Basements are subject to damage from ground moisture, so choosing the best basement subflooring is vital to creating a livable space with minimal problems. The best choice for basement subflooring is concrete, since it is both strong and water-resistant, and it is a great choice because it provides a flat, smooth surface for tiling or other types of flooring that might be installed on top of it. If the builder decides he or she wants a raised floor — that is, a floor that is raised off the concrete foundation so plumbing or wiring can be run underneath the floor — then a wooden subfloor must be built.
Wooden subfloors work well as basement subflooring if the wood is properly treated. Even if the wood is treated, after several years subfloor boards may need to be replaced due to rot or cracking. The best combination is to build treated wood basement subflooring over a concrete slab. This provides a layer of water resistance between the wood and the bare ground. The concrete slab should also be treated for water resistance or waterproofness, though concrete alone can still provide a high level of water resistance.
If the basement is bare dirt, a concrete slab can be poured and used as basement subflooring. It should be poured on top of a leveled layer of cinders or crushed stone to provide yet another level of water resistance as well as a porous surface to which the concrete can adhere. Once the concrete has set, another layer of waterproof material can be sprayed or painted onto the concrete, or rolls of waterproof rubberized membrane can be applied to the concrete. A concrete subfloor is a great option if the basement will be finished with stone, tile, or other flat materials that will not have plumbing or wiring running beneath them.
Another option for basement subflooring is a series of interlocking plastic panels that are dimpled on the bottom. This creates a gap between a concrete foundation and the flooring itself. Moisture will stay within the gaps of the dimples or in the concrete itself rather than escaping upward into the floor or the finished room. Dimpled plastic panels are easier to install than other types of subflooring, but they can be cost-prohibitive and they come with their own sets of problems. If flooding occurs, the panels need to be torn up to be dried or drained, which means any flooring installed on top of this type of subflooring will also have to be torn up.