Breather membrane, dpm, nowt, or NOTA for my shed floor

9 Jul 2008
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United Kingdom
I'm building a shed on a concrete base and am wondering whether to put some membrane beneath the floor.

I suspect the landscaper didn't put a DPM below the concrete.

My shed is actually going to sit on 40x40mm plastic battens. On the battens will go some tonge and groove P5 egger protect chipboard for the floor. The walls will be stud walls lined with OSB on the inside.

Even though no timber is going to be in contact with the concrete, I'd like to be safe so I'm considering draping something over the plastic battens before I put the chipboard down.

I first thought of visqueen type dpm, but then I got concerned that any condensation forming on top of the visqueen would get the underside of the chipboard wet while at the same time cutting down airflow past the chipboard - basically creating exactly the problem I'm trying to avoid. So then I thought perhaps a breather membrane (like under slate roofs) turned upside down?

What do you reckon?
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I would leave out any membrane for the reasons you mention.

Your plastic battens are a damp break between concrete and floor joists.

If you are building the whole shed, use vertical battens to create a cavity behind the cladding
Yep building the whole shed. Going to make the stud walls out of 3x2 treated timber with OSB as the skin on the inside. No skin on the outside of the stud walls. Instead, I'll wrap breather membrane around the outside of the stud walls. Then I'll use vertical battens (like you say) to create an air gap between the breather membrane and the cladding. And then I'm cladding with feather edge fixed horizontally.

I'm plannig to use just some 19x38mm treated tile/roofing battens for the vertical battens behind the cladding. Is that about right?

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