Typical Footing Width for a House

Footings

• Don't confuse footings with the foundation of a home. A foundation stands on footings, which transfer the load of the house to a stable rock or solid-soil layer under the house. Footings are crucial in areas with soft soils or where the soil freezes during the winter. Such instances can lead to shifting soils, and a footing is needed to extend below the frost level or to bedrock for a firm foundation support. Footings range from nonexistent to 32 inches wide, depending on various factors. According to Mark R. Miller in "Miller's Guide to Foundations and Sitework," the average footing width is 8 inches.

Soil Density

• The density of the soil surrounding a foundation plays a significant role in choosing the width for footings. Softer soils need a wider footings. The minimum bearing capacity for soil to build a house upon should be 1,500 lbs. per square foot, according to the Homeland Security Department's "Homebuilders Guide to Earthquake Resistant Design and Construction." This soft soil requires a footing with width of at least 12 inches to properly support the house. The minimum required width for footings decreases as the soil density increases.

House Size

• The weight and size of a structure determine the vertical load put on the footings. Taller homes need wider footings to support the additional load because they are heavier than single-story homes. Engineers consider the load the footings must support and the soil density to choose footing width. Tables from engineering manuals are used to determine the width of the footings based on your soil bearing capacity and the load of your house. For instance, if your home has a load of 1,000 lbs. per linear foot of footing on footings in soil with a bearing capacity of 2,500 lbs. per square foot, your footings should be 5 inches wide, according to "Building an Affordable House: Trade Secrets to High-Value, Low-Cost Construction" by Fernando Pagés Ruiz. Get an engineer to determine the load placed on the footings and the soil density to be certain you have the correct calculations. Your entire house will depend on these numbers being correct.

Foundation Thickness

• Some use the thickness of the foundation as a rule of thumb for estimating the width of footings. A footing is shaped like an upside down T. The footing's width is the crossbar of the T-shape. According to "Real Estate Home Inspection: Mastering the Profession," by Russell W. Burgess, this averages twice the width of the foundation wall. Start with this estimate as a guideline but use the more precise calculations based on the soil-bearing capacity and your home's size.

When Footings Are Not Needed

• Not every home requires footings. The foundation acts as the footing for a home in a warm climate, but only if the surrounding soil will allow it, according to Russell W. Burgess in "Real Estate Home Inspection: Mastering the Profession." Check with an engineer and consult your local building codes before constructing a home without footings.