Best Choice For Tall Stud Walls

[KootK]

I've got some 14' 2x6 exterior stud walls. My designer swears to me that they work as 2x6 stud grade @ 8" o/c. Assuming that to be true, and I'll check, is there a practical limit on stud height irrespective of capacity? Should we be using an engineered wood product simply because a straight 2x6 stud grade stud will be difficult to find etc?

Capacity aside, how tall is too tall for regular stud grade stud walls?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[dcarr82775]

I find at around 15ft the deflection on a 2x6 stud due to wind becomes problematic.

 

[XR250]

At 15 ft. it is about L/280 with the 30% serviceability reduction and 18 psf load.
We are allowed L/120, but I usually won't go below L/240. If it has brick, I usually won't go below L/360.

 

[dcarr82775]

Yep, you are allowed L/120 and the drywall inside will can crack long before that.

 

[manstrom]

Note that you can reduce components and cladding wind loads by 0.7 for calculating deflection. It's buried in a footnote in the IBC somewhere. There are a lot of little tricks in exterior stud design.

When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.

-R. Buckminster Fuller

 

[mike20793]

If it has brick, I limit my deflection to H/400 at 50 yr MRI or H/282 for 10 yr MRI. Note that 400*0.7 is about 282, which means the 0.7*wind load for deflection is reducing the MRI. For higher wind zones (hurricane regions) the component and cladding wind load should be multiplied by about 0.55 which gives about H/219. The details of this can be found in an AISC 1993 Journal article by Lawrence Griffis. For other types of cladding, I follow the deflection limits presented in his article and convert to 10 yr MRI.

 

[XR250]

@Dcarr. I don't use L/120 unless I have to try to make something existing squeak by. I have never seen drywall crack in any instance that I could relate to out-of-plane wall deflection.
You would not believe how many houses around here have 18 ft. tall great room walls that are framed out of 2x4's with a double horizontal plate at 9 ft.running about 20 ft. They can be easily shaken by hand but no drywall cracks exist.