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crawl space required, residential

Ed Spencer

Registered User
Joined
Oct 4, 2017
Messages
14
Location
Portland Oregon
My client wants to capture a covered patio with slab on grade that is about 16" below the existing finished floor. I can get a vapor barrier and plenty of insulation, but cannot achieve the required clearance for a crawl space. There will be no plumbing in this area but will extend heating ducts. Are we required to provide the minimum clearance? The code is silent on this. Cheers! Ed
 
The code requires that a crawl space be provided where a framed floor exists.

That said, some AHJ will allow you to omit the crawlspace if the wood framed floor consists of joists bearing upon PT sleepers that sit on the existing slab-on-grade. They may require that the joist cavity be separated by a vapor barrier, and that no plumbing, mechanical, or electrical be run in the floor.

I suggest that you develop a plan, and then run it past the AHJ.

R408.4 Access
Access shall be provided to all under-floor spaces. Access openings through the floor shall be a minimum of 18 inches by 24 inches (457 mm by 610 mm). Openings through a perimeter wall shall be not less than 16 inches by 24 inches (407 mm by 610 mm). Where any portion of the through-wall access is below grade, an areaway not less than 16 inches by 24 inches (407 mm by 610 mm) shall be provided. The bottom of the areaway shall be below the threshold of the access opening. Through wall access openings shall not be located under a door to the residence. See Section M1305.1.4 for access requirements where mechanical equipment is located under floors.
 
The code requires that a crawl space be provided where a framed floor exists.

That said, some AHJ will allow you to omit the crawlspace if the wood framed floor consists of joists bearing upon PT sleepers that sit on the existing slab-on-grade. They may require that the joist cavity be separated by a vapor barrier, and that no plumbing, mechanical, or electrical be run in the floor.

I suggest that you develop a plan, and then run it past the AHJ.

R408.4 Access
Access shall be provided to all under-floor spaces. Access openings through the floor shall be a minimum of 18 inches by 24 inches (457 mm by 610 mm). Openings through a perimeter wall shall be not less than 16 inches by 24 inches (407 mm by 610 mm). Where any portion of the through-wall access is below grade, an areaway not less than 16 inches by 24 inches (407 mm by 610 mm) shall be provided. The bottom of the areaway shall be below the threshold of the access opening. Through wall access openings shall not be located under a door to the residence. See Section M1305.1.4 for access requirements where mechanical equipment is located under floors.


How does this require a crawl space? This section just requires access to a crawl space.
 
An 18x24 scuttle in the floor.....
An 18x24 scuttle in the floor gets you access to the entire under floor space? How long are your arms? I may be able to reach a foot or two beyond the scuttle opening.

How is that access to ALL under-floor spaces?
 
You showed us the code section that requires a way to get into a crawl space. Show me the section that requires the crawl space for a framed home. Did you ever see a framed house built on a concrete pad?
 
You showed us the code section that requires a way to get into a crawl space. Show me the section that requires the crawl space for a framed home. Did you ever see a framed house built on a concrete pad?
As in a slab-on-grade home? There is no underfloor space, thus no access requirement.

If you are referring to a framed floor over a slab, then that is not typical prescriptive construction. Hence, why I suggested speaking with the AHJ to get their requirements.

That said, some AHJ will allow you to omit the crawlspace if the wood framed floor consists of joists bearing upon PT sleepers that sit on the existing slab-on-grade. They may require that the joist cavity be separated by a vapor barrier, and that no plumbing, mechanical, or electrical be run in the floor.
 
The only clearances I can find (CA) has to do with earth to wood separation. If your joists are not PT or redwood, the bottoms need to be 18" away from the earth (girders can be 12"). On one job, I specified a "rat slab"..... lean, unreinforced concrete...2" thick poured in the crawl space, and the AHJ then allowed 12" crawl clearance.
 
Minimum clearance is probably determined by required clearances for equipment access, or IRC 317.1 (12" for girders, 18" for joists) for untreated wood. In this case all floor framing & subflooring should be treated, since it will be impossible to inspect or retreat for termites.
 
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