Solid hardwood floors are made of planks milled from a single piece of timber. Solid hardwood floors were originally used for structural purposes, being installed perpendicular to the wooden support beams of a building known as joists or bearers. With the increased use of concrete as a subfloor in some parts of the world, engineered wood flooring has gained some popularity. However, solid wood floors are still common and popular. Solid wood floors have a thicker wear surface and can be sanded and finished more times than an engineered wood floor. It is not uncommon for homes in New England, Eastern Canada, USA, and Europe to have the original solid wood floor still in use today.
———————————Reprinted from Wikipedia