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Timber frame cavity.

  • 14-09-2008 6:07pm
    #1
    cwboy
    Registered Users, Registered Users 2 Posts: 312 ✭✭


    Blocklayer currently building outside of timber frame.

    His cavity is very narrow in some places and wide in others due to timber frame sitting in a little on the wall plate at one side.
    My question is this: Does the size of the cavity mattter? Why is it 50mm?

    Thanks


Comments

  • #2
    Mellor
    Registered Users, Registered Users 2 Posts: 39,615 ✭✭✭✭Mellor


    It should be 40mm minimum,
    As long as its not under this anywere its ok


  • #3
    cwboy
    Registered Users, Registered Users 2 Posts: 312 ✭✭cwboy


    Thanks for your reply

    What would be the best way to close the cavity in those places where it is wider than the rockwool barriers on the timber frame?


  • #4
    billlove123
    Closed Accounts Posts: 1 ✭billlove123


    The Cavity on a Timber Frame House is 50mm usually.

    The width does matter as the cavity barriers act as a
    fire and smoke 'barrier'. It there was a wider cavity one would
    need to take steps to counter the problem.

    Stainless Steel Brick Ties and Polythene Wrapped Cavity Barriers
    and treated battens on the external windows and doors allow for a
    50mm cavity as Standard.

    Its actually a common problem, to have a 65mm or even 40mm cavity
    due to the inaccuracies in the base - in fairness its easier to make
    a house frame accurate in a factory - but its not so easy get a foundation
    spot on given the weather, conc blocks, mortar types, etc,.

    However both the brick ties and the cavity barrier sleeve allow for this
    in that (a) the ties are short enough so as not to protrude past the block
    on a small cavity. The cavity barriers are 'squashy' so that they can be pressed
    narrower than 65mm thus closing the cavity - this can even close to 40mm but
    be careful with the fresh blockwork.

    All in all, each case will be different but it all depends on the cavity that's built.
    Obviously, if the cavity is an excessive width, say 100mm, then one would have
    to look at perhaps larger cavity barriers (as used in masonry construction 100mm2)
    and larger ties. - Also the roof design may need to be looked at as the soffit width
    needs to be a uniform width all around!

    Is this the first time the block layer has
    come across this issue?

    If you wish I can pm you a pdf of Woodspec Cavity Detail

    I hope this helps.

    Bill


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