What is the minimum height above ground for wood floor joists and girders/beams?
Wednesday, March 6, 2019
The minimum clearance between the ground and the wood structural floor joists and girders is primarily for prevention of wood rot that is caused by wood being too close to the moisture in the soil. So the minimum is 18” for floor joists and 12” for wood beams within the building foundation, according to the Internaitonal Residential Code (IRC) and the Residential Edition of the Florida Building Code [FBC R317.1 (1)], UNLESS the wood is preservative-treated or naturally durable. The species that are classified as “naturally durable” are the heartwood of redwood, cedar, black locust, and black walnut.
Although the 18” and 12” minimum clearances are exempted for preservative-treated and naturally durable wood, they are also the minimum heights that make a crawl space reasonably accessible for inspection or repair. Unfortunately, when a crawl space is further obstructed by ducts and piping, like in photo below, access to much of the crawl space can be impossible without digging under the obstructions.
Also, see our blog post What does a home inspector look for in the crawl space under a home?
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