IRC Table R602.3(5) vs. Table R602.3.1 on the max height and spacing of 2×4 bearing stud walls
I’m designing a monopitch (shed-roof) residential addition in CZ6. I’m looking into using 2×4 walls with exterior EPS. Design calls for a 10′ high wall on the tall side of the shed and just under 8′ on the short side. I’d like to maintain all stud spacing at 24″ OC. Table R602.3(5) seems to indicate I can do this, specifically calling out 2×4 studs at 24oc up to 10′ high between lateral supports. However, what about Table R602.3.1, “Maximum allowable length of wood wall studs exposed to wind speeds of 115mph or less?” This seems to limit 10′ 2x4s to 16oc or less spacing even for small buildings. The two tables seem in conflict, so I suspect I’m mis-applying them. Any insights? I’m in Exposure B, wind speed 115mph. Building width is 16 feet clearspan. Thanks!
ps snow load is 50psf
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I think you need to read it as "It can be done under some assumptions, but needs modification under these conditions" IE wind loads, snow loads, seismic loads, and all that.
A tall wall exposed to wind speeds of 115mph will impose significant loads throughout the building, in particular the ceiling and roof diaphragms as well as the connection point of framing to foundation. If not allowed by code, you could pay an engineer to help with design. Costs more up front but you may get what you want in the end.
Has that section been modified where you are? This is what I get when I look it up:
R602.3.1 Stud Size, Height and Spacing
The size, height and spacing of studs shall be in accordance with Table R602.3(5).
Utility grade studs shall not be spaced more than 16 inches (406 mm) on center, shall not support more than a roof and ceiling, and shall not exceed 8 feet (2438 mm) in height for exterior walls and load-bearing walls or 10 feet (3048 mm) for interior nonload-bearing walls.
Where snow loads are less than or equal to 25 pounds per square foot (1.2 kPa), and the ultimate design wind speed is less than or equal to 130 mph (58.1 m/s), 2-inch by 6-inch (38 mm by 140 mm) studs supporting a roof load with not more than 6 feet (1829 mm) of tributary length shall have a maximum height of 18 feet (5486 mm) where spaced at 16 inches (406 mm) on center, or 20 feet (6096 mm) where spaced at 12 inches (305 mm) on center. Studs shall be No. 2 grade lumber or better.
Exterior load-bearing studs not exceeding 12 feet (3658 mm) in height provided in accordance with Table R602.3(6). The minimum number of full-height studs adjacent to openings shall be in accordance with Section R602.7.5. The building shall be located in Exposure B, the roof live load shall not exceed 20 psf (0.96 kPa), and the ground snow load shall not exceed 30 psf (1.4 kPa). Studs and plates shall be No. 2 grade lumber or better.
That is what I see also for R602.3.1 (I should have clarified we're on 2018 here). The first reference goes to Table R602.3(5), which I read as allowing 2x4 10' bearing wall studs on 24" centers. Then, it gives exceptions under which the Table R602.3(5) guidelines must be modified. E.g. if you really want to use utility grade lumber, you have to go 16 OC, etc
After this section TABLE R602.3.1 appears, floating there with nothing referring to it. I mean that literally - I have yet to find any code text that refers to this table. On another bldg code forum I read someone who interpreted Table R602.3.1 as a list of what is possible when meeting the above exceptions, but that's not obvious to me.
Sorry if I'm dense about this one - I can usually wrap my head around the IRC but I'm having a hard time channeling my inner paralegal on this!
I can't find the table you refer to. All I get when I look it up is what I posted. Can you find a link?
It occurs to me that Table R602.3.1 is in itself one big exception to Table R602.3(5). But if true what an awkward layout - the very first line of the table would limit 10' 2x4 studs to 16 OC in all buildings, a contradiction of the earlier Table 602.3(5).
The only reference I can find to Table R602.3.1 is within changelogs comparing 2012 IRC to 2015 IRC. Table R602.3.1 was apparently included in 2012 IRC and deleted for 2015 IRC.
Our current NC 2018 adopted code is based on 2015 IRC, and does not include that table anywhere, only Table 602.3(5).
Ah, found it in the 2012 code:
Is your state still using the 2012 IRC?
I'm in Minnesota, where our 2020 state code adopts most of the 2018 IRC. Here's the link to R602.3
I looked through the 2012 version Chris D linked above, where one of the exceptions explicitly refers to this table as what you can do if you meet the exceptions. But in the later version of the code for my state, the table is still there, but nothing refers to it. The exceptions now refer to a different table, R602.3(6) "Alternate wood bearing stud size..." which seems to be a new addition.
R602.3(6) was added for the 2018 IRC. I remember this because I was just looking at some tallwall stuff the other week for a project I'm doing, and it's not in our (2015-based) NC code so I wanted to find when it was added.
Interesting that the R602.3.1 table is red in your Minnesota code on iccsafe. I'm not entirely sure what that denotes, maybe that it's slated for removal? I looked on up.codes, and it's included in the Minnesota code there as well, so they agree at least.....
I looked at the model 2018 IRC and some other states codes and they seem to have struck Table R602.3.1entirely. R602.3.1 is still a _section_ but has no table of it's own. I'll have to find out what the red text on iccsafe stands for.
The easiest way to resolve this is to speak to y0ur local inspector. They are who will be the ones interpreting it at some p0int anyway.
Just about the wisest advice always, but not always so easy in a larger city.
Yeah, that's one of the advantages of living in a smaller community. I've already been on the phone to out local planner this morning.
And here we have it... seems MN went out of their way to keep the confusing table in.