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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Here’s links to a collection of our other blog posts about STRUCTURE AND ROOMS:

• Why is the grout cracking and coming loose at my floor tile?

• What are the building code requirements for notching and boring holes in a wall stud? 

• What causes dark or light "ghost" lines on ceilings and walls?

• Can you access or exit a bedroom through another bedroom?

• What is the difference between a carport and a garage? 

• What are simple ways to find the cause of a ceiling stain?

• What is the minimum size of habitable rooms in a house according to the building code? 

• Why is my garage ceiling sagging? 

• How can I identify what kind of wood flooring I am looking at?

• Why does my concrete floor slab sweat and get slippery?

• What is the minimum ceiling height for rooms in a house? 

• Why are there score line grooves in the concrete floor of the garage?

• How much can I cut out of a floor joist? 

• How can I tell if my floors are sloping?

• Why do the floors slope in this old house? 

• What are the common problems when a homeowner converts a garage to conditioned living space, such as a family room?

• How can I tell if a wall is load-bearing? Which walls can I take out?   

    Visit our STRUCTURE AND ROOMS page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.