Slab Foundations

The houses, duplexes and apartment buildings use slab foundations. Options for crawl-space foundations are not offered.

Concrete slab foundations cost about the same as crawl-space foundations, but provide superior performance. Slab foundations suppress noise transmission. They also provide thermal mass for stabilizing the temperature of the conditioned area.

Slab foundations are in common use for housing in some areas, but are subject to much prejudice elsewhere. The prejudice is due to problems caused by bad designs when housing slabs were introduced, and to the preference of wood over concrete by builders because most builders started as carpenters.

The most common objections to slab foundations concern cracking, maintainability, climate suitability, and hardness. Slab foundations usually crack, and can become uneven. This problem is solved not by attempting to stop the cracking, but by placing reinforcing mesh in the slab to prevent separation and keep the surface smooth and flat.

It is more difficult to make repairs under a slab floor than in a crawl space. The necessity for repairs can be minimized by placing nothing under the floor except drainpipes and seamless water supply lines, protecting all pipe risers with foam sleeving, and protecting all pipes passing under footings with arches.

Slab foundations can cause problems in some climates. In warm, humid climates, dew can form on slab floors. In cold climates, heat can be lost through the foundation, and water vapor rising through the floor can condense on the inside of exterior walls. These problems can be prevented by placing crushed rock under the floor for insulation, placing a vapor barrier under the floor, and insulating the exterior of the foundation.

The objection that slab foundations are uncomfortably hard is fatuous. A floor is supposed to be hard, and a stiff wooden floor is considered to be superior to a bouncy wooden floor. Slab foundations are common in commercial and industrial buildings, even in elegant shops, hotels, and restaurants.

Leonard Azar, 309 Oxford Street, Brookings, OR 97415, (541) 469-2429, e-mail.