Definition Of House Foundations
The house foundations is the system on which the home sits. Sometimes the house foundation rests upon the footings and supports the floor system - as with conventional foundation walls and piers.
Sometimes the home foundation is also the footing - as with a home built on piles driven into the ground. Sometimes the footing, the foundation, and the floor system are one - as with the monolithic slab.
Types of Foundations
Which system you choose will depend on several factors. Some people believe a foundation system with a crawl space is better. They prefer the "live" feel of a wood floor system and believe it is not as cold as a slab.
The fact is, a properly insulated slab can be just as warm as a wood floor. If you have a basement, you'll have a slab at the basement level and a "conventional" (framed wood) system at the other floor(s).
If you have a crawl space, you'll have to provide an access door of at least 18"x24". You must also provide ventilation at a rate of one square foot of opening for each 150 square feet of crawl space. This is usually accomplished with rectangular foundation vents. One vent has to be within three feet of each corner.
Many foundation systems consist of a masonry (brick or concrete block) perimeter wall sitting on a concrete footing.
Inside the perimeter wall there may also be a number of piers, columns, or posts spaced within the area surrounded by the wall or immediately adjacent to and built into the wall itself.
The interior piers sit on their own individual footing pads, and are there to support girders or beams, which in turn support the floor joists.
The thickness of the wall and the sizing of the columns and piers depends on the materials used and the loads being supported. Placement (spacing) of the piers depends on the size of the beams sitting on them (larger beams will span greater distances).
Your architect will be comfortable in specifying the proper size and spacing for 275500each of these elements. If you are unsure, check your building code and with your local building official.
Poured concrete foundation walls are popular in many areas of the country, and are almost always used where there is to be a basement.
Wood or metal forms are set on the footings, reinforcing steel bars (rebar) are added to strenghten the wall, and concrete is poured into the forms. Before the concrete is "set," anchor bolts are pushed into the concrete along the perimeter of the home.
They are used to secure the exterior walls - a very good idea in areas where strong winds are a possibility.
Of course, as with everything else in home building, there are lots of local variations that you may run into with foundation design.
As with footings, foundations can also be "stepped" down a hill.
Caisons For active soils
If your lot has expansive or active soils, you may be faced with installing a specially designed house foundation system which uses "caisons." This foundation system is complicated enough to deserve its own page! Click here.
If you are interested in a Wood Panel Foundation system mentioned above, check out the official web site here. Thousands of homes have been built using this system. The advantages are the ability to get the house foundation in during bad weather, the elimination of one trade (masons or concrete foundation sub), and it is fast.
Pressure Treated Wood Foundation System
Pile house foundations are really a general class of foundations of which the caisson foundations described above and here are a member. Most of us are familar with pile foundations as seen in beach houses. Here's a good definition from Answers.com.
Piles are typically used where the availabel soils are unable to support the necessary loads with the use of more traditional spread footings and their supported masonry or concrete foundation walls.
A pile driven home foundation should be designed and its installation be supervised be a comptent engineer. Here's a great site on the actual design of piles for a foundation.
Don't confuse piles and piers!
Piles are driven into the ground to support the load on underlying bedrock or by the actual friction between the piles and the soil they are driven into. See the beach house above.
Piers are supported at ground level by their own footing - usually a concrete pad. They are used simply to elevate the home above the ground.
Other house foundation elements
You will find other things going on with foundations - particularly when you are dealing with basement foundation walls. The following photograps will illustrate some of the more common.