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Stud Height?

Sifu

Sifu

SAWHORSE
Joined
Sep 3, 2011
Messages
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Any opinions on the difference between tables R602.3(5) and R602.3.1?(2009 IRC) The former limits laterally unsupported stud heights to 10' under any and all conditions for bearing studs. The latter seems to contradict this, given lesser wind zones/seismic zones/snow loads etc. and differing conditions for what size they are and what they support and the spacing used. I know contradictions are unheard of in the codes! Just looking for discussion and what others are permitting.
 
You need to look at the footnotes in Table R602.3.1. The use of this table is limited to tributary loads not exceeding 6 feet and spans not exceeding 12 feet and specific grade of lumber and snow loads. Where in Table R602.3(5) you are not limited to that specific criteria. Table R602.3.1 is pretty limited.
 
I have read the 301 "irregular structures portion" as it pertains to story height and stud height. I also referred to the associated CH6 portions.

This was a full on exercise in brain damage.

I would recommend having 2 code books so you can read on and open the other to the part that is being referred to.

I did this, and took notes to figure it out.

We are Seismic D1 and my best determination is that you can have a 10 foot stud height prescriptively. Above that, you need to get an LDP approval.

( I could be wrong, but I think that is correct).

Have a few beers before you try reading the sections. ( I can tell the people that wrote them did).
 
In accordance with R301.3 you can actually increase stud height to 12 feet without a design if you increase the amount of bracing by 10% in wind and 20% in seismic. This allows you to increase the 10 foot stud height in TABLE R602.3(5) to 12 feet.

1. For wood wall framing, the laterally unsupported bearing wall stud height permitted byTable R602.3(5) plus a height of floor framing not to exceed 16 inches (406 mm).

Exception: For wood framed wall buildings with bracing in accordance with Tables R602.10.1.2(1) and R602.10.1.2(2), the wall stud clear height used to determine the maximumpermitted story height may be increased to 12 feet (3658 mm) without requiring an engineered design for the building wind and seismic force resisting systems provided that the length of bracing required by Table R602.10.1.2(1) is increased by multiplying by a factor of 1.10 and the length of bracing required by Table R602.10.1.2(2) is increased by multiplying by a factor of 1.20. Wall studs are still subject to the requirements of this section.

TABLE R602.3.1 permits you to increase stud heights within the parameters of the footnotes of the table below, which is pretty limited:

a. Design required.

b. Applicability of this table assumes the following: Snow load not exceeding 25 psf, fb not less than 1310 psi determined by multiplying the AF&PA NDS tabular base design value by the repetitive use factor, and by the size factor for all species except southern pine, E not less than 1.6 × 106 psi, tributary dimensions for floors and roofs not exceeding 6 feet, maximumspan for floors and roof not exceeding 12 feet, eaves not over 2 feet in dimension and exterior sheathing. Where the conditions are not within these parameters, design is required.

c. Utility, standard, stud and No. 3 grade lumber of any species are not permitted.
 
What confused me or led me back to the 10 foot conclusion was the text later in 301.3 that says

"An engineered design

shall be provided for the wall or wall framing members when

they exceed the limits of Chapter 6.

It appears they have taken a very simple issue and confused it to the point that even those who work in the codes every day have trouble deciphering it.

I guess i defaulted to the requirement that if a conflict exists, the more restrictive would govern, in this case, studs exceeding 10 feet require design.
 
I am sticking with the 10' rule as a baseline. The problem is a lot of neighboring jurisdictions seem to have come up with some ideas of there own. One of them says any wall over 10' should be 2x6. Most others don't seem to get too involved with it. Interestingly I went out on one a few days ago and one of the deficiencies was a 16' wall, balloon framed, with 9 windows (& 9 headers!). In the entire 18' wide wall there were only 6 uncut studs, 3 on each end. When I very, very gently grabbed a stud to demonstrate to the framer why he couldn't do this the wall deflected in and out about 3". So much so the framer actually retreated from the wall for fear it was going to come down.

Now for the next question:

Given a 16' tall wall, framed with 8' foot studs and a double top plate, then another 8' stud wall framed on top of it would that meet the code? This builder did that at the next house and the wall was a little stiffer but not much. The way I see it, he didn't exceed the 10' stud height, he simply stack framed. Do the properly installed wall plates constitute "lateral supprort"? The DP I required for the first wall didn't seem to think so but I'm not so sure.
 
Just read the WFCM. It says studs are limited to 10' between horizontal supports. So again, are the plates considered the horizontal supports. I have posed this question to a state division of engineering so I'll see what their opinion is.
 
So again, are the plates considered the horizontal supports
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No they are supporting the verticle loads from above. Horizontal supports will resist lateral movement in the wall. Stacked walls create a "hinge" point and a very weak at resisting lateral movement.
 
Robert S said:
In the entire 18' wide wall there were only 6 uncut studs, 3 on each end........with 9 windows (& 9 headers!).
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What about king studs at the nine headers?
 
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To muddy the water even more, what about non bearing walls. Table 602.3(5) allows for taller studs when the wall is non bearing. So let's say the building has a 2 story foyer that is 8' wide and the designer puts a beam across the exterior wall of the foyer, would that make the 18' wall studs non bearing and compliant?
 
ssteen said:
To muddy the water even more, what about non bearing walls. Table 602.3(5) allows for taller studs when the wall is non bearing. So let's say the building has a 2 story foyer that is 8' wide and the designer puts a beam across the exterior wall of the foyer, would that make the 18' wall studs non bearing and compliant?
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Maybe?...What holds the beam up?

I agree w/ MT on the lateral support.....it needs to be a floor ceiling/ system or engineered....
 
Got word back from the engineers, plates do not mean "lateral support". Also, the hinge effect makes platform framing a no go as well. They directed me to a good article in JLC on tall walls that puts it easily understood terms.
 
The beam is being held up buy the normal height exterior walls that are adjacent to the 2 story foyer. How about a gable end wall on a 2 story room, such as a great room.
 
Platform framing implies (and only works BTW when) there is a 'platform' in between the stacked walls. That platform becomes the base for the rigid diaphragm that resists, among other forces, lateral loads.
 
How about a gable end wall on a 2 story room, such as a great room.
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The designer/contractors need to think outside the box in these situations

I have a 40' long 20' high gable end wall in my house with 4 6/0 x 5/0 windows. It is 2x6 ballooned framed @ 12" OC and the only way to reduce the deflection and meet the lateral wind loads (90mph) was to build a 12" wide x 8" high box beam shelve on the inside of the wall with 2 12" I-joist laid horizontally. The i-joist was the only light weight material that came in a continuous 40 ft length. There is zero deflection in that wall.

I could have used some steel columns within the walls but at the time I built steel prices where out of sight.
 
I have built similar box beam shelves, though not quite as big, in two story great rooms (in my past life), of course the homeowners just thought I was giving them a nice plant ledge. I never told them it was under the instruction of the DP. I just took all the credit for being so artsy.

JBI is correct about platform framing, and confirmed by state PE, I was just looking for a clearer meaning on "laterally supported"...and now I think I have it.
 
bearing walls over 10' are outside the scope of the prescriptive code.. hire an engineer .. see R301.1.3 - Engineered design is required when "a building of otherwise conventional construction contains structural elements exceeding the limitss of Section R301 or otherwise not conforming to this code".
 
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during construction I think about it turned on its side, as a floor, the wind is providing the live load. The "plant shelf" is a girder. The ends of the girder need sturdy support down to the foundation. In this case the beam needs to be well connected to the walls and the walls need to be able to carry that reaction to the foundation. My plant shelf on the current job is the porch roof.

MT, I know what you meant but the zero deflection comment sparked a memory. When asked I made the mistake of telling the sawdoc that the rail on the mill was perfectly straight and level. He told me to go back and measure better :) .
 
peach said:
bearing walls over 10' are outside the scope of the prescriptive code.. hire an engineer .. see R301.1.3 - Engineered design is required when "a building of otherwise conventional construction contains structural elements exceeding the limitss of Section R301 or otherwise not conforming to this code".
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I believe you can increase stud height (prescriptively) under certain conditions. (2009 IRC)

1. Section R301.3, Exception to Item 1

2. Table R602.3.1
 
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