Residential Building Inspector B1Floor ConstructionHard
A residential structure is being constructed with a crawl space. The floor joists are 2x10s. What is the minimum required clearance between the bottom of these wood floor joists and the exposed earth in the crawl space, according to the IRC?
- A12 inches
- B18 inches
- C24 inches
- D6 inches
Show answer & explanationAnswer & explanation
Correct answer: B. 18 inches
IRC R408.3 specifies that the minimum clearance from the bottom of wood floor joists or beams to the exposed earth in a crawl space shall be 18 inches. This clearance is crucial for preventing moisture damage, allowing for ventilation, and providing access for inspection and maintenance.
Why the other options are wrong
- A. This is the minimum clearance for wood girders, not joists, to exposed earth.
- C. While more clearance is beneficial, it's not the minimum required by code.
- D. This is too little clearance and would likely lead to moisture and access issues.
Crawl Space Clearance (Joists)
The minimum vertical distance required by code between unencapsulated earth and the bottom of wood floor joists or beams in a crawl space.
- Prevents moisture migration into wood.
- Allows for adequate ventilation.
- Provides access for future inspections and repairs.
Memory trick: Earth to Wood: 18 for Joists, 12 for Girders.