Residential Building Inspector B1Footings and FoundationsEasy
A building inspector is reviewing plans for a new residential structure. The plans indicate that the soil under the footings has a presumptive load-bearing value of 1,500 psf. The proposed continuous footing is 16 inches wide and supports a wall with a design load of 1,200 pounds per linear foot (plf). Based on the 2021 IRC, what is the minimum required width for this footing?
- A12 inches
- B10 inches
- C16 inches
- D8 inches
Show answer & explanationAnswer & explanation
Correct answer: B. 10 inches
To determine the minimum required footing width, divide the design load per linear foot by the presumptive load-bearing value of the soil. 1,200 plf / 1,500 psf = 0.8 feet. Convert to inches: 0.8 feet * 12 inches/foot = 9.6 inches. Since footings must be at least 10 inches wide according to IRC Table R403.1, the minimum required width is 10 inches.
Why the other options are wrong
- A. While acceptable, it's not the minimum required width.
- C. This is the proposed width, which is more than the minimum required, but not the calculated minimum.
- D. This width is less than the calculated minimum and the IRC minimum.
Footing Width Calculation
The minimum width of a footing is determined by dividing the design load per linear foot by the presumptive load-bearing value of the soil, ensuring it meets or exceeds IRC minimums.
- IRC Table R403.1 provides presumptive load-bearing values.
- Calculated width must be rounded up to the nearest whole inch or standard dimension.
- IRC specifies minimum footing widths regardless of calculation.
Memory trick: Load on the ground, width all around.