Ask FRED: How Do I Install Wood Floor Below Grade?
Installing a wood floor below grade can be done with the right preparation. First you must tape a one by one square foot piece of 6mm plastic to the concrete slab in a few locations and wait one week to see if water appears inside the plastic. This will let you know if moisture is coming through the slab, if yes you will need to address this problem before continuing. To address this, it could mean a French drain with a sump pump, or just seal the concrete slab with the proper floor sealer, all depending on the amount of water found under the plastic. Now that you have the answer to this question you can choose the product that fits your situation.
LVT is a luxury vinyl tile that is designed to be used in moisture prone areas. In this scenario, this product can be installed over a moisture barrier and installed as a “floating Floor”. If no moisture barrier is needed, this product can be glued directly to the concrete.
An engineer floor is a wooden layered floor similar to plywood with the top layer bringing a veneer of the finished floor and can’t be refinished. This can be installed over a moisture barrier if it is a click lock product, or over a sleeper system if it is nailed down.
Sleeper install method is where the concrete is covered with a layer of taped down 6mm plastic with pressure treated 2×4 placed flat on the floor and secured to the concrete with screws. Then a layer of ¾ inch plywood. Now you can install a engineer nailed down or standard ¾ inch wood floor. It is always recommended that you consult with an expert prior to attempting this type of installation. Considering the necessary precautions will save time and money and ensure that the product will endure.