More Special Sections Hardwood floors can be installed just about anywhere. Concrete slabs that are below ground level, or below grade, are not candidates for solid hardwood flooring. If you have such a slab, I would consider installing an engineered hardwood floor. This material is made by taking different plies, or layers of wood, and gluing them together to make a stable wood product that won't twist or warp when subjected to elevated levels of humidity often found in basements or below-grade slabs.
Wood is a hygroscopic material.
In other words, wood changes its shape in response to changes in relative humidity or the presence of liquid water. As the humidity goes up, or if wood gets wet, it swells. As the wood dries, it shrinks or contracts. This type of movement can cause all sorts of problems with completed wood floors or even wood furniture. For this reason, it is important that the hardwood stays dry and at or near constant humidity levels before, during and after installation.