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Foam board vs osb

T

Trent Carter

Registered User
Joined
May 13, 2020
Messages
4
Location
Maumelle, AR
Builders are substituting insulating foam board for osb. I have them providing CS-WSP at the corners and then CS-PF at garages. However, they are not using a nailing pattern that seems sufficient. Plus studs are on 24" centers. Without any other bracing, is this up to code? Since it is not officially structural, can I require a nailing pattern similar to that required for fiberboard, 3" edge and 6" field?
 
If there is anything about the construction that requires OSB such as the code or the approved plans....substituting foam insulation would not be approved. Then there is the exterior cladding which might not be appropriate over foam insulation.
 
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2018 IRC R602.10 Wall Bracing

Buildings shall be braced in accordance with this section or, when applicable, Section R602.12. Where a building, or portion thereof, does not comply with one or more of the bracing requirements in this section, those portions shall be designed and constructed in accordance with Section R301.1.

Exception: APA Simplified Wall Bracing Method, SR-102 may be used as an alternate method of wall bracing subject to limitations in document.
 
I agree with ICE approval of the foam board would most likely require re-submittal documents that would require AHJ approval prior to installation.

LIB or DWB bracing methods could be an alternative to an OSB sheeting design. Note: Foam board with some sidings can give you a wavy wall. If I was a customer and had a house under contract, the switch in wall design may not be something I'd want. Gun nailing needs to be watched for over and under shot nails.

SFB is another option, requires a lot more nails, our framers hated it due to requiring additional framing material to meet the nailing patterns, may not work on 24-inch center studding, that would have to be checked out.
 
There are wall bracing methods that don't use structural sheathing, and were used by a lot of designers and builders for years. When OSB was cheap and plentiful, it became the preferred method in a lot of regions. Now, it feels like we may need to re-learn how to do it without the OSB. But no matter what method you choose, and whether it's prescriptive or engineered, following the details is critical, from the foundation to the roof.

Start with IRC 106.1.3, where they can be required to show you where the bracing is and what methods they will be using. Then it's just a matter of deciphering the requirements...good luck. CS-WSP would require a 6"/12" pattern, stud spacing is dependent on other factors, such as fastener size, stories, what story etc.

IMHO, the code jumped the shark with wall bracing, too many variables and options. I haven't seen a non-engineered design in years, and I don't want to.
 
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