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Construction of commercial bldg. framing and roof design

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George1985

Nuclear
Mar 28, 2011
22
Are commercial buildings typically designed to have 8" CMU load bearing block walls, wooden trusses, with a metal roof? I'm no structural engineer or construction guy, but this sounds kind of fishy to me. Is CMU block sufficient for lateral and compression loading? Is wooden trusses with a metal roof typical?

Building Specs:
3775 sq. ft
10' ceiling
Loaded kitchen (stove, oven...etc)
Gabled roof

Thanks!
 
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Something along those lines are done all the time. BUT it does need some engineering to check walls and trusses, connections, etc.

Very common.
 
Depends a lot on where you are located, the budgetary limits, usage of the building, etc. What you described is a cheap type of construction...maybe ideal for some purposes in some locations, but not in others.
 
If this light gage metal for the roofing, there would have to be plywood sheathing under it to serve as the structural diaphragm.

Usually, though, commercial buildings have very flat 1/8" to 1/4" per foot roof slopes, and metal roofs do not serve very well in that condition. PEMB's commonly have minimum roof slopes of 1/12, four times that of commercial flat roof buildings.

Mike McCann
MMC Engineering
 
26 Ga. metal roofing
roof slope is 6/12.

wood trusses
cmu block wall

sheathing is the same as roof decking? could i use a steel deck with wood trusses and metal roof?
 
no that is not specified. only thing that is specified is:
"metal roofing"
"wooden trusses"
"8" CMU walls"
Etc.
Very vague, leaving the design up to the contractor.

I'm only checking what the owner is specifying to the contractor.
 
M^2 - I humbly disagree...

Many lighweight steel sheet fabricators have very well documented shear values for these products - esp using wood trusses or purlins at 2'-0'' oc. Maybe not your favorite idea nor mine - but they do work... Fifty years of experience has proven that.

BTW - NOT standing seam - that does need plywood!!!

 
You don't say how high the structure is to be. 8" walls with no piers/stiffeners would be fairly limiting.
 
There is nothing wrong with this structural system at face value, but it does need to be engineered. Calling out vague descriptions of CMU, sheathing, and especially the wood trusses doesn't cut it.
 
The horizontal diaphragm can be at the ceiling level. Works much better than on a 6/12 slope. I agree that metal roofing should not be used as sheathing.
 
The nominal top or side screwing of the raised joints of the metal roofing lend to the diaphragm shear not being developed very well if at all. It's not just the gage of the metal roofing, it's the structural pattern of the decking too.


Mike:

I have seen that too, but I would never do it in a commercial structure. Perhaps a farm building.

Remember that the CMU walls mentioned will contribute to the lateral forces on the diaphragm, and the size og the structure, coupled with the CMU walls, could make the metal roofing diaphragm concept very, very tenable at best. Then again, maybe wind controls...



Mike McCann
MMC Engineering
 
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