Residential Building Inspector B1Footings and FoundationsMedium
A builder is preparing to backfill around a new foundation wall. The foundation is properly dampproofed. According to the 2021 IRC, what type of material should be used for backfill immediately adjacent to the foundation drain to ensure proper drainage?
- ASilty loam from the excavation
- BPulverized topsoil
- CCompacted native clay soil
- DClean gravel or crushed stone
Show answer & explanationAnswer & explanation
Correct answer: D. Clean gravel or crushed stone
IRC Section R405.1 requires that foundation drains be covered with not less than 6 inches (152 mm) of approved drainage fill, such as clean gravel or crushed stone. This permeable material allows water to easily reach the foundation drain and be carried away.
Why the other options are wrong
- A. Silty loam is too fine and would impede drainage and potentially clog the drain.
- B. Pulverized topsoil is organic and fine-grained, which would also impede drainage and potentially clog the drain.
- C. Compacted clay is impermeable and would trap water, preventing it from reaching the drain.
Foundation Drain Backfill
Foundation drains must be surrounded by a layer of permeable drainage fill, such as clean gravel or crushed stone, to allow groundwater to flow unimpeded into the drain.
- IRC R405.1 specifies drainage fill.
- Material must be clean, permeable, and free of fines.
- Ensures efficient collection and removal of groundwater.
Memory trick: Drainage needs stone, water finds its home.