Isolated columns or normally supported by different types of foundations e.g. spread footing, combined footing, pile foundation etc. Design of foundation is a challenging task. A foundation engineer must be careful during designing the building foundation.

Foundation thickness should be determined from one way and two way shear requirement calculation. However, there are code specified minimum value of different type of foundations. Followings are two code references (ACI and BNBC) for minimum thickness value of concrete footing.


Depth of footing above bottom reinforcement shall not be less than 150 mm for footings on soil, nor less than 300 mm for footings on piles.

Section 15.7, ACI 318-08
Type of FootingMinimum ThicknessRemark
Masonry250 mm; twice the maximum projection from the face of the wallGreater of the two values shall be selected
Plain concrete200 mm, or twice the maximum offset in a stepped footing 
Reinforced concrete (depth above bottom reinforcement)
Resting on soil
Resting on pile

N.B. Two storeys or less in Occupancy category A, B, C and D.

Table 6.3.6, BNBC 2006

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