Types of Hardwood:
Solid hardwood is generally milled from a single piece of wood. Since solid hardwood is a natural product, it reacts to fluctuations in temperature and moisture by expansion and contraction. Therefore, solid wood is only suitable for areas where there is less moisture like on or above ground level—not recommended for basements. Typically, solid hardwood is nailed or stapled to a wood subfloor and is not recommended over concrete subfloors.
Engineered Wood Floors
Engineered wood is constructed from a solid wood top layer attached to a core made of several wood layers (plies) stacked and glued together under heat and pressure. As result, engineered wood flooring is less susceptible to expansion/contraction due to temperature and humidity changes. Because of the enhanced structural stability of engineered wood flooring, it can be installed on any level including basements. Engineered hardwood can be stapled, glued, or floated over concrete or plywood subfloors.