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How can I stop rainwater seeping under the shed walls?

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I have a shed (steel frame, metal sides) that has been erected on an existing concrete slab. When it rains water seeps under the walls into the shed. How can I stop this? I have had new gutters installed to keep as much water as possible away from the concrete around the shed but water still comes in. Also the shed is always damp so I think the floor doesn't have any plastic under it. Is putting plastic on the existing floor and relaying concrete over the top so that the inside floor is higher than the ground outside work?


The perimeter of the shed may benefit from the installation of “ag pipes”. Trenches are excavated around the perimeter and a base layer of blue metal is laid. Ag drain pipes connected and laid within; blue metal is laid over the top and the trenches filled. The whole system is connected to your home's existing site drainage system by a plumber. This system will remove any water that comes within the shed's perimeter before it has a chance to enter it. Have you considered laying perimeter concrete paths with falls away from the shed?

It does seem like the concrete slab has not been laid on plastic membrane so it may prove difficult to stop water rising through the slab. A topping layer of concrete laid over the existing on plastic membrane will address this problem but it would have to be at least 50-70 thick with reinforcement mesh.

It may be drastic, but if the shed is not too large, the longer lasting alternative would be to dismantle it, lay a proper concrete slab again then re-fit the shed on it.

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