Residential Building Inspector B1Footings and FoundationsMedium
A builder is preparing to backfill around a new foundation wall. The foundation is properly dampproofed, and a foundation drain has been installed. According to the 2021 IRC, what type of material is required for the first 6 inches of backfill directly above the foundation drain?
- ANative excavated soil
- BClay soil
- CSand or gravel
- DCompacted fill dirt
Show answer & explanationAnswer & explanation
Correct answer: C. Sand or gravel
IRC R405.1 specifies that the backfill over the drainage tile or crushed stone shall be crushed stone or gravel to a minimum depth of 6 inches above the drain tile.
Why the other options are wrong
- A. Incorrect. Native excavated soil might contain clay or other fine particles that prevent proper drainage.
- B. Incorrect. Clay soil would impede drainage, defeating the purpose of the foundation drain.
- D. Incorrect. While compacted fill dirt is generally used for backfill, the critical first 6 inches above the drain must be granular material for drainage.
Foundation Drain Backfill Material
The specific type of granular material required directly above a foundation drain to ensure proper water flow and prevent clogging.
- IRC R405.1 regulates foundation drainage.
- Crushed stone or gravel is required.
- Must extend at least 6 inches above the drain.
- Prevents fine soils from clogging the drain.
Memory trick: Drainage needs gravel on top, like a crunchy cereal, for water to flow free.