Wall height and bracing requirements ?

[klmArchitect]

Hello,

I've designed a preliminary plan calling for 21' tall walls on 3 sides. Intuitively knowing standard 2X6's wouldn't span 21' I've used the iLevel software and am using 2X8 LSL studs. My concern is racking during wind and I was wondering up to what height is this wall bracing section of the code good for ...

http://publicecodes.citation.com/st/ny/st/b400v10/st_ny_st_b400v10_6_sec002_par023.htm?bu=NY-P-2010-999999

I was focusing on system '3' as it's pretty much what would be done anyway but this 21' foot thing has me on edge and I'm not certain this section of the code recognizes these heights. Any help would be appreciated.

 

[rktect 1]

Read 301.3

 

[FredK]

Here's the story:

R301.3 Story height.

Buildings constructed in accordance with these provisions shall be limited to story heights of not more than the following:

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

Exception: For wood framed wall buildings with bracing in accordance with Table R602.10.1, the wall stud clear height used to determine the maximum permitted story height may be increased to 12 feet 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 is increased by multiplying by a factor of 1.20. Wall studs are still subject to the requirements of this section.

And see this table:

TABLE R602.3(5) SIZE, HEIGHT AND SPACING OF WOOD STUDSa

a. Listed heights are distances between points of lateral support placed perpendicular to the plane of the wall. Increases in unsupported height are permitted where justified by analysis.

So I say you need it engineered.

 

[pwood]

fred,

he is a rdp! he should be able to do the analysis, at least in california if they are competent

 

[klmArchitect]

Much appreciated. I figured this went beyond the scope of the code. Looking towards prefab shear walls.

 

[brudgers]

Much appreciated. I figured this went beyond the scope of the code. Looking towards prefab shear walls.

You'll still need engineering to determine the design of the pre-fab walls.

But there's not that much unusual about the analysis - the shear at the foundation doesn't change just because there is an intermediate diaphragm.