The function of the foundation of a house is to support the weight of the house and to provide a level surface to build on. A foundation for a house can be built from many different things such as stone, brick, concrete block, treated lumber or poured concrete. The three most common conventional types of foundation used today are the poured concrete, concrete block and post-and-pier. There are different foundation construction techniques that you should know before buying or building a house.
There are various foundation types such as the slab-on-grade, monolithic slabs, supported, floating slabs, crawl spaces and basement. The monolithic slabs are often used in places that suffer from sink holes or clay soil. Floating slabs are called that because they are not connected to the foundation and are thus "floating" on the surface of the ground.
Different houses have different foundations. While most houses uses a raised perimeter foundation technique, because it supports both the floors and the wall, other homes are built on a flat concrete slab or rest on a series of concrete piers. It is also not unusual for houses to incorporate a variety of different foundation methods especially if the home has an extra room added on to it. A house that uses a perimeter foundation most likely will have post-and-pier supports beneath the floor beams of a load-bearing wall in the middle section of the house.
Older homes built before the 1960s were mostly pier-and-beam style. Pier-and-beam style homes used the technique of supporting beams every 2 to 3 metres (six to ten feet) by using a concrete pier or wooden posts buried 30 to 120 cm (1 to 4 feet) into the ground. But, the pier-and-beam technique was not without flaws because the wood can rot, the beams can become warped, termites can cause damage and the beams or joists can break.
Concrete slabs came about in the late 40s and helped cut construction costs. There are four main types of slab foundation techniques. Type I slabs use four inches of concrete and use a perimeter beam that is 25 by 15 cm (10 inches by 6 inches).
Type II slabs use four inches of concrete and use a welded wire across the slab along with 40 by 20 cm (16 by 8-inch) perimeter beams.
Type III slabs are 10 cm (4 inches) thick and use perimeter beams along with internal beams every 4.5 metres (15 feet). The beams in a Type III slab are 50 cm (20 inches) deep and 20 cm (8 inches( wide.
Type IV slabs are the best of the four types because they do not cause as many foundation problems as the others do and even work on many unstable soil conditions. The type IV slab is so sturdy because the concrete slab is elevated by concrete beams which are then supported by piers that go at least 6 to 9 metres (20 to 30 feet deep).