Solid wood boards are made from a single piece of timber. They can either be glued to a suitable concrete sub floor or nailed to a suitable wood sub floor. Solid wood flooring is susceptible to fluctuations in humidity and is therefore unsuitable for certain installations such as basements, over underfloor heating, conservatories and bathrooms. On the plus side, a solid wood floor can be refinished many times and is generally cheaper than engineered floors.