Damp proof for timber frame on concrete?

Discussion in 'Builders' Talk' started by mja1, Dec 30, 2019.

  1. mja1

    mja1 New Member

    I am building a small timber outbuilding (to be a potting shed) on a concrete base.I have laid out the two-by-four timber frame (which will eventually all be covered in cladding) but not yet attached it to the concrete floor.

    My question is: should I add some form of damp proofing between the timber frame and the floor? If so, what would be best on a shoestring budget?

    Many thanks
  2. rogerk101

    rogerk101 Screwfix Select

    If it were mine, I'd do the following ...
    • Make up a nice workable mix of 4:1 mortar. (I'd add a cap full of plasticiser to make the mortar even more workable, but that's probably just because I already have a 5 litre bottle of it.)
    • Lay a shallow bed of the mortar the width of the 2x4s that you're about to set onto the concrete base. This is to raise the timber slightly above the concrete base just in case the base accumulates water through some sort of water ingress.
    • Lay a strip of DPC on top of the mortar to create a barrier to prevent any damp rising through from the concrete up into the wood.
    • Bed the 2x4s onto the DPC and compressing the fresh mortar until each of the 2x4s is level and they're all at the same height.
    • You could fix the timber into the concrete at this stage using appropriate fixings or you could wait until the mortar has set and then do the fixing then. The latter would be my choice. (You do need the fixings otherwise the shed risks moving off its perch or even being blown over in high winds.)
    KIAB likes this.
  3. Hello...

    found this thread as having bit of a saga trying to put a gym in my back garden.

    ive finally had the concerete pad in, with a DPM.

    And ive got the timber (45 4x2s pressure treated decking joists) and 19mm cladding sat in my garden waiting to be built.

    The plan is to not have a wood floor, and just build a shell around the concrete so have the concrete floor as my base. then ill just seal / dust proof it and put rubber mats over it.

    But, i didnt even think about damp rising up from the concrete into the timber sat ontop of it.

    Is this really a simple case of laying the timber on a piece of DPM the length and width of 4x2 frame plates?

    Without going down the mortar route?

    Thanks, any advice is greatly appreciated as this has been a real task getting together!

    Thinking on roof too, do people on here rate EPDM roofs, or is felt or corrugated stuff better (and obvs alot cheaper). Cheers, B

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