What is the minimum thickness for a spread footing in inches?

Author: Raphaelle Stoltenberg Jr.  |  Last update: Monday, June 9, 2025

The foundation thickness shall not be less than the following: For spread footings under load bearing walls twelve (12) inches. For spread footings under columns twelve (12) inches. For mat foundations, twelve (12) inches under concrete walls, twelve (12) inches under columns and six (6) inches elsewhere.

What is the minimum thickness for spread footings?

Minimum sizes for footings shall be as set forth in Table R403. 1(3) of the International Residential Code and Figures 402(1) through (4) modified as follows: Spread footings shall be at least 8 inches (203 mm) in thickness.

What is the thumb rule for footing thickness?

Simple Gravel and Concrete Footing Design

The minimum footing thickness should not be less than the distance the footing extends outward from the edge of the foundation wall, or 6 inches, whichever is greater.

How thick should footings be?

Required Footing Sizes

In most cases, a house should have a minimum footing of 12 inches wide by 12 inches deep, with foundations that are 8 to 10 inches thick. This should be enough to support house weight and resist lateral soil and water pressure.

What are the minimum requirements for footings?

The minimum depth of footings below the surface of undisturbed soil, compacted fill material or controlled low strength material (CLSM) shall be 12 inches (305 mm). Where applicable, the requirements of CBC Section 1809.5 shall also be satisfied. The minimum width of footings shall be 12 inches (305 mm).

Sizing a Spread Footing!

What is the minimum thickness of footing on soil?

In reinforced and plain concrete footings, the thickness at the edge shall be not less than 150 mm for footings on soils.

What is the minimum depth for a footing?

A minimum of 12”inches deep for all footings and the width will be determined by the amount of stories, 12” inches for a single story, 15” inches for a two story and 23” inches for a three story. This is based on a soil bearing capacity of 1500(psf).

What is the depth of spread footings?

The depth is determined by the depth of stable soil or bedrock, while the width is calculated based on the load-bearing capacity of the soil. Our standard spread footings typically measure 4'x4'x1'-6” up to 8'x8'x1'-6” thick with columns measuring 24”x24”x4' up to 8' tall.

What is the minimum size of footing?

Concept: For footing: i) The thickness at the edge shall not be less than 150 mm for footings on soil and not less than 300 mm for footing on piles. ii) The depth of the foundation should be a minimum of 500 mm.

What is the difference between a footer and a footing?

Footings are structural supports that are used in addition to a foundation. They help transfer the load's weight from the foundation into the soil. Footers are typically in direct contact with the ground, while the foundation is in contact with the footing.

How do you calculate footing thickness?

To determine the size of the footing, a simple formula is used: Structural Load (lbs) / Soil Capacity (psf) = Footing Surface Area Required (sq. ft.)

What thickness of footings under columns or posts should be?

Footing thickness - 8 to 12 inches. Footing depth - varies based on frost line and soil strength (some footings can be shallow, while other must be deep)

What should be the depth of footing?

All foundations shall extend to a depth of at least 50 cm below the natural ground level. The minimum depth of footing on sandy soil is 0.8 - 1 m, for rocky soil, it is 0.05 - 0.5 m and for clayey soil, it is 0.9 - 1.6 m. The minimum depth of foundation for the load-bearing wall is 900 mm.

What is the rule of thumb for concrete footings?

For every 2 feet of adjustment to the width of the house, add or subtract 2 inches of footing width and 1 inch of footing thickness (but not less than 6 inches thick).

Is spread footing deep or shallow?

Spread footings are types of shallow foundation which transmit and distribute the point load from the structure (column, support) to the soil. The spread footings have been performed as masonry structures of complex rock blocks, bricks and unreinforced concrete.

Do footings spread the weight of a building over a wider area?

Footings function by dispersing the weight on the post over a wider area, thereby reducing the number of pounds per square foot (psf) at any point on the soil surface. By increasing the surface area with a footing, more load can be supported by the same post without settling.

What is the minimum thickness of a footer?

The minimum footing thickness is 6 inches. The minimum footing width is 12 inches. Calculation of footing size may result in a smaller footing but the code requires a minimum 12 x 6 or 12 inches wide and 6 inches deep footing. In addition, tables are based on the type of foundation.

What is the thickness of concrete footings?

In reinforced and plain concrete footings, the thickness at the edge shall be not less than 150 mm for footings on soils. For footings on piles, the thickness at the edge shall be not less than 300 mm (30 cm) above the tops of piles.

What is the minimum thickness at the edge of footing?

In reinforced and plain concrete footings, the thickness at the edge shall be not less than 150 mm for footings on soils. For footings on piles, the thickness at the edge shall be not less than 300 mm (30 cm) above the tops of piles.

What is a typical residential spread footing?

This has to be the most typical foundation type with basement or crawlspace construction. The spread footing design is simple; provide sufficient footing area to distribute the weight of the structure onto the soil. Typically, a 16” wide x 8” concrete footing is used.

How deep are normal footings?

Footings need to be 600mm wide x 1m deep minimum,in some cases depending on ground quality/type,proximity of large trees footings are required to be up to 2m deep.

What is the minimum footing size?

Footings shall be a minimum of 8 inches by 24 inches (203 mm by 610 mm) for houses two and one-half stories and less. The footings for a three-story building shall be 10 inches by 24 inches (254 mm by 610 mm).

How to calculate the thickness of footing?

How thick should footings be? The factors to take into consideration are A- the allowable bearing pressure capacity of the soil, and B= the amount of total weight of the building, placed on the footing, including the foundation and the footing weight, per lineal foot.

Can footings be too deep?

First off: Why you need accurate footings calculations

If you make your foundations too shallow or too deep, there is a risk to the integrity of the build, and a danger that any reinforcement, be it mesh panels or rebar rods, is positioned incorrectly, leading to reduced tensile strength and load-bearing capacity.

What is the minimum thickness of a retaining wall footing?

Moreover, size and depth of foundation should be enough to resist overturning and sliding of wall. As a thumb rule, depth of footing of a free standing wall is usually 1/3 of its height to ensure stability. So for a wall of height 8 ft, its footing should be 2.7 ft deep.

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