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What are the different types of house foundation types and when to use each?

By Kevin Carden Published 06/30/2007 | Home Improvement

The foundation is the first piece of a home to be constructed and creates a base for the rest of a home's components. There are three types of foundations that are commonly used in the U.S.: slab, crawlspace, and basement.

Slab Foundation

Slab is a type of foundation consisting of a structural concrete slab poured directly on the grade. No accessible space exists in slab construction. Slab foundations are popular in areas (i.e. the Southern United States) where there is a relatively high water table. (Water table refers to the depth in the soil at which you find water).

Crawlspace Foundation

A crawlspace is an accessible space with limited headroom, typically between the soil and the bottom of the first floor of a home. Crawlspace construction is predominant in areas where there is heavy clay content in the soil.

Basement Foundation

A basement is an accessible space between the soil and the bottom of the first floor of a home. It usually has more headroom than a crawlspace. Basement foundation construction is predominant in cold climates where the foundation needs to be situated below the frost level.

All three foundation types are usually constructed out of concrete, but can also use concrete masonry units or insulated concrete forms.

Concrete Masonry Units (CMUs) are hollow, concrete blocks. To create the foundation wall, mortar is used between blocks to hold them together, forming the wall.

Insulated Concrete Forms (ICFs) are made of rigid foam insulation forms (a system of support assemblies, including mold, hardware, and necessary bracing to hold concrete) into which concrete is poured. Once the concrete has gained its full strength, the outside forms, the inside forms, or both are left in place to insulate the wall. ICFs are common in regions in which the local building code requires the foundation to be insulated. Another benefit is that the homeowner or builder is able to finish basement immediately, without adding studs.

Choosing the Type of Foundation:

Homeowners and builders make decisions about which type of foundation to use by gauging cost, needs/desires, and soil and weather conditions. If you have high water tables then it may not be possible to have a basement. If your land has shallow bedrock or boulders then it may be more costly to dig a basement. If you have a sloping lot it may be difficult to use a slab foundation. If you have a cold climate then you may need to dig down at least four or more feet to put the home's footings below frost level. If you have to go at least four feet deep then it may be worth spending some extra money to dig a few feet deeper and have a full basement. Also, it is easier to install and maintain mechanical systems in basements (compared to a crawlspace). Your builder can help you determine what type of foundation is best suited for your area.

The choice of foundation is also affected by personal preferences and costs. Basements can add thousands of dollars to the cost of a home compared to the cost of a crawlspace. However, when you consider the extra useable space created by a basement it is some of the cheapest square footage space of a home. If you are tight on funds and can't afford the basement then it may be a good idea to find a slightly smaller plan and use the savings to create a basement. You'll end up with a lot more storage space and potential living space by doing this.

Changing the Type of Foundation on your home:

Almost any house plan can have its foundation changed. It's common for people to design a different foundation if the available foundations do not suit their needs. If you are currently working with a builder you may want to ask them if they will take care of making the foundation changes for you. Sometimes with foundation design it may be helpful for somebody who is near you to do those changes because they will have more knowledge about your local soil conditions and the slope of your lot.

When changing foundation types, pay attention to where you will put the furnace, water heater, and stairs. If you need to add basement stairs, the basement stairs can usually be put under other stairways or you may be able to replace a closet or small room with basement stairs. Another common place to put basement stairs is to replace a mechanical room with stairs and move the mechanical items (such as the furnace and water heater) to the basement. Sometimes space near the laundry room, or space near the garage can be used for a basement stairs. Larger walk-in closets are sometimes reduced in size to allow space for basement stairs. You can often add a basement stairs to a plan without increasing the size of the plan. However, sometimes space may need to be added to a plan to provide room for a basement stairs.

It should be noted that it is the owner's full responsibility to check with his/her local and state building authorities, his/her builder, and the designer of the house plan to ensure that the home meets all applicable building codes and requirements.

Mark Mathis is a building designer and publisher of several stock house plan websites and informational resources, the most famous being <a href=http://www.HousePlanCentral.com>www.houseplancentral.com</a>.  House Plan Central has a large collection of home plans and unique house plans in many different architectural styles, from the nation's top house designers and architects.