Raising Roof on Existing Wood frame building

[TFreeman]

We have a client looking at using an existing 50 ft x 215 ft wood building as an assembly shop. The walls are 2x6 @ 16" and the roof are trusses @2' o/c. The current eave height is approx. 12'. The client would like to raise the eave to 24'.

A quick check of the code says he needs 2x10 walls minimum.

So a couple questions :

Can the wall be stepped, i.e. 2x10 to 12' and 2x6 above?

The code considers the wall studs pinned at each end. Can tie anchors such as the Simpsons products be used to provide a fixed end conditions for design purposes?

Can the same type of Simpson products be used to provide a moment connection at a stud splice?

I have my own opinions on these but a searching for some other perspectives.

thanks

 

[Zulak]

Designing wood with fixed ends doesn't seem practical, and the splice from a 2x6 to a 2x10 also seems ugly. New studs, full height is the way to go, or try a small steel frame inboard of the existing wall with a horizontal girt at the 12' elevation (saving the lower 2x6 wall). Don't allow owners with tight wallets to compromise your engineering judgement.

 

[redhead]

Think of the wall studs as if they were floor joists, because the determining factor is their ability to resist the wind as bending members as well as acting as compression members. I think you would be uncomfortable walking on floor joists spanning 24 feet if they suddenly changed from 2x10 to 2x6 in the middle of the span.

Also, I know of no effective way of introducing a moment type connection into the base of the wall with Simpson connectors. You can reduce the overall unbraced length of the studs by introducing knee braces at the top of the wall.

 

[TFreeman]

Thanks Folks,

Just what i expected to hear. But I had to check these off my list of ideas.

 

[Trussdoc]

You could try attaching a cold-formed steel stud the full height of the wall, and use a 2 x 6 at the top; for design, you may consider the combination as a composite member, or else let the steel stud do all the work, with the wood acting only as a nailer for the sheathing.

You can't get a complete moment connection at the base, so I usually use (wl^2)/9 to compute moment due to wind lateral loading.