Monday, April 12, 2010

How House Foundation is Built - Difference Between Crawl Space and Slab

Building a house starts from its foundation (the most important part). The weight of the house are supported by the footers and foundations, and they are usually made from concrete or masonry. After this is completed, the ground floor can be built from wood or concrete. And when the floor is completed then framing (the process of using wood or metal beams) begins.

Houses today are generally built on a foundation that is either a slab, a crawl space, or a basement.  Basements are more expensive to build, but many people are willing to pay for it since land costs are very high because basements allow for the more living space. Depending where and when a house was built, its foundation can be made of brick, stone, preservative-treated lumber, concrete block, or poured concrete. The most common foundation's material today is concrete.

house foundation construction
When building the foundation, rocks, trees and debris have to be removed first from the site. With the help of a backhoe and/or a bulldozer, they dig the foundation to the depth presented in the building plans. The depth of the foundation varies with the size of your building structure. Large construction buildings require a deep foundation whereas medium and small homes can be built upon shallow foundations.

Usually they will also contact the plumber, electrician and heating company to ask them if there is anything they need to install in the foundation before the concrete is being poured.

The bottom part of a foundation is called a footer (or footing). It is usually wider than the foundation wall, footer is located about 12 inches below the frost line (this is the average depth at which soil freezes year after year).

For a crawl space, they will dig a set of trenches and holes before pouring concretes into them so that the interface between the ground and the foundation wall can be created. The width of these concrete beams are controlled by the compressibility of the soil. The floor of our home is built up on foundation piers. It gets our house up off the ground, this type of foundation is very useful in damp or termite-prone areas.

A crawl space allows access aruond the lower level of our home. We can crawl into the access foor below our home to handle most of our maintenance issues. Many times the electrical, HVAC ductwork and plumbing will be housed here also. With this type of foundation, moisture is one of the biggest drawbacks, it can lead to potential termite damage, rotten floor joists, and/or mold.

concrete slab foundation
The slab is probably the easiest and most affordable foundation to build. A slab sits directly on top of the land. A slab is a flat concrete pad poured directly on the ground. Once it's poured, wall construction can begin the following day. There is no space between the lower level of our home and the earth. With this type of foundation, most of our “rough-in” plumbing is non-accessible from below and we must chisel into the concrete floor to do any repair. The electrical and HVAC also will be run through the ceiling/attic space and walls unlike a crawl space where we can access them from beneath our home.

Remember that a slab foundation also means our first floor, so our house is close to the moist ground below it. If we live in a colder climate then we can also notice that the flooring on top of its hard surface can feel cold and hard.

A basement is a mixture of both. One of the main differences compared to crawl space is the height. Basement usually have high ceiling so that people can walk around whereas crawl spaces mostly range from one to four feet. Other differences is that crawl spaces are uninhabitable.

difference between crawl space and slab

Water is a foundation's number one enemy. A house can experience movement, therefore water should be kept away from the foundation once the initial drainage is established.

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