shed flooring

mdf is useless when wet, but not sure if you would actually need and damp proof layer and boards, seal/mastic the shed sides to the base is all I would have done

So is chipboard. But if it's going to be wet, any of them will rot.

Andy

Given the way the base is assembled, I can't guarantee that running sealant around the base would be 100% reliable, so the idea of a liner with boards appeals.

I probably will run sealant around anyway.

Any more thoughts on boards? What's the cheapest per m^2 boarding?

Maybe not a good advertisement, since mine's been damp for the last 5+ years*, but 18mm OSB/Sterling board has survived remarkably well.

• I really *should* do something about it, but the amount of junk I've got stored makes the job tiresome.

None of the above.

I had the same problem with a metal shed & made a slatted floor from treated roofing battens. Keeps stuff off the concrete base, allows it to drain.

Lay 50mm x 50mm floor beams (pressure treated) on the concrete. Tack strips of DPC along the top face of the beams. Screw 18mm OSB down onto them. The DPC will prevent water ingress from the beams and the under-floor space should provide sufficient ventilation to keep things dry enough.

I wouldn't use the a pond liner or any waterproof sheet across the floor area. If water does get in it will be trapped there.

Lay 50mm x 50mm floor beams (pressure treated) on the concrete. Tack strips of DPC along the top face of the beams. Screw 18mm OSB down onto them. The DPC will prevent water ingress from the beams and the under-floor space should provide sufficient ventilation to keep things dry enough.

I wouldn't use the a pond liner or any waterproof sheet across the floor area. If water does get in it will be trapped there.

Don't try and keep it perfectly dry, make sure it's ventilated, i.e. have space between the wooden flooring and the cement.

I've just used some wbp ply to replace a rotting shed floor (soil and sand had spoilt the ventilation), but I'm not sure it's necessarily the best material, just easy to work with.

Yes, definitely, I've posted a similar comment. Air space to let it dry is what's needed.

Which is why a raised wooden floor is ventilated.

I would put down 50mm polystyrene board and then 20mm Chipboard over that.

Thanks for all the tips. In the end, I ignored the suggestions about keeping the underfloor ventilated by raising the floor - the headroom isn't brilliant any way, and losing another 2 or 3 inches didn't appeal. We've put down 2 layers of pond liner pulled up to at provide at least 4cm depth all round and 11mm OSB on top of that. We'll see how things go on over the winter, and if the OSB seems to be getting damp in any way we'll re-consider.

Thanks all.

If I understand that correctly, you have made a shallow pond and put the shed in it. You are now hoping that the rain running down the sides of the shed will not fill the pond up. Even if the liner is pulled up at the edges *inside* the shed, any condensation will be trapped.

Andy

sounds like it :-) not one reply thought the pond liner was a good idea yet the OP went along with that idea , lets ask for help and as long as its what you want to hear its ok if not ignore the answers,OP must be a manager eh :-)

You misunderstood :-) Of course the liner is inside the shed - anything else would be daft!

Any condensation on the walls will run down the walls and will be 'outside' the liner.

There is a fair amount of ventilation from under the eaves so condensation shouldn't be a significant problem

Any condensation on anything stored in the shed will drip onto the floor, and accumulate. It better be dry.

Ask yourself why no-one else ever does this.

Andy