What is the minimum slope for ducts installed underground to allow drainage?

The minimum slope for ducts installed underground to allow drainage is 1/8 inch per foot. This slope ensures that any water accumulating within the duct has a proper pathway to drain out, thus preventing water buildup that could lead to corrosion, blockages, or damage to the ducting system.

A slope of 1/8 inch per foot is generally considered adequate for maintaining proper drainage without being excessively steep, which could complicate installation and potentially lead to other operational issues. This guideline is often cited in building codes and standards to ensure effective drainage in underground applications.

Higher slopes, such as 1/4 inch per foot or more, may be beneficial in certain conditions but are not strictly necessary for the effectiveness of drainage and can introduce installation challenges.