There is no perfect foundation for every situation or every climate. Poured-concrete strips, slabs, block and post-type foundations each have benefits. If plans specify a slab-on-grade foundation, for example, instead of the more traditional full foundation, you will save on excavation and material costs. A slab can also make the home more energy efficient and supply a thermal storage mass for passive solar and radiant heating systems. Without a basement, however, all heating, cooling, pumping and electrical equipment must occupy part of the living space (or an outbuilding). In some regions, a home without a full foundation won’t bring a top resale price.

Foundation walls built with concrete block offer an economical alternative to poured concrete and have many of the same strength and load-bearing characteristics. Held together with mortar, concrete-block walls must rest on a level, solid footing. Reinforcing bars (rebar) are inserted vertically through the blocks’ hollow cores, which are then filled with concrete; this increase resistance to wind and soil shifting. Some of the newest block systems have built-in compartments for foam insulation, making them highly effective insulators.

Many builders prefer to construct traditional strip foundations from poured concrete. They’re strong and familiar to subcontractors, and the process is faster than laying up block.

Although a poured-concrete foundation may look invulnerable, it’s more like a very dense sponge that must be protected with water barriers and proper drainage. Refer to the inspection checklist as workers remove foundation forms and prepare to backfill. Make certain that drainage, termite control, water protection and insulation needs have been addressed. In some regions provisions should be made to dissipate radon gas emitted from subsurface rock.

The dark basement of 20 years ago has evolved. The best custom builders don’t even use the word basement anymore; they call the underground part of a house the lower level. Award-winning builder Robert Rhoads, for example, has turned the traditional American home upside down, expanding the lower level’s size and improving design details.

“Our secret has been to keep the ceilings high—9 or 10 feet,” Rhoads says. “Then we add dramatic impact so that your eyes are directed toward entertainment centers and custom detailing.” Rhoads also makes certain that the stairway leading downstairs feels open, like a stairway in any other part of the house, not a passageway into a cavern.

Any underground space used for living is said to be “conditioned” and will require special insulation and moisture protection. Several systems now offer dramatic improvements over the conventional concrete wall. 

The key to good foundation engineering is to focus on end use. Areas designated as unheated crawl space will require less detailing than conditioned rooms intended daily use. Research shows that un-insulated foundation walls often account for 40 to 50 percent of a home’s total heat loss. Even a simple slab-on-grade foundation needs to be insulated properly.

For example, adding 1 inch of expanded polystyrene (E.P.S.) foam to the exterior of a standard concrete basement wall can raise the wall’s resistance to heat flow from R-2 (about the same as insulated glass) to almost R-7. Adding another inch of foam brings the R-value to R-12, similar to an insulated 2x4 frame wall.

 If your builder uses any type of exterior foam insulation, make sure he covers all above grade material with a rigid fiberglass board or a dramatic facing—such as brick or stone veneer—as quickly as possible to protect the foam from becoming damaged by sunlight.

 During initial meetings with your builder or architect, make clear whether you intend to insulate the slab or foundation wall. Also clarify how you want the above grade portion finished. If you decide to add insulation after the walls have been framed, the extra thickness of insulation and facing may jut out beyond your home’s exterior.

 Radon, Termites and Moisture

In regions where radon gas is common, some building codes now require that builders install a polyethylene barrier beneath the reinforcing wire mesh used in a slab floor. This sheer, which should be at least 8mls thick, not only blocks the naturally occurring radioactive gas from entering the house, but also keep moisture from wicking into the finished slab, where it can cause cracking. An inexpensive plastic pipe set in the slab prior to the pour can save you hundreds of dollars down the road if you detect elevated radon levels in your finished home.

To minimize the impact of termites, some brands of rigid insulation come pre-treated with an environmentally safe deterrent. The best defense, however, may be a good drainage system, since termites need moisture to thrive. By coating the exterior of the foundation wall with a water-proofer, installing proper drainage, and sloping the grade away from the foundation, your builder will ensure that the house is dry and stable for a long time.