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.
Depending on your local building code and whether you have a basement, that might be 5-10 feet below grade. Footings are required to be built on undisturbed soil.
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).
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).
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.
According to the rule of practice, the minimum allowable rebar diameter in a footing is Ø12 and the maximum acceptable spacing between the reinforcement bars is 150 mm. In certain occasions, the footing may have a reinforcement wire mesh both at its upper surface (see following figures).
Even the best contractors occasionally have to build on a sloppy footing. Ian Geisler, a noted ICF expert who has worked on hundreds of projects across the continent, says that realistically a perfect footing is anything within ¼” of level. “If it's within ½”, then it's workable,” he writes.
To determine the size of the footing, a simple formula is used: Structural Load (lbs) / Soil Capacity (psf) = Footing Surface Area Required (sq. ft.)
When measuring for where to place your footers, make sure that the holes will be square with your house and that they are are no more than 8-feet apart in either direction. This is a general recommendation to keep your deck as sturdy as possible.
Depth of Footings
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.
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.
Between your foundation walls and resting on top of the footings lies your foundation slab: the giant piece of concrete which makes up your basement floor or subfloor. Each of these pieces must be poured and cure one at a time: a process that can take up to a week for each step.
The footing depth, on the other hand, is typically determined by the soil type and the extent to which you must dig before striking undisturbed soil. Still, we recommend that the depth of the footing extends to a minimum of 12 inches after you've hit undisturbed soil.
Deck pier blocks are used in deck building as an alternative foundation to traditional footings. They are placed directly on the ground, and do not require digging or pouring. They come pre-formed with holes for attaching the posts of a deck, making it easy to install.
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.
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).
According to an example cited on TATA Tiscon site, if a 3-storeyed building rests on sandy soil, it will require minimum 5.5x5. 5 feet to 6x6 feet footing size. Similarly, a 2-storeyed one requires 5x5 feet and single storied will need 4x4 feet footing size.
Minimum foundation depths should be measured from the reduced level where the reduced level will be the finished ground level.
Use compaction whenever the soil is disturbed during construction or when it's used for fill. Compact disturbed soil beneath footings, slabs, basement floors, patios, garage floors, driveways, concrete steps and sidewalks. If a sand, gravel, or crushed stone base is used beneath a slab, compact it too.
The section on footings in Formwork for Concrete (ACI SP-4) says that when fabricated forms are omitted entirely and concrete is cast directly against the excavation, larger tolerances may apply. The book also suggests forming the top 4 inches when casting concrete directly against earth.
❖ Footings are required to extend below the ground surface a minimum of 12 inches (305 mm). This is considered a minimum depth to protect the footing from movement of the soil caused by freezing and thawing in mild climate areas.
While 8 to 10 feet apart is a sufficient distance for foundation piers to support most structures that would sit atop a post and pier foundation, if the building is particularly tall or made of heavier materials such as brick or metal, it's not uncommon to place the foundation piers even closer together.
Footing thickness - 8 to 12 inches.
1) There is no hard minimum for the spacing between footings. Hence the raft foundation logic. 2) Depending on the soil properties, footings placed close together may need to be designed to a lower bearing stress in order to limit settlement equivalently.