IRC Wood Stud Wall Interpretation

[CBSE]

This seams like a silly question, but I'm trying to interpret the IRC...never done that before. Attached is a pdf of the wall stud heights for prescriptive design. Under footnote "B", one of the exclusions says that the table is only good if the maximum span for floors and roofs does not exceed 12 feet. Am I to interpret that for anything to be prescriptive path, wall studs cannot have more than 6feet of tributary area on them?

Clarification: I'm not designing a system, I'm answering a question that has been asked for my opinion.

 

[XR250]

I never use that table as it requires studs with E = 1.6x10^6 (or SYP in our area). Everybody uses SPF which has E = 1.4x10^6.
Make yourself a spreadsheet and be done.

 

[mike20793]

I think you are interpreting it correctly. If you engineer it, it likely would be able to take more tributary width, which is pretty easy to do with a spreadsheet as XR250 suggested.

 

[CBSE]

I'm not engineering based on the table. I was just seeing what others interpretations were of the table. I see a lot of houses built in my area that are drawn by residential drafters and the question of what my interpretation is of the table was asked. It really surprised me when I saw the 12ft span requirement.

 

[medeek]

I just use my wall stud spreadsheet. The only prescriptive tables I use with any frequency is the AWC tables for deck joists.

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

 

[CBSE]

I use my spreadsheets and woodworks as well. Just trying to give an interpretation to a friend...and I have never really looked at the IRC or even tried to interpret prescriptive path.

 

[dhengr]

CBSE:
The IRC is a conservative prescriptive code, devised by committee, for any DIY’er or builder to follow to the letter, without the need for any real serious engineering involvement on the design. It is intended to keep these nail benders out of trouble, for the most part, if they read every sentence and every footnote (do they ever?) and follow it explicitly. And, of course, it is not written with clarity of engineering thought in mind; rather it is written to keep some dumb fools from hurting others, in their building efforts, hold them back from the upper limits, and also to CYA (to cover their ...) from the committee standpoint. Even the people on the committees can’t explain it in detail, give a detailed derivation of some of the tables, etc., or give a comprehensive history of the development and progression of some of the thinking which went into its birthing and re-birthing. In the GOOD OLD DAYS a good engineer with a reasonably current Ed. of the NDS could pretty well work his way through those tables and explain their general derivation, meaning and intent. But today, with the rate of change of the NDS, lumber stress grades, load and stress factors (+ & -), various other adjustment factors, wind speed maps and codes and stds. in general, it is tough to know which version of each code or std. was applied to that particular table, or what revision of that table you are looking at. Then, you have the committee issue itself where simple Engineering Mechanics and Strength of Materials, a much less convoluted and more readable NDS and good sound engineering judgement and common sense are many times subverted by one hundred individual opinions, experiences and likes or don’t likes, and of course the majority rules, everyone has a right to an opinion and a vote, right or wrong, clear or not, and the picture and derivation becomes much less clear.

In looking at the table, you can see that for a constant max. vert. loading (12', committee’s choice) on the wall, the stud size increases and/or the spacing goes down, as the stud length gets longer. That’s common sense, they’ll grasp that. The committee stopped at 2x6 studs because wider studs start needing some special engineering attention given the loads they’ll carry as a beam/column. If you understood exactly how that table way developed and formulated, you could undoubtedly develop a table for 14' or 16' roof and fl. spans, a new max. vert. load, added to the stud bending action. Throw in some ‘tall wall’ design and thinking, consider that these longer exterior studs are more bending member than bearing (just compression) member. And, you have a reasonable first cut at how you would develop a table like that. Then, you start looking at the interaction formula for a 2x4 or 2x6 and see how far you can push a given length for variations on bending and axial load.

My explanation of the table would be to reiterate some of the above, and add that I can often save them money/time/matr’ls., and clean up their design and details by designing it to the IBC, they can’t without involving me.

 

[CBSE]

dhengr: Thanks for the comments. And yes, I don't get caught up in the IRC and understanding it.

You make a very good comment at the end, and it is a comment I have said to many drafters looking to get bits and pieces of their homes engineered. It always surprises me how owners get so upset for having to pay for engineering fees. It just baffles me.

 

[XR250]

Does anyone frame walls with material that has an E of 1.6?
Just curious of what gets used in other areas.

 

[boo1]

2x4 and 2x6 SYP are not stable and warp. I have use 2x8 SYP in tall walls.

 

[XR250]

2x4 and 2x6 SYP are not stable and warp

Exactly. No one uses them but we are stuck with a table designed around them.