Attic Service Flooring

[aaronm]

Code Man:

Given a residential attic service floor constructed under the 2012 IRC, the builder used 7/16" OSB panels for flooring atop 2X8 SYP ceiling joists spaced 24 inches on center. Can you please direct me to the specifications, be they IRC, APA, or whatever, that state what is required?

Thanks,

[Jerry Peck - Codeman]

Aaron, presuming 2012 construction was under the 2009 edition of the IRC, start at M3105.1.3 Appliances in attics, which states within that section "The passageway shall have continuouse solid flooring in accordance with Chapter 5 not less that 24 inches (610 mm) wide."

Chapter 5, states "R502.2 Design and construction. Floors shall be designed and constructed in accordance with the provisions of this chapter, Figure R502.2 and Sections R317 and R318 or in accordance with AF&PA/NDS.", keep in mind that there is an "and" and an "or" in the above (see underlining and bold, which are mine).

The attic service "floor" is required to meet the same requirements as other "floors".

[aaronm]

Aaron, presuming 2012 construction was under the 2009 edition of the IRC, start at M3105.1.3 Appliances in attics, which states within that section "The passageway shall have continuouse solid flooring in accordance with Chapter 5 not less that 24 inches (610 mm) wide."

Chapter 5, states "R502.2 Design and construction. Floors shall be designed and constructed in accordance with the provisions of this chapter, Figure R502.2 and Sections R317 and R318 or in accordance with AF&PA/NDS.", keep in mind that there is an "and" and an "or" in the above (see underlining and bold, which are mine).

The attic service "floor" is required to meet the same requirements as other "floors".

The adopted code was the 2012 IRC. I was going to cite APA's Floor Construction Table 15, which appears to require 23/32" OSB. Delving too deeply into the NDS induces a sort of mind haze that persists for days.

[Jerry Peck - Codeman]

I noticed a typo of mine in your quote of my answer: M3105.1.3 should have been M1305.1.3. My typo and error for not catching it on my re-reading of it.

That said, the 2012 IRC M1305.1.3 states the same thing as the 2009 IRC.

Now (still in the 2012 IRC) let's go to:

R503.2 Wood structural panel sheathing.
- R503.2.1.1 Subfloor and combined subfloor underlayment
- - Where used as subflooring or combination subfloor underlayment, wood structural panels shall be of one of the grade specified in Table R503.2.1.1(1). When sanded plywood is used as combination subfloor, the grade, bond classification, and Performance Category shall be as specified in Table R503.2.1.1(2).
- - - Table R503.2.1.1(1) Allowable Spans and Loads for Wood Structural Panels for Roof and Subfloor Sheathing and Combination Subfloor Underlayment a, b, c (see notes a, b, c)

Note that note c states: "Applies to panels 24 inches or wider.", this is something that many forget when using structural panels from the Table. If the structural panel is less than 24 inches wide, then the table does not apply. Given that M1305.1.3 requires a floor "not less that 24 inches (610 mm) wide", less that 24 inches wide is not a concern ... I presume.

Table R503.2.1.1(1) Live Load (see notes h, i). Then, when the structural panel is used as a single floor, i.e., as for a service floor in an attic, go down the Underlayment, C-C plugged, single floor (see note e), I presume that the floor is on the truss bottom chords and that the trusses are at 24" o.c., which requires a minimum of 23/32, 3/4 for the structural panel for a single floor.

[aaronm]

Thanks JP