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.
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.
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.
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).
The thickness (T) of the foundation should be:
150mm to 500mm for strip foundation. 500mm minimum for trench fill foundations.
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.
The thickness of the footings should be not less than 200mm and is usually mass concrete only, ie. no reinforcement. The depth below ground level to the base of the footing should be not less than 300mm or to rock, whichever occurs first, which allows for a minimum of 100mm of ground cover to the pad.
Deep Strip Footing
A reinforced concrete strip supports the walls. The trench can be of any depth, but it should be at least 40 inches deep and 24 inches broad. Concrete should have a minimum depth of 9 inches.
Footings should extend to a minimum depth of 12 inches below previously undisturbed soil. Footings must also extend at least 12 inches below the frost line (the depth to which the ground freezes in winter) or be frost-protected.
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.
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).
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.
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.
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).
1.3, as applicable, but not less than 12 inches (305 mm) in width and 6 inches (152 mm) in depth . The footing width shall be based on the load-bearing value of the soil in accordance with Table R401. 4.1. Footing projections, P, shall be not less than 2 inches (51 mm) and shall not exceed the thickness of the footing.
What is the minimum depth of shallow and deep foundations? Shallow foundations have a minimum depth of around 1 metre, while deep foundations usually start at depths exceeding 3 metres.
The depth of the footing hole depends on the type of soil and the size of the building. The hole must be deep enough so that the footing is below the freeze line (the depth at which water in the ground freezes) and above any soft or loose soils. Once the hole is dug, the footing must be created.
The region and wind zone that you are building in will dictate what is required by your local state and county codes. Areas that are seismically active definitely require steel rebar in the footing construction.
Design Steps as per IS Code
As per IS 456:2000, the following are the steps involved in designing an isolated footing: The area of footing is calculated based on the factored column load. Net soil pressure is then calculated, and net factored soil pressure is found. The effective depth of footing is calculated.
In reinforced and plain concrete footings, the thickness at the edge shall be not less than 150 mm for footings on soils.
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.
According to IRC Section R403. 1.2, "The top of the footing shall be at least 12 inches below grade and at least 6 inches below the undisturbed soil surface."
The thickness of a strip foundation should be between 150mm and 500mm. 300mm thickness is used in most small domestic works.
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).
It is generally economical to vary the thickness of the slab from a minimum of 150 mm at the edges to a maximum near the face of the column depending upon the variations in bending moment and shear force. A leveling course of lean concrete of 100 mm thickness is generally provided below the footing.