Making Shed water proof.

by James

Hello there. I am quite confident about how to make a strong and stable shed but not about making it watertight. I'm just not sure about how to waterproof the four exterior walls, corners and also the bottom strip of cladding.

I have viewed some garden sheds and they seem to be fully clad on one wall and the adjacent walls are almost fully clad except they have a thin wooden strip running their height at their edges, the strip which makes up the four corners of the shed and the strip which touches both the cladding from the fully clad wall and the adjacent wall which is fully clad minus the inch or so which is left to house the strip. I would love to go ahead and start this right now, but I can't see how this strip covering the joints of the four walls will keep the water out and feel there must be something inside the wall to wall joining that I'm missing.

Also, in regards to the bottom most strip of wall cladding, which passes the join between wall and floor, is there any need for a waterproof barrier? So is there any need for a barrier between the bottom-most piece of wall cladding and the framing of the shed?

Hope I have made it clear enough.

Thanks for your time, James.

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Waterproofing your shed
by: David

Waterproofing is indeed a difficult task. You must accept that there will be some water ingress but plan to minimize this.

Generally keep a good circulation of air around the structure. If you have space, keep 2' to 3' around the sides, also keep the floor (if not concrete)off the finished grade (earth / soil / hardcore).

Circulation of air around and underneath will assist in drying off any moisture getting on the surface of your shed.

In respect of elevating the shed floor out of harm's way my preferred method is to use two layers of 100mm (4") concrete blocks to sit the floor's sub-structure onto. Generally four stacks per 12' length and 2 stacks per 8' width are adequate.

I prevent wicking-up by using DPC or old/scrap roofing shingles between the concrete and the mud sill of my sub floor.
Joseph Truini's book on shed building in the "Pro" series has further details on methods of building foundations.

Also I do tend to sheath the walls (beyond the floor level and the rim joists)and roof structure with OSB 3 / WBP plywood, thereafter I will attach a vapour barrier fabric before cladding with lap, shiplap or TGV.

This does push the cost higher of course but the long term benefits outweigh the initial costs in respect of longevity / stuctural integrity and avoiding that nasty musty smell of damp.

As the rain is the most obvious source of water, don't skimp on the roof covering. My advice is to look to use at least two layer systems and if the project budget allows a 3 layer commercial system.
Many of the roofing materials manufacturers have great advice on their websites.

Finally I always advocate proper ventilation through the soffits and, where practical, fit my own timber louvred ventilators in at least one of the side / end panels. the shed will get wet but good ventilation will help dry it out pretty thoroughly.

All the best - David

waterproofing your shed
by: John Shank

Hi James,

The corner strips you are referring to will not totally waterproof your shed corners. Whenever I build sheds and use these, I run several lines of caulk under the inside surface, and also after they are attached to the shed, I will then caulk the edges all over so no water penetration occurs.

This is not a foolproof solution, however, it will definitely slow down the water penetration and protect your shed for a longer period of time.

As for the siding, usually the bottom goes down past the floor decking on the outside and therefore no water can run underneath the siding onto the shed floor.

You can apply 'sill paper' to the underside of your shed walls bottom plate also and this will add extra protection from moisture wicking up into your shed wall should any happen to find its way to the bottom of your shed wall. I also build my shed walls using treated lumber for the bottom plate and also use treated lumber for all the floor pieces for a longer lasting floor.

Hope this helps you.


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