The type of foundation you choose to build your house on will depend on where you live. Your basic choices are a concrete slab, raised floor or crawl space or full basement. Climate and soil conditions will have a lot to do with your choice, although both basements and crawl spaces are built with concrete, either poured solid or blocks. A basement can cost two or three times a crawl space foundation, depending on size and conditions.
You'll Have to Dig
Both crawl spaces and basements require some excavation, at least below the frost line in areas where the ground freezes. That can be three feet or more. Both require building forms and installing reinforcing for poured concrete, the most common type of foundation. Some basements and crawl space perimeter walls are built with concrete blocks but solid concrete is preferred.
Figure Excavation Cost
A basement requires more excavation. The Concrete Network estimates that at $50 an hour, but actual costs vary widely with the type and amount of soil that has to be moved and the size of your house. Excavating in rock will be far more expensive. If your lot slopes, it will cut down the excavation required. In general figure a basement will be about twice as deep as a crawl space.
You Need Forms and Reinforcing
You'll have to have forms built for either crawl space or basement walls. The Concrete Network figures building forms and finishing poured concrete at $1 to $1.50 a square foot plus about 10 cents a square foot for reinforcing bars or other reinforcement. Calculate the square footage of your walls to estimate the cost; a 3-foot high stem wall around the perimeter of the house will have about a third the square footage of a 9-foot basement wall. Stem walls support floor joists just like basement walls do.
Waterproof a Basement
Figure waterproofing expense for a basement, usually with some type of asphalt compound spread on the outside of the walls. Crawl space walls won't need this waterproofing but you'll have to put down a compacted gravel or similar base with some type of moisture barrier. You'll also need proper ventilation to prevent moisture buildup in the crawl space.
Basement Uses More Concrete
You'll need more concrete for basement walls, which the Concrete Network estimated at $75 a cubic yard, and you'll also need a concrete floor. Prices vary widely by region, so you'll have to get a specific price from a concrete supplier in your area. Overall, the Concrete Network figures concrete walls for either crawl space or basement can vary from $1.50 to $4.50 a square foot.
Consider the Value
You need to consider added value in choosing between a basement and crawl space foundation. A basement provides potential living space, which can add value to your home. Think, too, about your area. If all your neighbors have basements, you'll need one, too, to provide comparable value. You may recover the additional expense of a basement with added value and energy savings.
Best for Your Area
Make your final decision on what's most practical in your area. If you're in a coastal zone where sandy, damp soils can lead to wet basements, your choice may be crawl space. If you're in a region where soils freeze in winter so you have to dig below the frost line anyway, a basement may be a cheap extension.