How to fix leaking base of wooden shed on concrete?

cjl1989

Hi everyone, am after some help ASAP! I have a cedar wooden shed that’s on a concrete slab however the slab wasn’t perfectly level and as a result the water pools at the back and seems to be either transferring under the silicone (might be a small cut or crack in it) or via the wet slab outside/the wet timber. Consequently the timber is very wet a lot of the time and a lot of water comes into the shed. I did silicone the inside and as best as I could on the back but there is only 30cm of room (if that) as the back of the shed is up against the boundary fence. Any suggestions as to what I could do? Happy to unbolt the shed from the slab and fix it that way if need be. Pictures attached below. Thank you!

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MitchellMc

Welcome to the Bunnings Workshop community @cjl1989. It's sensational to have you join us, and many thanks for your question about sealing a leaking shed.

Any shed placed on a concrete slab will likely leak under the wall; this is an extremely common issue. To explain further, a shed slab needs to be created specifically for that purpose. The slab must have an elevated portion for the shed's footprint, and then directly outside the walls, it must drop away slightly so that any water that falls on it can't seep under the walls.

You'd need to seal the exterior side of the wall at a minimum. Sealing the interior only stops water from seeping under the wall and coming inside, but it leaves the wall susceptible to soaking up the water, which is the case here. This guide offers a solution to preventing water creep under walls: How to waterproof a shed floor.

Since the slab is sloping towards the shed, I suspect this will be a bit of a battle to overcome. Adding an aluminium angle as per the guide above might provide enough of a water stop to prevent water on the slab from accessing the wall. Installing the angle in such close quarters might prove difficult, though.

Let me mention @Nailbag and @Dave-1 to see if they have any thoughts.

Please let me know if you have any questions.

Mitchell

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MitchellMc

Let me mention @Nailbag and @Dave-1 to see if they have any thoughts.

Please let me know if you have any questions.

Mitchell

Dave-1

Good Morning @cjl1989

I am impressed with your willingness to unbolt the shed! 🙂 I would probarly be thinking the same I must admit as it would give the best chance of solving the issue. Have you just installed it? (As in the past year so you know where all the attachments are?) I think it would be an interesting project to attempt tho more then one person would be needed.

I was thinking of a small awning at the base of the wall next to the fence, maybe a 40mm piece of aluminium to take the water away from the base but still think it would hit the slab and pool back towards the timber base.

Second thought was enlarging the eave of the rear of the shed to keep the water off the wall, maybe even having an eve with a gutter at the top of the fence level so you can access it for maintance. That way you stop the water running down and pooling.

How uneven /sloped is the slab? Does the interior need to be dry? If it dosnt then raising the shed onto some non porous material by even 1cm will stop the seapage along the timbers. Just looking through your photos again, there dosnt seem to me much of a gutter to the roofline? Could you install one to capture the roof water and funnel it away from the slab?

Actually looking forward to seeing how you solve this 🙂 I think it could be an interesting project. If you do go the route of lifting the shed I would screw some timber to a few studs verticaly near the floor and mabe 3cm off the ground. Then use a pry bar to gently lift that section up and slip underneath some 5mm window spacers. Countinue around the shed lifting maybe 5mm at at time and then start again and raise it another 5mm. That way you wont get warping too much (presuming the shed isnt too heavy that is 🙂 )

Dave

Nailbag

Hi @cjl1989 is it feasible to unbolt the shed from the slab, and raise it off the slab with chocks of timber or spare bricks. Then fastening siliconed 25mm square gal tubing all the way around the shed's footprint and then fix it to the tubing. Underlying low points could be packed and siliconed. A big job, but would prevent the timber shed from water damage and solve the water ingress. Shed doo opening ramps are viable to stop the trip hazard on entry/exit.

regards, Nailbag

cjl1989

Hi everyone, your responses were amazing. Managed to follow the guide sent by Mitchell and no leaks whatsoever even with all the pooling that I was getting at the back of the shed. Getting behind the shed was fun... but managed to get it all sorted. Many thanks!

JacobZ

Hi @cjl1989,

That's fantastic to hear.

With the rain we've had in recent times, peace of mind that your shed is watertight is so valuable.

Nice work getting in behind the shed, I imagine it wasn't easy working in such a tight space.

Thank you for sharing your update.

Jacob

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