?
    Cavities in masonry walls can be fully-filled (except in areas of high exposure &/or where there's a risk of the cavity being bridged), because they provide drainage, but not ventilation.

    Cavities in timber frame & timber-faced SIP walls provide drainage & ventilation, so cannot be fully-filled.

    Warmcel is not approved for filling cavities & is normally only used inside the sheathing board of a timber framed wall, i.e. between the studs.

    David
    • CommentAuthorTimber
    • CommentTimeJul 11th 2012
     
    Chris - I would be interested to know which SIP manufarturer is offering a SIP with a CBPB outer skin (is it the Mantle system we talked on here about in the past?)
  9.  
    Posted By: chriskempThe system in mind has LABC system approval.


    That's interesting, have they issued a Guidance note specifying the detail?

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