The footing depth for a house depends on various factors such as soil type, local building codes, and the weight of the structure. Generally, for one to three-story houses, footings are often in the range of 1.5 to 2.5 meters (5 to 8 feet). For larger structures like four or five-story houses, deeper footings may be required, and specific engineering calculations should be done to determine the appropriate depth based on site conditions.
Depth of footing important factor in building construction,it depends on various factor bearing capacity of soil, number of columns, total dead and live load and other loading and structural aspects of construction. Without knowing bearing capacity of soil and load coming over it, we can only predicting the depth of footing.
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Depth of foundation depends on soil condition, type of soil, hard starta beneath the ground level and safe bearing capacity of soil, type of construction like wall, live load and dead load. When all coming load on footing will be 300KN/floor and safe bearing capacity (SBC) is 250KN/m2, generally footing size 1.5m×1.5m to 2m×2m is applicable.
Depth of footing or foundation ranging between 3 feet to 9 feet (1 metre to 3 metre) deep beneath the ground level for 1 (G+0), 2 (G+1), 3 (G+2), 4 (G+3), 5 (G+4), 6 (G+5) and 7 (G+6) storey/ story building, depending on soil types and load calculation. Footing size for residential building depth should be not less than 3 feet on strong bearing capacity of soil like gravel and sand.
Width and depth of foundation calculated on the basis of safe bearing capacity of soil, type of soil and all the live and dead load coming on it,without knowing bearing capacity of soil and load coming over it, we can only predicting the depth of footing. Actual size is calculated by structural engineer by measuring the safe bearing capacity of soil and all the load coming on it. In this article we use various Thumb Rule for footing depth for 1 to 5 storey building/house
Footings are an important part of foundation construction. They are typically made of concrete with rebar reinforcement that has been poured into an excavated trench. The purpose of footings is to support the foundation and prevent settling and it safely transfer the all coming load to bed of soil.
In geotechnical engineering, bearing capacity is the capacity of soil to support the loads applied to the footing. The bearing capacity of soil is the maximum average contact pressure between the foundation and the soil which should not produce shear failure in the soil.
For the stability of your building concrete structure, you would like to have soil that has good bearing capacity. Gravel and sand are the soils with higher bearing capacity while silts and clays typically have lower capacities.
As UK practices Rule of thumb for foundation depth should be placed at least 450 mm below the finished ground level to avoid the risk of the bearing strata freezing and causing damaging movement.
Rule of thumb for foundation depth uk:- as per thumb rule, for UK practices, Pad foundation or Strip, trench fill foundations must be cast at a minimum depth of 750 mm (0.75 metre) in low plasticity clays, 900mm (0.9m) depth in medium clay, and British Standard 8004 recommends a minimum depth of 1m for foundations in the highest risk areas. If there are trees nearby, depths of foundation up to 3000mm (3 metre) may be necessary.
Footing depth for 1, 2, 3, 4 and 5 storey building
Depth of footing for foundation depends on various factor bearing capacity of soil, number of columns, total dead and live load and other loading and structural aspects of construction. Without knowing bearing capacity of soil and load coming over it, we can only predicting the depth of footing by thumb rule.
In general, the minimum depth of footing required for a single storey building need to be 3 feet deep, while footing depth for a 2 storey building need to be 4 feet deep. Likewise, footing depth for a 3 storey building need to be 5 feet deep, while footing depth for a 4 storey building need to be 6 feet deep. In addition, footing depth for a 5 storey building need to be 7 feet deep.
Foundation depth for 1 storey (G+0) building
The minimum foundation depth for a one storey residential building (G+0) is approximately 3 feet (or 1 meter). For a one-storey residential building, you need a foundation 3 feet (1 meter) deep.
For 1 storey (G+0) house or in simple ground floor building, general thumb rule, using standard 9″ thick walls, we recommended to use depth of footing minimum 3′ (1m) beneath the ground level for isolated footing shallow foundation in gravel and sand soil with higher bearing capacity and size of footing should be 3′ × 3’× 3′ (1m x 1m×1m) provided with Mesh bar of T10@6″C/C of Fe500 Steel with m20 grade of concrete and minimum column size 9″×9″.
Footing depth for 2 storey (G+1) building
The minimum foundation depth for a 2 storey residential building (G+1) is approximately 4 feet (or 1.2 meters). For a two-storey residential building, you need a foundation 4 feet (1.2 meters) deep.
For 2 storey (G+1) house or in simple 2 floor building, general thumb rule, using standard 9″ thick walls, we recommended to use depth of footing minimum 4‘ (1.2m) beneath the ground level for isolated footing shallow foundation in gravel and sand soil with higher bearing capacity and size of footing should be 4’×4’×4′ (1.2m x 1.2m×1.2m) provided with Mesh bar of T10@6″C/C of Fe500 Steel with m20 grade of concrete and minimum column size 9″×12″.
Footing depth for 3 storey (G+2) building
The minimum foundation depth for a 3 storey residential building (G+2) is approximately 5 feet (or 1.5 meters). For a three-storey residential building, you need a foundation 5 feet (1.5 meters) deep.
For 3 storey (G+2) house or in simple 3 floor building, general thumb rule, using standard 9″ thick walls, we recommended to use depth of footing minimum 5′ (1.5m) beneath the ground level for isolated footing shallow foundation in gravel and sand soil with higher bearing capacity and size of footing should be 5’×5’×5′ (1.5m x 1.5m×1.5m) provided with Mesh bar of T12@6″C/C of Fe500 Steel with m20 grade of concrete and minimum column size 12″×12″.
Footing depth for 4 storey (G+3) building
The minimum foundation depth for a 4 storey residential building (G+3) is approximately 6 feet (or 1.8 meters). For a four-storey residential building, you need a foundation 6 feet (1.8 meters) deep.
For 4 storey (G+3) house or in simple 4 floor building, general thumb rule, using standard 9″ thick walls, we recommended to use depth of footing minimum 6′ (1.8m) beneath the ground level for isolated footing shallow foundation in gravel and sand soil with higher bearing capacity and size of footing should be 6’×6’×6′ (1.8m x 1.8m×1.8m) provided with Mesh bar of T16@6″C/C of Fe500 Steel with m20 grade of concrete and minimum column size 12″×16″.
Footing depth for 5 storey (G+4) building
The minimum foundation depth for a 5 storey residential building (G+4) is approximately 7 feet (or 2.1 meters). For a five-storey residential building, you need a foundation 7 feet (2.1 meters) deep.
For 5 storey (G+4) house or in simple 5 floor building, general thumb rule, using standard 9″ thick walls, we recommended to use depth of footing minimum 7′ (2m) beneath the ground level for isolated footing shallow foundation in gravel and sand soil with higher bearing capacity and size of footing should be 7’×7’×7′ (2m x 2m×2m) provided with Mesh bar of T16@6″C/C of Fe500 Steel with m20 grade of concrete and minimum column size 12″×18″.
Conclusions:-
In general, the minimum foundation depth is 1 meter (3.5 feet) for a one-storey building in medium clay soil, 4 feet (1.2 m) for a 2 storey building, 5 feet (1.5 m) for a 3 storey building, 6 feet (1.8 m) for a 4 storey building, and 7 feet (2.1 m) for a 5 storey building.