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IRC 2018 Foam plastic specific approval (unvented crawl) question

ChrisInIllinois | Posted in Building Code Questions on

IRC Unvented crawl space R408.3

2.1 Continuous exhaust of crawl with “an air pathway to the common area” from crawl.

This creates negative pressure, but does not seem to be an unvented crawl…..

2.2 “Conditioned air supply” “including a return air pathway to the common area.

2.3 plenum use under floor space.

2.4 Dehumidification sized 70 pints per 1000 sq ft of floor space.

This one is the only one that does not “technically” have an air path to other parts of the house, but to be honest, most crawls have ducts at least in my experience.

Building planning:

R316 Foam Plastic:

R316.5.4 Crawl space exceptions to Thermal barrier (R316.4 )

#3. Foam plastic has been tested in accordance with R316.6 or is protected against ignition.

HOW IS THIS AN EXCEPTION IF YOU MUST USE R316.6 for Specific approval? Lol

R316.6 Specific approval:

Foam plastic not meeting requirements section r316.3 through r316.5 specifically approved basised on one of the following approved test. NFPA 286 with R302.94, RM 4880, UL 1040 or UL1715.

My thoughts:

It seems manufacturers have to have the whole assembly test, just having UL 1040 or 1715 is not enough you need to read the paper and make sure your assembly is like what was tested?

As I read the Code Evaluation Reports for use in crawl spaces I keep coming across this requirement:

Air in crawl space is NOT circulated to other parts of the building”

Based on air moment requirement of  R408.3 this test to allow no  ignition barrier is useless for UNVENTED crawl spaces. At least for the foam company I have found so far.

I am I missing something or am I reading that right?

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  1. Expert Member
    Peter Engle | | #1

    You've pretty much got it right, and you are learning the joys of Codespeak.

    In general, foam used in crawl spaces must have a thermal barrier. If the crawl is used only for service access, you can generally get by with an ignition barrier.

    Some foams, like the one you are investigating try to get sneaky with the language. Since the requirement is that the foam be "separated from the occupied spaces" by the thermal/ignition barrier, some companies argue that the subfloor acts as that separation and they test their foams that way. So, their ESR says that the foam does not require a separate thermal or ignition barrier. But then the fine print says that there can be NO air circulation between the crawl and the house. This is relatively easy to achieve if you have a well detailed air barrier at the subfloor level, as 3/4" plywood subfloor is an acceptable thermal/ignition barrier. If you use this method, the only acceptable way to condition the crawl space (per code) is to dehumidify it. None of the ones that use house air pathways would be OK.

    There are some foams (Dow Thermax) that have heavy foil facings and are tested themselves to meet the various requirements, and their use without additional thermal or ignition barriers is nearly unrestricted. You still need to read the ESR carefully, but most applications will be OK, and any method of conditioning the crawl will generally also be OK. The downside is that Thermax is expensive and hard to obtain in some areas. It is also a polyiso insulation, so it should not be continuously wet. But the inside of your conditioned crawlspace should never be wet anyhow.

    The other option is to sheathe the foam with drywall. If your crawl space is very dry, something like greenboard might be OK, but I would still probably spring for one of the mold-resistant drywall products. If there is any chance that the crawl will get wet (most do), I would use a fiberglass-faced product like Dens-Glass. Glue the foam to the wall and the drywall to the foam, and use just a few fasteners to hold everything in place while the glue dries.

    As a final note, the fussy details around the band joist can be done with spray foam that extends from the subfloor down to the top of the wall foam. This spray foam does not require the thermal/ignition barrier.

    Except in high-termite risk areas, of course.....

  2. m854 | | #2

    "HOW IS THIS AN EXCEPTION IF YOU MUST USE R316.6 for Specific approval?"

    The exception is that you can use an ignition barrier (like sheet metal) which is a lower requirement than a thermal barrier (like drywall). One of the nearby sections lists prescribed thermal and ignition barriers, but I don't know off the top of my head.

  3. ChrisInIllinois | | #3

    Thanks guys, that what I was thinking. I am trying to hammer out the details of my crawl encapsulation.

  4. Jon_R | | #4

    Both the dehumidifier and exhaust only ventilation seem to meet the requirements. The latter does not change the status from unvented (otherwise R408.3 with be self-inconsistent). Similar with attics.

    See R314.5.4 for prescriptive choices for ignition barriers.

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