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24" O.C vs 16" O.C exterior load bearing wall

atvjoel

Registered User
Joined
Aug 1, 2021
Messages
98
Location
Alaska
Am I correct when reading R602.3(5) that I can frame 24" o.c vs traditional 16" o.c?

Details;
Single story
Engineered trusses, but I am not reading if that makes a difference
2x6 walls
24 foot wide by 64 feet long duplex.

I am not doing it to skimp, I am in code climate and this is a plan because of thermal bridging, not the $400 in extra lumber. I plan on rigid spray foam.

I hear a lot of yes and know online which is having me doubting, but I read it right on R602 and looks like as long as you are not a set distance you are spanning then its ok.

Thanks in advance
 

RickAstoria

-------------------
Joined
Oct 17, 2009
Messages
532
Aside from the function/spatial requirements, you are not limited to the 2x4 or 2x6 stud dimensions but your top plates might need to be a little more stout if you are going to support multiple floors. The header functions in all purposes like a beam between the studs (which in all truth are tiny little "columns" or "posts" if you may. Keep in mind the load you are applying on the "bearing" header and the columns. Most likely, it's not the studs that will be the issue but the double-top plates of 2x4 or 2x6 will max out sooner in it's load but for up to 3 stories, it might not be that much of an issue unless you are using some unusual load but if you may, you can change from a double-top plate to a 4x6 or 2x6 to 6x6 header beam. You may yet still use a 2x4 or 2x6 on top if you want to be technically a double-top plate but that would be unnecessary. If I was designing a 2-3 story home with 24" o.c. then I would change the top header into a singular solid beam that would span farther. You mentioned thermal bridging so you would have to account for that where the roof, wall and ceiling joins. If you are platform wall framing, you have double top plating at each floor and each platform framed wall is one story tall and essentially stacked on top each other for multiple floors. In a balloon framed system, this may be different so you have to account for in some fashion in the structural design and but running 3 story structure on regular 2x4 or 2x6 stud walls at 24" o.c. would be sketchy, in my opinion but on a 1.5 story structure or a 2.5 story home.... not a big issue especially if the walls are just one to 1-1/2 story tall stud frame from middle floor up to about say 5 feet above the upper attic/loft floor line while the ground floor being a solid concrete/CMU or some other more "sustainable" floor system that is adequate for the load. In any case, there is a lot of options. Some options might need an engineering consultant but sometimes, it doesn't. I don't think 24" o.c. spacing should be a problem for a 1-1/2 (1.5) story home but when you add multiple stories, that can be a problem as the cumulative loading may exceed the load bearing capacity of the studs which can handle up to a certain amount of load (axial load capacity). Basically, you can compute that as you would any post or column. What you don't want to do is overload those little "columns" or they will start potentially splitting vertically.

24" o.c. isn't necessarily the problem. Depends on the load. If you have concentrated loads that needs to be supported, it might be on the weak side with regular nominal 2x4 or 2x6 studs.

The header should span but I would probably beef it up to a single 4x4 or 4x6 ( with grains flat in the best orientation for use as a beam ). If your wall is a 2x6 wall, the 4x6 should be flat so the. The extra 1/2" of vertical depth would be adding a little more load carry capacity to span 24" but you could go to 6x6 if you feel more comfortable with spanning 24". If you're wall is 2x4 walls then 4x6 on edge (with grains flat in the best orientation for use as a beam) would be more than adequate but you'll need to plan out right where the header will be before the sill plate of the next wall up (assuming you're using conventional platform framing) to address thermal bridging. In cold environments, I might actually go to 2x8s as studs because it provides a deeper wall cavity for more insulation value.
 

Joe.B

Registered User
Joined
Dec 4, 2020
Messages
555
Location
Myrtletown Ca
The question I would pose first is are you designing this based off of prescriptive design requirements from the IRC, or are you employing an Architect and/or Engineer to provide an engineered design?
 

RickAstoria

-------------------
Joined
Oct 17, 2009
Messages
532
The question I would pose first is are you designing this based off of prescriptive design requirements from the IRC, or are you employing an Architect and/or Engineer to provide an engineered design?
IIRC about Alaska laws regarding architectural/engineering title, practice, and licensing requirements, non-prescriptive elements would be something that may require an engineer. The building code may require it but this depends on a lot a factors of the design not just what was stated in the original post.
 

Beniah Naylor

Sawhorse
Joined
Sep 10, 2020
Messages
311
Location
Manhattan, Kansas
Check out the this video from APA, it's all about framing with 2x6s on 24" centers. This is the YouTube link, but you can get to it from the APA website and get ICC CEU hours by watching it there. This video explains way more detail than we can in a forum like this.

APA Advanced Framing

Also, consider adding continuous insulation on the outside of the studs. If done properly, it makes a huge difference on the energy side.
 

fatboy

Administrator
Joined
Oct 17, 2009
Messages
6,570
Location
Northern CO
R602.3.2 Top plate. Wood stud walls shall be capped with
a double top plate installed to provide overlapping at corners
and intersections with bearing partitions. End joints in
top plates shall be offset not less than 24 inches (610 mm).
Joints in plates need not occur over studs. Plates shall be not
less than 2-inches (51 mm) nominal thickness and have a
width not less than the width of the studs.

Exception: A single top plate used as an alternative to
a double top plate shall comply with the following:
1. The single top plate shall be tied at corners, intersecting
walls, and at in-line splices in straight
wall lines in accordance with Table R602.3.2.
2. The rafters or joists shall be centered over the studs
with a tolerance of not more than 1 inch (25 mm).
3. Omission of the top plate is permitted over headers
where the headers are adequately tied to adjacent
wall sections in accordance with Table R602.3.2.

R602.3.3 Bearing studs. Where joists, trusses or rafters
are spaced more than 16 inches (406 mm) on center and
the bearing studs below are spaced 24 inches (610 mm) on
center, such members shall bear within 5 inches (127 mm)
of the studs beneath.
Exceptions:
1. The top plates are two 2-inch by 6-inch (38 mm
by 140 mm) or two 3-inch by 4-inch (64 mm by
89 mm) members.
2. A third top plate is installed.
3. Solid blocking equal in size to the studs is
installed to reinforce the double top plate.
 
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