What is the maximum depth a trench installed parallel to footings can extend below?

The maximum depth a trench installed parallel to footings is allowed to extend below is determined by the concept of lateral support and the safety of the structural elements involved. When a trench is dug adjacent to a footing, it is essential to maintain stability and prevent potential soil movement that could undermine the footing or the structure above it.

The IRC specifies that the trench should not extend beyond a 45-degree line from the bottom of the footing. This is to ensure that the weight and structural integrity of the footing are not compromised. The 45-degree angle represents a balance between safety and practicality, allowing sufficient depth for drainage or utility installation while maintaining the integrity of the foundation.

The other options presenting steeper angles, such as 30 degrees, 60 degrees, and 75 degrees, would extend the trench deeper than the IRC allows and could introduce risks of soil collapse or destabilizing lateral support for the foundation elements. Adhering to the 45-degree guideline helps to ensure safety and compliance with best construction practices as outlined in the IRC.