Crawlspace venting requirements: Commercial vs. Residential

[Robert]

I currently have a 1920's commercial space (kitchen in CA, mild climate) that has a wood floor over a crawlspace completely below grade. We excavated to achieve 18" min. clearance and added a floor hatch (this is a plumbing repair and complete floor replacement job). My questions are about venting. In an unvented scenario, Residential code allows vapor barrier over earth with a dehumidifier installed (section R408.3.2.2.4). However, when I get to CBC (commercial) they do not have a dehumidifier as an option, and seem to require either making the crawlspace conditioned and insulating the perimeter, or needing vapor barrier over the earth and adding venting (CBC 1202.4.).

Questions: if the crawlspace floor above does not have insulation, but does not directly communicate with the space above (ie. a floor vent), is that considered conditioned space? And they mention the walls of the crawlspace need to be insulated....but in this case there are no walls, just concrete stemwall up to above grade, so are we allowed to call this conditioned spacee without adding any insulation to the exterior stemwalls?

As another option the CBC does allow mechanical ventilation, but that might be different from a dehumidifier as mentioned in the CRC? Can the residential solution apply in this case using a dehumidifier? The issue is difficulty in adding exterior vents (it's below grade with concrete stemwalls and impossible to get cross ventilation on one end of the crawlspace). Thanks for any insights.

 

[steveray]

Are you replacing the floor because it rotted out? Ask the AHJ for alternatives?

 

[MtnArch]

If you have a commercial space you cannot use the CRC. You cannot pick and choose to flip/flop back and forth between CBC and CRC to suit your ideas and/or design.

 

[Robert]

Are you replacing the floor because it rotted out? Ask the AHJ for alternatives?

Yes. I'm wondering why the CRC allows a dehumidifier in place of venting for situations like this, but the CBC does not.

 

[Robert]

Are you replacing the floor because it rotted out? Ask the AHJ for alternatives?

I already specified the dehumidifier in the drawings with no venting and they approved it. Technically not to code, and they did not ask for an AMMR. I don't know any other options. Perhaps if this is considered conditioned space, it might be to code with no venting. Most of the floor damage was from a plumbing leak, so now that we have a floor hatch, vapor barrier and dehumidifier, it's a better crawlspace then before. I know some of these old buildings have these shallow crawlspaces, like 12"....like bathtubs, and wondering what others have done when they can't vent.