When you talk about foundations, it's good to build your home on solid rock, not shifting sand. As a matter of fact, that's been great advice for the last 2,000 years.
A slab is the most common type of foundation. It's the easiest to do. All it requires basically, is setting up the boards around the perimeter and then filling the form with concrete. It's also the least expensive. And a slab foundation can be used almost anywhere in the country. The only thing you have to watch out for are those shifting sands.
If you do decide you need to build on shifting soil or an expansive clay soil, you're going to need a different type of slab foundation. A post tension foundation. That's a foundation with cables running in crisscross patterns that we can come back to and tighten up after the concrete has had time to set. You'll have an anchor end that's in the concrete beam, then a cable running inside a plastic sheaf, so the concrete won't corrode the metal. On the other end the cable will go right through the foundation.
There's another variation of a slab foundation called a block and slab, and it really comes in handy when you're building on the side of a hill. The perimeter is built of concrete blocks and then the interior is filled in with stable material like sand or gravel. The top is filled with concrete, forming a slab. And the result is a very strong foundation that will work well if you have a steep grade in any direction.
Everyone likes the idea of a basement because it adds so much square footage to your home. It costs about one third as much to build a basement as it does to build the same size space above ground. And a basement is much less expensive to heat and cool since the temperature of the ground around it will hover at about 68 degrees all-year-round.
If you're building in an area with a lot of solid rock under the ground, excavating a basement may be too expensive. And you remember that expansive soil we talked about? That can sometimes make a basement cost prohibitive, too, since so much extra engineering and construction are going to be required to make it strong enough to withstand the pressures of the shifting earth.
The most important thing to ask your builder for, when you're building a home with a basement, is a tested and proven water sealant on the outside walls. Moisture seeping in from the surrounding earth is the number one problem with basements. And since all concrete will crack somewhere, sometime, the walls need a thick membrane of some expandable material that will stretch with the movement in the concrete and continue to keep the moisture out.
The fifth and last type of foundation is a pier and beam. It's very common, although it's normally more expensive than a slab. The piers can be concrete columns that are placed down into the ground, or concrete blocks that sit on top of pads that are resting on the ground. Wooden beams are set across the top of the piers to provide a base for the sub-flooring. Now the great thing is that you can always come back later and adjust with wedges between the pier and beam if your home ever becomes "unlevel" due to shifting soils.