Interpretation #: ALB-2023-38 [2020 IRC-R302.6]

Building or Fire Safety Law Interpreted

(675 IAC 14-4.4) 2020 Indiana Residential Code, Section R302.6 Dwelling-garage fire separation. The garage shall be separated as required by Table R302.6. Openings in garage walls shall comply with Section R302.5. Attachment of gypsum board shall comply with Table R702.3.5. The wall separation provisions of Table R302.6 shall not apply to garage walls that are perpendicular to the adjacent dwelling unit wall.

• At separation between garage and the residence and attics: Not less than 1/2-inch gypsum board or equivalent applied to the garage side.

• At separation between garage and habitable rooms above the garage: Not less than 5/8-inch Type X gypsum board or equivalent.

• At structure(s) supporting floor/ceiling assemblies used for separation required by this section: Not less than 1/2-inch gypsum board or equivalent.

• At garages located less than 3 feet from a dwelling unit on the same lot: Not less than 1/2-inch gypsum board or equivalent applied to the interior side of exterior walls that are within this area.

Issue

Does Section R302.6 of the 2020 Indiana Residential Code (IRC) allow the use of 7/16-inch oriented strand board (OSB) in place of 1/2-inch gypsum board in the assemblies separating the garage from the dwelling?

Interpretation of the State Building Commissioner

Section R302.6 of the 2020 IRC neither directly allows nor directly prohibits the use of 7/16-inch OSB in place of 1/2-inch gypsum board in the assemblies separating the garage from the dwelling, but instead vests authority in the local building official to approve its use as an equivalent material or product.

Rationale

Section R302.6 of the 2020 IRC states that the assembly or assemblies separating the garage from the dwelling must comply with the requirements of Table R302.6. This table states that the separation between the garage and the dwelling must be 1/2-inch gypsum board "or equivalent," and between the garage and any habitable rooms over the garage it must be 5/8-inch gypsum board "or equivalent."

The inclusion of the phrase "or equivalent" – in both sections – is clear indication that gypsum board of the specified thicknesses, installed in accordance with Section R702.3.5, is not the only possible acceptable option. However, while "equivalent" is not a code-defined term, implicit in its use is the concept that some entity must determine whether the performance qualities of the proposed material or product meet the standards established by the originally named material or product – and vest formal approval authority, as appropriate, for the use of the proposed material or product. That determination must lie with the building official. To place it in the hands of the designer or building owner would be the functional equivalent of making the design and construction industry self-regulating.

"Building official," unlike "equivalent," is a code-defined term, meaning the local official or officials in the project's jurisdiction. They are the party responsible for determining the acceptability under the code of any material or product proposed as the "equivalent" of the code-named material or product.¹

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¹ See Section 106 of the 2020 IRC for a discussion of the evaluation process for proposed alternate materials, methods, and equipment – including required evidence and applicable testing and standards.