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I live in the United States in the State of Idaho. I have done a DIY project some time ago and my research then (Fall 2016) indicated that holes going from the first floor directly into the crawl space do not have to be fire sealed.

Recently, I have been going around the house noting different things that could be improved (like getting tamper resistant outlets). What I see these days with regard to fire sealing crawlspace holes is a mixed bag. People on various forums state they need to be sealed, but I cannot find a code listed anywhere that says this. I can only find code and professional material stating that going up from the first floor has to be sealed.

If these holes from the bottom of the first floor into the crawlspace need to be sealed, could someone please provide that code?

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  • I take it the crawlspace does not contain any storage or equipment spaces?
    – ThreePhaseEel
    Commented Feb 27, 2022 at 2:09
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    It's permissible to do better than code. Code is a minimum. A tube of caulk or a can of foam is not all that expensive relative to the price of the house...
    – Ecnerwal
    Commented Feb 27, 2022 at 2:45
  • @ThreePhaseEel - Correct. There's just pex down there. And Cat-6A + coax that I ran. (EDIT: And sewage, and HVAC ducts.)
    – wswartzendruber
    Commented Feb 27, 2022 at 4:43

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Idaho residential building code is based on the International Residential Code (along with all other states except Wisconsin, Washington DC, Puerto Rico, Guam, and the U. S. Virgin Islands; Mexico also uses large parts of it). The 2020 Idaho Residential Code § R302 - Fire-Resistant Construction and § R408 - Under-Floor Space do not say that you need to seal the holes.

R302 - Fire-Resistant Construction

R302.10.1 - Insulation

The only place in the entire R302 that mentions crawl spaces explicitly is:

Insulating materials installed within [...] crawl spaces [...]. They shall exhibit a flame spread index not to exceed 25 and a smoke-developed index not to exceed 450 [...].

This doesn't say you need to seal the holes, only that material inside the crawlspace must meet the same fire requirements as other locations in the structure. (R316.5.4 also mentions this.)

R302.11 - Fireblocking

In combustible construction, fireblocking shall be provided to cut off both vertical and horizontal draft openings and to form an effective fire barrier between stories, and between a top story and the roof space.

A careful reading of the initial paragraph seems to exclude the crawl space (because it may not be counted as a "story"), but it is also possible to read "to cut off both vertical and horizontal draft openings" and "to form an effective fire barrier between stories" as independent clauses and therefore to require fireblocking. (I don't think I would read it this way, but it's possible that some people might.)

R408

R408.3

If your crawl space is unvented (i.e. no vents in the exterior walls), you must have some kind of opening(s) to allow conditioned air into the crawl space (either pulled through by an exhaust fan, or pushed in by an HVAC system, unless you have a dehumidifier in the crawl space. (FineHomeBuilding has some drawings here.)

R302.13

To complicate matters even more, The base International Residential Code has this section, entitled "Fire protection of floors". The Idaho version of the code deletes this section entirely. This section does not explicitly mention fireblocking, just that "penetrations or openings for ducts, vents, [etc.]" are allowed, but it does not say you need to seal around the thing that goes through the hole.

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