Which phrase best describes the required footing depth relative to the frost line given a 24 inch frost line?

Which phrase best describes the required footing depth relative to the frost line given a 24 inch frost line?

• A. above the frost line
• B. at the frost line
• C. below the frost line
• D. well below the frost line

Answer: (C)

Frost protection for foundations is the key idea here: you place footings below the depth that the ground freezes to avoid frost heave. If the frost line is 24 inches, the footing must extend deeper than that depth. That makes “below the frost line” the best choice, because it communicates being under the frozen layer where ground movement from freezing doesn’t occur. Placing the footing above or at the frost line would leave it in the zone that can heave, and “well below” is more depth than typically required.

Frost protection for foundations is the key idea here: you place footings below the depth that the ground freezes to avoid frost heave. If the frost line is 24 inches, the footing must extend deeper than that depth. That makes “below the frost line” the best choice, because it communicates being under the frozen layer where ground movement from freezing doesn’t occur. Placing the footing above or at the frost line would leave it in the zone that can heave, and “well below” is more depth than typically required.