Shoring is a type of temporary prop or support used in the repair or original construction of structures and excavations. Temporary support, for example, may be necessary to ease the weight on a masonry wall while it is repaired or strengthened. The word comes from the French word équiper, which means "to equip." In construction, shoring consists of any of various devices used to provide support for the sides of a hole or excavation before they are filled in. The most common types of shoring include: timber framing, plastic sheeting, and metal cages. Timber framing is the most common form of shoring. It usually includes two sets of lumber spaced about 18 inches apart. The function of this framing is to give added strength to weak areas of a structure, such as around windows and doors, and in floors and ceilings. The top set of boards is called a header. It is designed to carry the weight of the roof or ceiling it forms, so that heavier elements of the building aren't forced into more vulnerable lower parts of the structure. The bottom set of boards is called a footer. It acts as a foundation for the house, providing stability when the ground it rests on slopes or moves due to frost heaves or other causes.