Structural Engineer - 15' dimensional lumber question

[jburban]

Hi,
New poster here....
Working on a garage 28x40 with 15 foot ceiling. Blueprints call for a 4 foot CMU wall with 11 foot 2x6 on top - to get 15'. Code states dimensional lumber height limit of 12 feet - unless a structural engineer can certify it meets the wind/bracing specs etc. Structural engineer I originally used for the 4' cmu, 11' lumber work-up says can't be done. Going to try and find a second opinion but curious if anyone has succeeded in a similar build with 2x6 or even 2x8 at full 15 foot?
Thanks, H

 

[loganb]

You're already employing the services of a licensed professional familiar with local codes and interpretation of said code....so you're going out to the wild untamed masses who have no idea of location, site specific wind speeds, topographic factors or design loads to be considered and expect what....?

If the local engineer say 15' can't be done with dimensional lumber, instead of paying for a 2nd opinion to likely get the same answer.....ask how else you could get there without the CMU wall? Light gauge metal framing, replacing 2x lumber with LVL/LSL, tilt up precast concrete(a constraint of it being cheaper then drawn system was not listed)...

 

[strutaeng]

15' tall wall? 2x6s should work.

My house has a portion I added with a double volume space and I used 2x6 @ 16" o.c: 8' ceiling + 1' floor + 8' ceiling of second floor = about 17'.

I worked on this cool commercial project once. One story, but had like 20' tall walls. That one required deep studs. IIRC we specified 2x8s and 2x10s.

Maybe you in a coastal region with higher wind speeds?

 

[Firebrick43]

Does the CMU wall have vertical cells filled with rebar and bond beams/rebar?

 

[u2slow]

I have a 16' wall (20' wide) on the gable end. Needed to be 2x8" studs 12" oc; and two spots had 6 sistered together. I needed a $500 engineers stamp for that.

 

[jburban]

yes, filled CMU. The 12' limit is stipulated in the VA residential wall bracing code - so I think it's a statewide thing. Even a 2x8 structure would be cheaper than a 4' wall of CMU or formed concrete. Anyway, mostly curious if others encountered this and successfully showed a structural engineer solution to all wood construction of 2x. Thanks H

 

[Sumboodie]

14ft 2x6 walls on my place. 2ft OC. Held up fine to 7.2 earthquake and near 100mph winds.

 

[bluedog225]

Engineers are interesting folk. I don’t doubt he’s right.

But if you ask if there is another material that would work, he might say “sure, LVL or timberstrand or some other engineered product.“. Or maybe if you cover it with 3/4 ply.

I’ve got 20’ walls from my injuneer.

 

[loganb]

Engineers are interesting folk. I don’t doubt he’s right.

But if you ask if there is another material that would work, he might say “sure, LVL or timberstrand or some other engineered product.“. Or maybe if you cover it with 3/4 ply.

I’ve got 20’ walls from my injuneer.

Goodness.....is that doubled up 1-3/4 x 5-1/2" LSL or 7-1/4" deep?

 

[RivennHewn]

Having a tall wall as a component of a structure is different than having 4 tall exterior walls and no interior walls.

 

[carlaisle]

There are a lot of details missing here. A different engineer is not going to give you a materially different answer unless you ask a different question. Try asking the engineer who is already familiar with your project how you can get your 15' finished height with dimensional lumber. Since the original plan called for 2x6 construction, he may have said no under the assumption you wanted to built a 15' tall wall out of standard 2x6s. What if you used 2x8s or 2x10s? What bracing/sheathing would be required to make that system acceptable? Explain that you are trying to avoid the masonry crutch. Engineers are problem solvers, but you need to be very clear about the design constraints before they can provide a solution that meets all of the engineering requirements and your design requirements.

 

[bluedog225]

Goodness.....is that doubled up 1-3/4 x 5-1/2" LSL or 7-1/4" deep?

From memory it’s doubled 2x6 timberstrand on 12” centers with 3/4 ply. Nice and straight.

 

[Firebrick43]

There are a lot of details missing here. A different engineer is not going to give you a materially different answer unless you ask a different question. Try asking the engineer who is already familiar with your project how you can get your 15' finished height with dimensional lumber. Since the original plan called for 2x6 construction, he may have said no under the assumption you wanted to built a 15' tall wall out of standard 2x6s. What if you used 2x8s or 2x10s? What bracing/sheathing would be required to make that system acceptable? Explain that you are trying to avoid the masonry crutch. Engineers are problem solvers, but you need to be very clear about the design constraints before they can provide a solution that meets all of the engineering requirements and your design requirements.

I was thinking along these lines. One serious issue I see is the 28’ wide. If you have a garage door in that end wall that is wide and tall, say 16’x14’ it could very hard to have enough wall left to create a diaphragm with what is lesft of the wall. Even worse is both end walls . Foor config is very important to know in this situation!

So is wall/roof deck to be sheathed in ply/osb or not?

 

[treehick]

When I used to work on a post-frame crew, we'd do all sorts of different heights with laminated posts, 8' oc, with trusses attached on them. I'm not sure what the tallest was, but it was a grain elevator shed with only 2 "solid" walls and 2 "door" walls - and they were laminated posts from the ground up.

Otherwise, I don't think I've heard a requirement of block first and then framing. But maybe that's a local code issue.

 

[billconner]

Please clarify: 4' block plus 11' stud was OK with engineer but 15' stud is not? That is basic IRC.

Carlaisle has your best answer.

I did block stem wall (with surface bond cement) with 2x6 stud wall atop it. Very simple.

 

[jar944]

Lots of homes around here with 18-25' stick framed walls, though it's not usually the entire house, and doesn't have large holes in the field for cars to pass through.

 

[FredWanaker]

The real question the OP really asked is how do I avoid the cost the engineer designed into the plans. He is objecting to the CMU wall because of the cost. The question he needs to ask the engineer is "How do I reduce the cost of materials in building this garage?" Frankly it is a good question but he needs to be careful that he doesn't throw more money at solving the problem then it would have cost him to just follow the original plans. I worked a mason in High School so many years ago. Building walls is not all that hard, just tedious to get it right.

 

[vavet]

My detached garage was built in 2017, so it's been a few years, but I remember a similar conversation with my GC, although not to get the 15 foot. I wanted 12-1/2 foot. We were trying to avoid using 2x6 lumber, so we used a stem wall, and built the 8' 2x4 wall on top of that, and then used a ceiling truss that angled up from the side to get me all the height I wanted. I'd read about scissor trusses, but these were not technically scissor trusses.

If you don't need the 15' height at the sidewall, maybe something similar would work for you.

 

[billconner]

Raised tie truss. Makes building not look so tall, which is often nice.

 

[NUTTSGT]

I'm guessing either you aren't understanding what he's saying or that he's not understanding what you are asking.

Definitely not on the same page.

 

[billconner]

Going to try and find a second opinion but curious if anyone has succeeded in a similar build with 2x6 or even 2x8 at full 15 foot?

Someone here built or is building a 15'+ with engineered plans 2x8 12" o.c. iirc. In Massachusetts I think. Not sure you'd save any time or money over block and 2x6 (24" o.c.?).