How thick must concrete encase metallic underground ducts without an approved protective coating?

When it comes to protecting metallic underground ducts, the thickness of concrete encasement plays a crucial role in ensuring durability and preventing corrosion. In the context of the North Carolina Mechanical Code, a thickness of 2 inches of concrete provides a sufficient barrier to protect the metallic ducts from external impacts, moisture, and soil chemicals that could lead to corrosion.

This standard is established to ensure that the integrity of the ductwork is maintained over time, considering the harsh conditions they may be subjected to when buried underground. A thinner layer might not offer adequate protection, potentially leading to deterioration and failures, while a thicker layer, although providing additional protection, could be excessive and unnecessarily cumbersome.

The requirement for a 2-inch encasement strikes a balance between effective protection and practical implementation, making it the correct choice when no approved protective coating is applied. This helps ensure safety and longevity for the underground duct systems in accordance with the relevant mechanical and building codes.