Solid wood flooring is 100% hardwood milled from lumber. As a natural material, hardwood reacts to changes in its setting, like moisture and extreme temperatures, which cause solid wood to shrink or expand. All solid hardwood can be sanded and refinished if needed over the years. Solid hardwood is not recommended for installation below ground level or in bathrooms. were originally used for structural purposes, being installed perpendicular to the wooden support beams of a building. Solid wood floors have a thick wear surface and can be sanded and finished many times. Solid wood floors should never be installed floating. The sensitive behavior of wood towards changes in the room’s relative humidity and temperature limits the installation methods to only nailing or gluing down. The wood flooring usually comes unfinished, so sanding and finishing on site is a must. Installing solid wood is then much more complicated and must be done by a professional.