Wall height question IRC 2018

[Dan_Shade]

Not a timber frame question, but I didn't know where to post...

I'm building a 32x64 building and have confused myself reading the code requirements.

I want to put a 12' tall 2x6 wall (sheathed in 7/16 osb) on top of a 20" tall block wall.  Some areas of the code look like its ok, other areas say max stud length for load bearing wall is 10'.  I'm looking at R602.3(5) and R602.3(6)

[Don P]

I'm betting that we are not talking about a residence, that is the prescriptive residential code for habitable buildings. Correctly you would probably be in the construction code. But let's see if you can get there prescriptively.

It does look like that section has been rewritten, somewhere in the footnotes it used to limit those tables to 12' wide building sections, effectively useless. I'm seeing a remnant in R602.3.1 exception 2, however, reading exception 3 should get you there.

[Dan_Shade]

The building will not be a residence. 

County inspectors use irc 2018.

I'll give them a call to make sure I'm on the correct path. 

Thanks 

[Don P]

I doubt it'll go there but just in case as a note for later cause I'll forget this path.
Curiosity got me, and I had both codes open on the computer. The table in the construction code looked the same as in the residential code. I then looked in the code referenced WFCM, Wood Frame Construction Manual and again bumped into the 10' prescriptive max height. Looking for the reasoning I opened up the commentary to the prescriptive section of the WFCM (these are I think also downloads at awc.org) Starting on pg 113 is a design procedure if needed (with examples, woohoo!). Basically take the tributary area of a stud, calculate and apply the design wind load, check bending and deflection at that stud length.

*Referenced Standards are part of the code... diving deeper than most inspectors have been, go to chapter 44 of the IRC "Referenced Standards" scroll down to AWC (American Wood Council) click on that and among other titles the WFCM will show up there. This is the kind of path to show an inspector when, although what you might be proposing is not in a prescriptive table, it is designed according to "accepted practice" through the use of a recognized referenced standard. 

The next question to run down is about the 20" tall block wall that is laterally unsupported at the top, there's always something.

[Dan_Shade]

Out of curiosity, how is a block wall typically laterally supported? 

[Don P]

Typical lateral support is at the bottom by a slab and the top by a floor. Here there is an unsupported top edge that the wall is sitting on top of. Good for water, bad for stability. 


Probably start here with concrete stem walls to get some context;
R404.1.3.2.2 Concrete foundation stem walls supporting light-frame above-grade walls.

Concrete foundation stem walls that support light-frame above-grade walls shall be designed and constructed in accordance with this section.

• 1.Stem walls not laterally supported at top. Concrete stem walls that are not monolithic with slabs-on-ground or are not otherwise laterally supported by slabs-on-ground and retain 48 inches (1219 mm) or less of unbalanced fill, measured from the top of the wall, shall be constructed in accordance with Section R404.1.3. Foundation stem walls that retain more than 48 inches (1219 mm) of unbalanced fill, measured from the top of the wall, shall be designed in accordance with Sections R404.1.1 and R404.4.
• 2.Stem walls laterally supported at top. Concrete stem walls that are monolithic with slabs-on-ground or are otherwise laterally supported by slabs-on-ground shall be constructed in accordance with Section R404.1.3. Where the unbalanced backfill retained by the stem wall is greater than 48 inches (1219 mm), the connection between the stem wall and the slab-on-ground, and the portion of the slab-on-ground providing lateral support for the wall, shall be designed in accordance with PCA 100 or in accordance with accepted engineering practice.

Then masonry stem walls;[/list]
R404.1.4.1 Masonry foundation walls.

In buildings assigned to Seismic Design Category D₀, D₁ or D₂, as established in Table R301.2, masonry foundation walls shall comply with this section. In addition to the requirements of Table R404.1.1(1), plain masonry foundation walls shall comply with the following:

• 1.Wall height shall not exceed 8 feet (2438 mm).
• 2.Unbalanced backfill height shall not exceed 4 feet (1219 mm).
• 3.Minimum nominal thickness for plain masonry foundation walls shall be 8 inches (203 mm).
• 4.Masonry stem walls shall have a minimum vertical reinforcement of one No. 4 (No. 13) bar located not greater than 4 feet (1219 mm) on center in grouted cells. Vertical reinforcement shall be tied to the horizontal reinforcement in the footings.

Foundation walls, supporting more than 4 feet (1219 mm) of unbalanced backfill or exceeding 8 feet (2438 mm) in height shall be constructed in accordance with Table R404.1.1(2), R404.1.1(3) or R404.1.1(4). Masonry foundation walls shall have two No. 4 (No. 13) horizontal bars located in the upper 12 inches (305 mm) of the wall.