How far below the adjoining grade must the passageway depth be before specific wall lining is required?

The requirement for a specific wall lining in a passageway is set to ensure safety and durability in areas that may be exposed to moisture or other damaging elements. When the depth of a passageway is below the adjoining grade by 12 inches, it becomes susceptible to water infiltration and potential damage from moisture. To mitigate these risks and protect the structural integrity of the installation, specific wall lining is mandated at this depth.

This precaution helps to maintain a safe environment by preventing mold, decay, or other issues that could arise from prolonged moisture exposure. This requirement serves as a critical guideline in mechanical and construction practices, reinforcing the importance of proper grading and protective measures in building design.