AS EVERYONE knows, the foundation is important for holding the house up.  Everything rests on the foundation, both literally and figuratively.  If your foundation isn't built properly, it will affect everything on the rest of the house.  There are several types of foundations, some common, some not so common.  The chart at the bottom compares the cost of these foundations based on a 32'x40' house footprint with a standard 8" stem wall over a 16"x8" thick stemwall for a two story.  Footings and beams are placed as smartly as possible and any joists are 2x12.  Any common items for all types are not considered in the cost.  (visqueen, holddowns, drain tile, etc.)

Slab: 

One of the most common types of foundations is the slab.  The slab is simply a flat piece of concrete poured on to the ground.  The edges are thickened or rolled under to provide bearing for the walls.  Slab foundations are not exempt from thickened footings in the middle to support point loads.  The benefits of the slab foundation are one pour and you're done, not only with the foundation but the floor as well.  As soon as the concrete has cured, you can start building your walls.  The drawbacks are that straight concrete is a cold floor and it loves to destroy your fine china and crystal that slips out of your hands.

Post and Beam:

The post and beam (or post and pier) foundation utilizes 4x8 beams over a regular spacing of footings (generally in a 4'x8' grid).  The exterior foundation is a standard stem wall and footing.  The benefits of the post and beam foundation are the low profile, especially where there are height restrictions.  No joists are required.  The drawback to the post and beam is the extra cost of all the footings (though possibly offset by not needing joists) and the difficulty of using it on complex houses.  Complex houses consist of either several point loads or significant jogs in the foundation.

Joisted:

The joisted foundation is sometimes referred to as crawl space.  This is a misnomer as several other types of foundations are 'crawl space' as well.  The joisted foundation places joists at regular intervals over beams which are then on top of footings.  The difference from the post and beam foundation is notably much fewer beams and footings.  The benefits of joists is raising the house off the ground for a more commanding look, and far easier to implement for complex houses.  The drawbacks to joisted foundations are possible extra material costs for the joists, though the thinner subflooring and lack of interior footings could offset this.  In most cases, istockhouseplans is preferential to the joisted foundation.

The Strip Footing foundation is similar to the Joisted, with one difference.  Instead of beam lines supporting the joists, stemwalls and footings are used.  Sometimes the stemwall is replaced by a cripple wall on the footing.  The benefits are found in stability of the foundation, especially for sloped or seismic reasons, but the cost of the extra concrete is more than the savings of the beams. 

Post and joist:

A very uncommon hybrid system is the post and joist.  This foundation type has regular footings as the post and beam (generally 32"x8-10') with joists instead of beams running over top of the columns every 32".  We know very little about the benefits and drawbacks to this system.  We imagine it to be relatively cheaper to build, but easier to screw up.

Stilted:

One of our favorite stilt houses has nine footings at the corners and center of the house.  From these footings rise steel beams to connect to 3 or 4 other points of the house.  The whole mess looks like some gigantic robotic spider built a web and caught a house in it.  This particular design created a large flat platform to build the house on where there was otherwise an unstable hillside.  Just don't drop down through any crawlspace access...

Levitating:

A nice solid platform with powerful turbines underneath should be able to elevate your house to new heights.


 

Foundation Type Cost Comparison


Slab Cost P&Beam Cost 16" o.c. Joist Cost 16" o.c. Strip Cost
Footing 23.8 yds $2,380 4.75 yds $475 4.75 yds $475 4.75 yds $475
Stemwall 16 yds gravel $400 4.75 yds $475 4.75 yds $475 4.75 yds $475
Int. Ftgs. x x 1.3 yds $130 1.2 yds $120 4 yds $400
Rebar x x 288 ft $105 288 ft $105 416 ft $150
Columns x x 2-4x4x12 $25 4x4x8 $10 x x
Beams x x 18-4x8x16 $660 6-4x10x12 $205 x x
Joists x x x x 50-2x12x12
29-2x12x16
$1,050 50-2x12x12
29-2x12x16
$1,050
Subfloor x x 2x6 T&G $1,175 40- 1/2" pwd $900 40- 1/2" pwd $900
Totals
$2,780
$3,045
$3,340
$3,450

All prices are approximate as of July, 2007, do not include labor, and have been rounded up to the next $5 increment. Prices may be different in your area.