DPC under a shed?

[damouse]

Hi all

I have a new and empty 10x8 shed - built and sitting on a concrete slab as of last weekend. After yesterdays deluge of rain I'm kicking myself for not putting some damp proofing down prior to building.

I'm considering running some 100mm DPC (the roll type) down under the bearers but I have to get the shed lifted ... and then lay the membrane down in such a way that it won't shift when I move the shed into the right position.

The shed is tanalised and I am planning to weather protect it this weekend with osmo oil / stain so am I going overboard in trying to run a DPC under the bearers?

What do you think guys? also - any tips on how best to lift it up - I'm thinking I may be able to get a car jack below along with bricks to prop up.

Cheers for any advice!

Pic below showing water penetration (though it looks like this is not damp on the inside as far as I could tell)

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• damouse
• 15 May 2015
• 1

 

[stem]

First of all that watermark will more likely be as a result of the rain water dripping off the roof and either hitting the bottom of the shed on the way down, or splashing up on to it from the ground. This will be why the inside of the shed is unaffected and why the watermark extends up the door which isn't actually part of the structure in contact with the ground. A gutter and downpipe will prevent this happening.

It would also appear that the shed is pretty much the same size as the slab, so the shed should pretty much shelter the slab from direct rainfall under normal weather conditions.

If you put a damp-proof membrane under the timbers, it will be too thin to raise them out of any puddles that may form, so any water that does run under the shed will sit on top of the membrane and the only way it can go is up and into the shed, so it may make the situation worse. The only way to avoid it completely would be to lift the shed on concrete blocks or tiles so that the base timbers were high enough to be clear of any sitting water.

99% of sheds I have seen are sited exactly as yours is, including my own which is now 16 years old if the base timbers are tanalised, you should have nothing to worry about.

 

[Bosswhite]

Mini Guttering down pipe and Water Barrel should solve the problem, ( and be useful for the garden)

so long as the barrel does not overflow,

 

[damouse]

Many thanks guys

 

[mattylad]

I hope that before you put it up - you coated it all in preservative?

The bottom is usually the first bit to rot on all sheds, roll it over and give it several coats - it will extend it's life.
(The suppliers may say that they are already coated - but its hogwash - needs doing again)

WHile it's empty & without glass - a car jack & some planks will enable you to lift corners (in fact just a wump of wood may do) and then brick it up.

But I'd roll it and wrap the DPC around the bottom and staple it.

 

[damouse]

I'm very much wise after the event


Seems like getting some mini guttering is a sensible route - that may end up being all I need to ensure water stays off the concrete slab / prevents splash back

However - the slab base is much larger than the shed - I've just not managed to put it into the final position hence it looks like it is overhanging.

So I may yet try to get a dpc roll lined down below the bearers ... but stapling these up so they don't collect water will be very tricky as I don't think I can raise the shed high enough for me to crawl under and do it that way - unless we are talking about laying dpc just on the bearers that are on the outside?

I'm wondering now if I should just pick up some cheapo flat concrete slabs from B&Q or somewhere and have the shed timber bearers sitting on these ... That in itself will be interesting as I'll need to somehow position the ones that sit in the middle of the shed itself! ... How many slabs would you recommend in this scenario - can I put them in a checkerboard fashion or would I need enough to cover the whole of the base?

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• damouse
• 18 May 2015
• 1

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• damouse
• 18 May 2015
• 1

 

[foxhole]

I raised my 10 x 8 on 4 pallets. keeps it high and dry and simple enough to replace when they eventually rot.
Use leverage to raise each corner, a long timber over a fulcrum [another timber] will allow you to raise it effortlessly.
If you use slabs you can push them under using a length of timber.

 

[joe-90]

I had a shed sitting on concrete paving for 15 years - not a problem re rot. Wasn't even tanalised.