A carpenter is preparing to pour a residential concrete footing. The local building code specifies a minimum footing depth of 450 mm below undisturbed grade in this region. The existing grade is 200 mm above the proposed top of footing. What is the minimum excavation depth required from the existing grade?

Question: A carpenter is preparing to pour a residential concrete footing. The local building code specifies a minimum footing depth of 450 mm below undisturbed grade in this region. The existing grade is 200 mm above the proposed top of footing. What is the minimum excavation depth required from the existing grade?

Answer options:

• 250 mm
• 450 mm ✅ 650 mm
• 700 mm

Correct answer: 650 mm

Explanation: To determine the minimum excavation depth from existing grade, you add the required footing depth below undisturbed grade (450 mm) to the distance the existing grade is above the proposed top of footing (200 mm). This totals 650 mm. If only 250 mm was excavated, the footing would not meet the required depth below grade.