Q: I have a fun project and I need an expert opinion. I have a 13-by-20-foot outbuilding I use as a garden shed and "man cave." It has a concrete floor that was poured in three sections, so there are seams and some parts are higher than others.

The back of the building faces upslope to a neighbor’s yard. After a good rain, a little water seeps in. Last year, I installed drain rock and perforated pipe to route the water away. This has helped, but the building is by no means waterproof.

This summer, I want to put a wood floor over the concrete. My plan is to put shims on the concrete to level it, then add new flooring on top. The new wood floor would also cover any moisture that finds its way in during the rainy season.

I know this sounds cheesy but I want to do this on the cheap. After all, it’s just a garden shed. For the top flooring, I was considering 2-by-6 planks but wonder if I might get by with 1-by-6s instead. Again, I’m not looking for high art, just clean and functional.

Is this reasonable? I’d appreciate any suggestions.

A: Your plan is more than reasonable: It’s good, but with a little modification. Remember that water is the enemy. Your friends are air flow and water-resistant materials. Good ventilation and using the right stuff will give you a useful and comfortable man cave.

Your idea of using shimmed floor joists to level the floor is right on. But there’s a little prep to do before setting the joists and laying the floor. We recommend 2-by-6 pressure-treated boards laid face up for the joists. Joists should be laid 19 inches on center. This will give a minimum 1 1/2 inches space between the bottom of the flooring and the concrete slab, and about 14 inches between joists.

Because some water is seeping into the shed, your first step is to make the slab water resistant. Caulk the seams between the slabs with caulk made for concrete available at hardware stores and home centers. Then treat the slabs with a water-repellent finish. Concrete sealer or concrete paint will do the job. Do a couple of coats.

Your next job is to provide some ventilation. Start by laying out the floor joists perpendicular from the back of the building, but don’t set them. Mark each joist location with a pencil. Then drill four 1-inch ventilation holes in each bay between each floor joist at the rear and the front wall.

Clean out the debris from the holes and then nail wire mesh over the holes. Use heavy-duty staples or roofing nails to secure the mesh. This will keep small critters from nesting under the shed.

Now, set the floor joists. Use 2-by-6 pressure-treated wood with the 5 1/2-inch side resting on the concrete. Use construction adhesive and concrete nails set with a .22-caliber concrete nail gun. Level the joist with cedar shims treated with a water-resistant sealer. When the joists are set, caulk the edges to prevent water from seeping under them.

Finally, nail the flooring in place. While 1-by-6 planking would probably work out OK, we’d like something beefier. Rather than using decking, we suggest you use 3/4-inch tongue-and-groove plywood, commonly used for subfloors in new construction. The floor will be stout, to say the least.

This will be cheaper and stronger than single boards. If you don’t like the look, paint the floor. Or, if this truly is a man cave, carpet it. Heck, we’d get out the 4-inch hole bit and sink a hole in the corner so we could practice our putting on rainy days.

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