Adjusting Footing Width & Depth for Building Widths Beyond 32 Feet

Footing width and depth must be adjusted if a building's width, perpendicular to the wall footing, is either less than or greater than 32 feet. For every 4 feet a building is narrower than 32 feet, the footing width can decrease by 2 inches and depth by 1 inch, down to minimums. For every 4 feet a building is wider, the footing width must increase by 2 inches and depth by 1 inch.

Footing width and depth must be adjusted from standard 32-foot building recommendations: decrease by 2 inches width/1 inch depth per 4 feet narrower (min. 12" width/6" depth), or increase by 2 inches width/1 inch depth per 4 feet wider.

When designing or constructing footings for residential buildings, the building's overall width plays a crucial role in determining the appropriate footing dimensions. Standard footing tables often base their recommendations on a 32-foot building width, so adjustments are necessary for wider or narrower structures in Southern California.

Adjusting Footings for Buildings Narrower Than 32 Feet

If your building's width, measured perpendicular to the wall footing, is less than 32 feet, you might be able to decrease the footing dimensions. For every 4 feet the building width decreases below 32 feet, the footing width can be reduced by 2 inches, and the footing depth can decrease by 1 inch. This allows for some efficiency on smaller structures, but there are limits. The final footing width must not be less than 12 inches, and the depth must not be less than 6 inches.

For example, if your building is 28 feet wide (4 feet less than 32 feet), you could potentially reduce the footing width by 2 inches and the depth by 1 inch from standard code table values.

> Pro Tip: While code may allow for smaller footings on narrower buildings, always consult with a structural engineer or your local building department. They can confirm the specific allowances for your project and soil conditions, especially in Southern California's varied seismic zones.

Adjusting Footings for Buildings Wider Than 32 Feet

Conversely, if your building's width perpendicular to the wall footing is greater than 32 feet, you'll need to increase your footing dimensions to adequately support the heavier loads. For every 4 feet the building width increases beyond 32 feet, the footing width must increase by 2 inches and the footing depth must increase by 1 inch. These increases are mandatory to ensure the footing can safely distribute the additional weight from a larger structure to the soil below.

For instance, a building that is 36 feet wide (4 feet wider than 32 feet) would require a footing width that is 2 inches greater and a footing depth that is 1 inch greater than what a typical 32-foot building would require. The principles for footing design are critical for the overall stability of your structure, particularly in seismic-active areas like Southern California.

Importance of Professional Design and Code Compliance

These adjustments are generally tied to prescriptive code tables, which use a 32-foot building width as a baseline. However, these tables often assume certain soil bearing capacities and loading conditions. In Southern California, soil conditions can vary greatly, from stable bedrock to expansive clay soils found in areas like the inland valleys. If your soil conditions are poor or if your structure has unusual loads, a custom engineering design will always be necessary.

Minimum overall footing width is 12 inches and minimum thickness is 6 inches, regardless of any permitted decreases for narrower buildings. For required interior braced wall panels in Seismic Design Categories D0, D1, and D2 with plan dimensions greater than 50 feet, continuous masonry or concrete footings are mandatory.

For more detailed information on specific footing requirements in our region, you might find our articles on Minimum Width and Thickness for Concrete Footings in SoCal and Continuous Footing Requirements in SoCal Seismic Zones D0, D1, D2 helpful. You can also review our dedicated services page for Retaining Walls & Footings.

Before undertaking any foundation work, verify your proposed footing design with local building officials and consider a geotechnical report for site-specific soil analysis. This ensures compliance with all local codes and guarantees a safe, durable foundation for your Southern California property. Contact Western Concrete to discuss your foundation project and get expert advice tailored to your needs.