Residential Building Inspector B1Footings and FoundationsMedium
A building inspector is examining the foundation of a new residential structure. The foundation drain is installed with a perforated pipe. What is the minimum required diameter for this perforated pipe, according to the 2021 IRC?
- A3 inches (76 mm)
- B4 inches (102 mm)
- C6 inches (152 mm)
- D2 inches (51 mm)
Show answer & explanationAnswer & explanation
Correct answer: B. 4 inches (102 mm)
IRC Section R405.1 specifies that perforated pipe used for foundation drains shall be not less than 4 inches (102 mm) in diameter.
Why the other options are wrong
- A. While used in some applications, 3 inches is below the minimum required for a foundation drain.
- C. This diameter is larger than the minimum required and would be acceptable, but not the minimum.
- D. This diameter is too small for a foundation drain and would not be permitted by the IRC.
Foundation Drain Pipe Diameter
The minimum required diameter for perforated pipe used as a foundation drain to collect and remove groundwater.
- IRC R405.1 specifies a minimum of 4 inches (102 mm).
- Ensures adequate flow capacity for collected water.
- Pipe must be installed with proper slope and surrounded by gravel.
Memory trick: Drain pipe: four inches wide, keeps the water on the outside.