Anchored CMU Veneer Above 30' Height Limit
Anchored CMU Veneer Above 30' Height Limit
(OP)
All,
I saw a couple old threads on this that were great, but they are closed and I'd like to take up the issue again. I'm designing a wood framed building (including wood shear walls) with a CMU decorative veneer. The top of wall elevation is consistent (small sloped roof) at 42'. I understand the use of the 30' limit in Chapter 6 of TMS-402, but I'm curious about what people consider the "Alternative design" in TMS-402-08 section 6.2.1 allowing unlimited height.
My thoughts:
1. 42' doesn't concern me as long as I take in to account wood shrinkage, CMU thermal expansion, CMU shrinkage, and inform the architect to account for such details.
2. I know shelf angles to wood are used, but I feel like that is potentially more problematic than going an additional 12'. Those detail introduce wood creep, proper angle installation, expensive difficult to build details, etc.
I'm curious what other things you all would consider for the rational design using 6.2.1, and if you've used it successfully?
Thanks,
Nick
I saw a couple old threads on this that were great, but they are closed and I'd like to take up the issue again. I'm designing a wood framed building (including wood shear walls) with a CMU decorative veneer. The top of wall elevation is consistent (small sloped roof) at 42'. I understand the use of the 30' limit in Chapter 6 of TMS-402, but I'm curious about what people consider the "Alternative design" in TMS-402-08 section 6.2.1 allowing unlimited height.
My thoughts:
1. 42' doesn't concern me as long as I take in to account wood shrinkage, CMU thermal expansion, CMU shrinkage, and inform the architect to account for such details.
2. I know shelf angles to wood are used, but I feel like that is potentially more problematic than going an additional 12'. Those detail introduce wood creep, proper angle installation, expensive difficult to build details, etc.
I'm curious what other things you all would consider for the rational design using 6.2.1, and if you've used it successfully?
Thanks,
Nick






RE: Anchored CMU Veneer Above 30' Height Limit
RE: Anchored CMU Veneer Above 30' Height Limit
RE: Anchored CMU Veneer Above 30' Height Limit
RE: Anchored CMU Veneer Above 30' Height Limit
I have once, once, only once, informed the architect and they agreed to use fiber cement above the third story with a veneer expansion joint at the transitions.
But typically it is brick shelves for me, hopefully you have a small wall cavity. And hopefully they do not require continuous insulation on the exterior of the sheathing (2 more inches of cantilever! => L8x8 all around!)
RE: Anchored CMU Veneer Above 30' Height Limit
I agree. It's almost a license to do what you want. Rare you see that in the code, which is one reason I want to think through it a long time before I utilize it.
@mike20793,
I'm in a 90mph wind area (still on ASCE7-05 here), and the pressures aren't too bad. As for supporting the brick at each level. I worry about the contractor not installing the detail well more than shrinkage. Have you had success with contractors doing that well?
@XR250,
Thanks!
RE: Anchored CMU Veneer Above 30' Height Limit
RE: Anchored CMU Veneer Above 30' Height Limit
I would not recommend using relieving angles. That is a lot of steel that will not be properly installed.
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
RE: Anchored CMU Veneer Above 30' Height Limit
The wood framing, with presumed wood shearwalls, will sway some distance horizontally under wind loads and the brick veneer won't tend to move at all.
So at top floor window openings you have the interior stud walls and window framing moving laterally while the brick around the windows is not moving much at all.
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RE: Anchored CMU Veneer Above 30' Height Limit
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
RE: Anchored CMU Veneer Above 30' Height Limit
RE: Anchored CMU Veneer Above 30' Height Limit
RE: Anchored CMU Veneer Above 30' Height Limit
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
RE: Anchored CMU Veneer Above 30' Height Limit
But have you've seen a lot of 42 ft. tall veneers not get affected?
My comment was just a suggestion that with a much higher building than the typical 30 ft. veneer, then lateral sway might be a problem to at least consider.
I don't think it is a good idea to just ignore it.
On the vertical shrinkage aspect, I've seen wood shrinkage wreak havoc with brick veneer when the architect failed to separate the veneer from second floor windows.
The exterior wood studs and plates all shrunk and the brick veneer, set tight to the bottom of the windows didn't want to move down with the wall. The EIFS system above
also moved down with the studs and crushed itself at the brick line all around the building.
This kind of effect is also accentuated higher up.
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RE: Anchored CMU Veneer Above 30' Height Limit
We are actually using decorative CMU, not that it matters much in terms of load/anchorage. However, at least it won't be growing while the wood wall shrinks. With that said, I also plan to inform the architect of the need to detail joints for the wood to shrink and not negatively affect the wall.
JAE, what do you think about the fact that if I set the CMU veneer on a steel ledge beam above, I have wood creep and shrinkage to detail for also. I guess I don't see the difference between how important the details are between keeping the veneer solid to the foundation versus hanging it off the wall at 30'. Either way the details are critical. It's just a matter of where you detail the joints. My thought would be to avoid hanging it and detail joints elsewhere. That would save money and eliminate the CMU adding to wall creep. But I'm open to being wrong on this, just my reasoning to this point.
RE: Anchored CMU Veneer Above 30' Height Limit
It's also worth noting that architects have an easier time detailing the shrinkage if you give them a range of expected shrinkage. Since the change in moisture content isn't always known, I usually give a range of expected shrinkage. Also, you're not really going to have to worry about wall creep. The amount it will shorten based on the stud loads is usually accounted for in the range of shrinkage expectation.
RE: Anchored CMU Veneer Above 30' Height Limit
That's all I'm saying.
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RE: Anchored CMU Veneer Above 30' Height Limit
In my experience, I have never seen any drift related issues with 4 story brick on a wood framed building. I've designed maybe a hundred of these now in one shape or form and my office(s) have done another few hundred 4+ story stick with brick. Of course, this is in a low seismic, 90mph zone. Still, nothing after the last 15 years of storms and a minor east coast earthquake.
Of course, nothing is a problem until it is. I don't know everything, but I know a safe bet.
The masonry problems that I have seen are usually due to shrinkage and lack of detailing / joints.
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
RE: Anchored CMU Veneer Above 30' Height Limit
RE: Anchored CMU Veneer Above 30' Height Limit
RE: Anchored CMU Veneer Above 30' Height Limit
Are you suggesting a reinforced veneer that spans 13'-4" vertically?
A veneer is usually based on a back-up (CMU or steel stud) with adjustable ties that transfer the horizontal loads back into the basic structure.
It has been done with some CMU or clay veneers, but the detailing is very tricky.
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
RE: Anchored CMU Veneer Above 30' Height Limit
RE: Anchored CMU Veneer Above 30' Height Limit
RE: Anchored CMU Veneer Above 30' Height Limit
1. Attached are the elevations of some of the walls. I'm concerned about the veneer cracking at these window locations. What do you all think?
2. I'm still considering using the alternate method of the MSJC, IE supporting the veneer only off the foundation and going above 30'. The BIA (brick folks) have an article on how to do that. It's CMU veneer (decorative stuff), and not brick, but same concepts apply except it will shrink instead of grow.
3. What if I did a combination of supporting the veneer off the structure at the windows at each level, and off the foundation at the areas where the wall goes full height.
Just so everyone knows. The 1'-4" wide Piers between windows are backed with (2) 6x6 glulam posts that support 3-ply 1.75"x14" LVLs at floor levels. So there is a meaty core. Windows are 8'-0" wide.
Any comments?