Thanks for your question, as i have a bit of relevant experience here with sealing around the base of a neighbours� shed. looking at the picture above, water drains down the walls of the shed and gets caught up in a small channel that runs around the base of the shed.. What sort of base do i need for my shed? all posh sheds are built with a solid base which acts as the floor inside. this is exterior grade 18mm plywood which we seal on top to prevent staining from any spillages. this plywood is fixed to 38mm (1.5�) thick bearers which are pressure treated to prevent rot, and sit straight onto the prepared base.. When constructing a shed, you need a firm and solid base on which to build on top of. the concrete will need to be made waterproof underneath to stop moisture from rising up. there are two main ways of laying the concrete base..
One of my sheds sits on a base which is almost exactly the same size as the shed. i fitted a wooden 'skirt' around the bottom of the walls so that it overlaps the base and so forms a 'run-off' for rain. i sealed it with 'evostick' flashing tape. the shed is bone dry inside after about 5 years.. Detach the shed from its base and construct a timber floor on raised bearers, dimensions to be a few inches larger than the base measurements of the shed. fix the shed to the surface of the floor with wood screws and mastic seal the inside of the shed base rails. this will allow air flow under the new floor and keep the base area dry.. I've ordered a pre-cut 9' x 13' cedar shed that i will have to assemble. i already have a nice, flat, slightly raised (~ 4-5") concrete pad in place (it was put in by a previous owner)..
