A crawl space is a unoccupied, unfinished, often narrow space in an apartment building, sometimes between the upper floor and the ground level. The word “crawl” is derived from the French “celoc” meaning heap or mass. The term is often used in association with the practice of utilising the basement as a living space, with the kitchen being the most common use.
The term is sometimes also used when describing the concrete slab on which the building’s foundations are poured. A crawl space may also be defined by the height of the slab foundation, i.e. if it is above ground the term may apply, otherwise it will be necessary to specify in the building plans. The term is also frequently used when describing unheated crawl spaces, i.e. those below the earth’s surface.
The main purpose of a crawl space ventilation opening is to allow excess moisture and gases to escape into the atmosphere. This is usually achieved by using a vent hood, which can be installed directly over the opening or via a system of ducts or vents. Although vents can be installed directly above the opening, this is not usually recommended because the pipes often contain moisture. Instead, a trenching system is often used to channel the ventilation into the walls. If there are no ventilation ducts or vents to the outside, the soil around the foundation may be excavated to expose a flue, or to install a vent pipe for external ventilation. If no drainage is available then root access to a condensation damper may be required.
A typical component of a crawl space are earth floors and exposed ductwork and plumbing. Earth floors provide a natural heat source that can be maintained by heating and damp proofing the floor. In addition to heating and cooling, earth floors should also be sealed to keep water away from foundation walls. Usually, the floor drain and slab on top of the foundation will slope towards the house foundations will be buried in the soil.
In general, a slab on the exterior of the house provides the foundation on which the house rests, and has a concrete floor that is waterproof. This slab should be sloped towards the house to facilitate soil excavation to install foundation walls and to channel excess moisture away from the house. On the interior of the crawl space, the concrete slab is typically cracked to provide access to the earth for foundation walls and to channel excess moisture away from the house. Cement sealant is typically used as a sealant between the slab and the wall and between the slab and the floor drain. The interior of the crawl space can be made with plywood sheeting or with poured concrete slabs to match the exterior concrete floor.
Wood rot and termites are potential problems that have been associated with unventilated crawl spaces. Termites will chew through wood, entering the crawl space through a termite tunnel. Wood rot will cause rotting and expansion of the interior of the crawl space, which can allow condensation and moisture to build up. Wood rot will also cause the foundation of the crawl space to settle unevenly, compromising the structural integrity of the house. If you discover any of these conditions, you should contact a licensed home inspector who will assess the condition of your foundation and recommend an appropriate repair plan.