Drywall Sheathed I-Joists

[Gunnar Alquist]

I just inspected a new/replacement build. The previous home burned-down in our fires and this is the replacement. The sides (not the bottom edge though) of some of the I-joists in the foundation crawlspace area have been sheathed with gypsum drywall.

Most of the covered joists are flanking screened foundation vents and I suspect this is intended to protect these joists from fire entering the vents. The vents are screened rather than the baffle type that I have been seeing.


The drywall is kind of pink-colored (women would probably refer to it as "mauve") and the labeling indicates it is a fire-rated material.


Apparently, there is something new coming out in either the IRC or the California Residential Code (CA modifies the codes in order to address issues in CA). This is regarding fire spread, particularly in I-joists. Another inspector directed me to the APA site and SR-405G

More homework.

[Jerry Peck]

Some observations:

Fastener spacing does not appear to meet any of the requirements I have seen for gypsum board applications

Fire protection require mudded and taped joists (it doesn't have to look nice) unless backed by framing.

The bottoms of the joists are left unprotected.

[Gunnar Alquist]

Some observations:
Fastener spacing does not appear to meet any of the requirements I have seen for gypsum board applications

Jerry,

In the attached APA SR-405G document (p.6), the fastener spacing is noted, and it looks like you are correct, it probably does not meet requirements.


Fire protection require mudded and taped joists (it doesn't have to look nice) unless backed by framing.

According to SR-405-G, mud and tape not required (p.8)


The bottoms of the joists are left unprotected.

Also not required by that particular document (p.7).

I-Joists do ignite easily and burn merrily (and quickly). But, according to the APA SR-405G, crawlspaces are exempted. The one thing that I did notice is that these wrapped joists are not at all locations, just in line with screened foundation vent openings (except one).

My only guess is that since they were using screened rather than an approved ember resistant vent, this was an option. I know that there is some new stuff in the CRC that addresses ember-resistant vents (R337.6). WUI (at least in CA) requires some kind of approved vent, such as a baffled or automatically closing vent.

I really don't know if SR-405G is a suggestion or one approved method of making I-joists fire-resistant. It'll take me a while to sort this out.