Suspended Ground Floors or Something Else

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This topic contains 2 replies, has 3 voices, and was last updated by  Anonymous 8 years, 10 months ago.

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  • #711347


    A bit of a hassle.

    Intended having a suspended ground floor with floorboards as it’s got more give
    and would do less damage to bones, etc in the event of a fall.

    Building codes demand that there must be a minimum 6″ clearance between such
    suspended ground floors (or the insulation under them) and the finished foundation level.
    And there must be sufficient ventilation for the air in this underfloor space — so as
    to avoid the possibility of damp air causing dry-rot in the floorboards/joists.

    Is this regulation any longer approapriate ?
    Dry-rot needs 15% moisture to survive and 20% to expand.
    It is surely possible to have a well-insulated and air-sealed suspended floor.
    And ventilating the underfloor area will inevitably increase heat losses.

    Looking laterally at the issue that brings all this up, would a man be better off
    to just lay a full concrete screed finish (with sub-screed insulation) on the house footing,
    then lay a DPC + spongy intermediate layer upon the concrete and then lay the floorboards on all this ?
    Would this result in a floor just as forgiving as suspended floorboards ?

  • #816752


    don’t you like battens?

  • #816753


    Hi teak,

    The “give” in traditional suspended timber ground floors is vastly overrated.
    In fact if you find there is much “give” in any suspended ground floor, have it inspected unless its over a full basement.

    Normally the timbers bear on joists bearing directly timber grounds on a DPM on tassle [AKA honeycomb sleeper] walls circa 1200mm c/c.
    Tassle walls are walls with a bond which leaves opes of say 1/2 a brick to promote circulation of air in the interstitial space under the floor.
    These bear directly on the slab which should have some sort of outlet/grille from the underfloor area in the wall level with the slab to drain it.
    Under-specified [and older] timber 1st floorsand above can exhibit significant “bounce” but that’s due to minimal specification, a fault, or rot.

    Below are outlined two specifications you might check against your local building code ( is that in America or Canada somewhere? ).
    Both seem to be compliant and I have specified something similar to the one with UFH.
    These are both off-the-cuff this morning so you should check the details.

    Without UFH:

    Fully “Floating” half-timber finish 15-19mm (enough to take three sandings)
    On separating layer
    On absorbent matting
    With UFH:

    Proprietary floating floor
    On clip system
    On lightweight screed incorporating
    Proprietary UFH system with specialist threshold connectors
    On foil backed insulation turned up at room perimeter.
    (there may also be a separating laying in this spec -some suppliers may require it, some may not)
    Slab and Substructures:

    On min 150mm slab sealed with dust-proofing agent
    On min 75mm HD insulation
    On Radon Gas Barrier with Radon Gas Collector Box in Hardcore with evacuation pipe.
    On min 50mm blinding (compacted sand or lean mix)
    On 150mm “whacked” layers of graded hardcore free from soil, impurities and organic material.
    On prepared and suitable bearing ground with all soft areas tamped and filled
    All topsoil and vegetation removed including rootlets
    All projecting rocks removed from exposed bearing stratum

    (Note: in Ireland the Radon Gas Barrier doubles as the DPM although some local authorities prefer 2 no. layers of 500 gauge Visqueen or similar)

    This isn’t a proper specification, just one to set you on your way.
    There is a whole host of stuff regarding the site investigation I haven’t referred to.
    I’m assuming from your posts here you have a clue, but I’m including the disclaimers for those reading who many not be so well informed as you.


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