Every structure on the planet has a foundation. This can be either the ground upon which it is built or a man-made apparatus but whatever the type its sole purpose is to secure the building. It is the foundation that provides the platform to build the home.
Not long ago in this country many foundations were made from flat rock stacked against the dirt walls of a rectangular hole. The earth supported the foundation and the home was built on top of the rock level. Larger rocks formed the base so that the weight of the walls would not cause one of the sides to sink as what happened to the “Leaning Tower of Pisa.†Today, the same ideas are used for building a foundation just the materials and the methods have changed.
In today's building plans the foundation contractor has replaced the big rocks on the bottom of the walls with a system called footers. This is a reinforced concrete base that is wider than the intended wall. Even a slab-on-grade foundation or pilings need a footer system to keep the structure stable. Just think that your own feet spread the weight of your body and if you stand on your tip toes how much pressure there is on that one small part of your body. Another way to look at it is to imagine how a snowshoe lets a person walk on the snow's surface whereas without them he or she would sink well below.
In this part of the world there are three basic types of foundations: slab-on-grade, crawlspace and basement.
Slab-on-Grade
The slab-on-grade foundation is built in places where the ground is not accessible for a basement. This could be in rocky areas or in places where the water table is too high. Footers are still required to brace this type of foundation because it could crack in the middle if not supported. Usually the footer system goes around the outside perimeter of the foundation, or “footprint,†and, in many cases, footers are put in where load-bearing walls will be situated. Then the slab is poured on top of the footprint. In cold climates the footer has to be built below the frost line - around 4 feet deep - to avoid movement.
Before the slab is poured the contractors will take this opportunity to put in water and drain pipe and electrical conduit. In addition, radiant floor heating, either electric or water, would be installed at this time. When the slab has cured the walls will be built using the slab as a platform.
Craw Space
Another type of foundation used where the water table is high, or when there is a lot of clay content of the soil, is a crawl space. Clay soil slows or even resists the draining of water so a basement foundation could be in danger of flooding or water seepage. A crawl space gives the advantages of a basement because pipes and electrical can be run underneath the floor and, unlike a slab, is completely accessible. It also allows for ventilation in hot areas. The walls of the crawl space sit on the footer which, in cold climates, must be below the frost line.
Basement
Having more headroom than a crawlspace a basement can give added living space to a home. In areas where the water table is high people still build basements but put in a sum pump system below the floor. This will take away pooling water in times heavy moisture content in the soil, like the spring and fall.
Foundation Materials
Concrete: The favorite for all foundations is steel-reinforced, concrete. These are built by putting wooden forms of the footer and by tying the system to vertical rebar coming out of the footer the foundation becomes immovable. The only drawback with concrete is that the curing process will create pressure cracks so the exterior has to be waterproofed before backfilling takes place. A proper drainage system should be installed down at the footer to lead water away.
Concrete Blocks: Also called Concrete Masonry Units, or CMU, these are hollow concrete blocks that are stacked together like large bricks. The hollowed center usually features vertical rebar for support and sometimes loose insulation is used to fill these voids as a sound-deadening material. CMU's should be waterproofed as moisture can find its way in to the basement or crawlspace in the mortar joints.
Insulated Concrete Forms: ICF's are foam blocks that stack together to form a wall and then are filled with concrete. Like the other materials vertical steel-reinforcement bars are used to tie the system to the footer and horizontal ones to strengthen the walls. When the concrete has cured, the foam on both sides gives a great insulation factor as well as a sound-deadening factor. ICF's can go right from the footer to the roofline and form the walls as well as the foundation.
Pressure-Treated Wood: In areas where the ground is dry and sandy a foundation can be built using 8†x 8†vertical posts and plywood sheathing, all pressure-treated. This received a waterproofing sheathing as well. With this type of basement is dryer than the concrete ones because the moisture does not accumulate like it does in a concrete basement.
Posted by: TrustedPros