There’s something that architects need to be aware of as we use increasingly thicker continuous insulation behind masonry veneer cladding.
If the distance between the structural steel backup and the back of the masonry veneer cladding exceeds 4-1/2 inches, the masonry veneer anchor spacing must be designed by a structural engineer.1
Masonry veneer anchor spacing is not usually designed by a structural engineer; the code provides prescriptive requirements that we typically follow, and this spacing is most often indicated in the specifications by the architect or the structural engineer.2
Manufacturers of some types of masonry veneer anchors indicate that the legs of the anchors can accommodate up to 4 inches of insulation. But even these can’t be used without having calculations run by an engineer, unless you keep the distance between the structural steel backup and the back of the masonry to 4-1/2 inches. (This would leave very little air space. You need at least 1 inch of air space, per the code, and an air space of 2 inches is recommended by the Brick Industry Association.3)
By the way, these things aren’t spelled out in the text of the International Building Code. They’re in a separate document that is incorporated into the IBC by reference, the TMS 402/ACI 530/ASCE 5. This document is called “Building Code Requirements for Masonry Structures,” and is developed by the Masonry Standards Joint Committee (MSJC). Since it’s referenced in the IBC, it becomes part of the requirements of the IBC.4
So, architects, either stick with 4-1/2 inches or less between the structural steel backup and the back of the veneer masonry, or let your structural engineer know, as soon as possible, that you are exceeding 4-1/2 inches. If it’s too late for your project, sometimes the masonry veneer anchor manufacturer who gets the project will hire a structural engineer to check (or design) the anchor spacing. The cost of this service would get passed on to the general contractor and then to the owner (as an extra cost). Avoid a construction change order – deal with this on the design side, before construction starts.
- Chapter 12, section 184.108.40.206.4 of the latest version of TMS 402/ACI 530/ASCE 5 indicates that “A 4-1/2 inch maximum distance between the inside face of the veneer and the steel framing shall be specified. A 1 inch minimum air space shall be specified.” There are alternative procedures allowed by the code that can be used instead of these prescriptive requirements, but the alternative procedures are what require a structural engineer to design the anchor spacing.
- Chapter 12, section 220.127.116.11.6 of the latest version of TMS 402/ACI 530/ASCE 5 tells us the prescriptive requirements for anchor spacing: “For adjustable two-piece anchors, anchors of wire size W1.7, and 22 gage corrugated sheet-metal anchors, provide at least one anchor for each 2.67 ft2 of wall area.
“Space anchors at a maximum of 32 inches horizontally and 25 inches vertically…”
- The Brick Industry Association publishes online Technical Notes on Brick Construction. Here’s a link to their Technical Note on “Brick Veneer/ Steel Stud Walls.” http://www.gobrick.com/portals/25/docs/technical%20notes/tn28b.pdf
- Section 2101 of the 2012 IBC indicates that “Masonry veneer shall comply with the provisions of… TMS 402/ACI 530/ASCE 5.”
Very interesting. I’ll have to check that in our Canadian and provincial building codes too.
It’s interesting that TMS 402/ACI 530/ASCE 5, Chapter 12, limits the maximum distance between the inside face of the veneer and the backup to “steel framing” backup. Would the same distance restriction apply to a CMU inner wythe? Logically it would. Also, although a 2-piece veneer anchor similar to that used with cold-formed studs could be used with CMU, more likely the anchor would be the type that engages projecting eyelets from continuous steel reinforcement of the CMU.
Yes, basically the same thing for non-composite double wythe masonry walls –
“Specified distances between wythes shall not exceed 4.5 in. (114 mm) unless a detailed tie analysis is performed.” (section 18.104.22.168) That section also gives tie spacing.
Very good piece!
Do you have a list of topics you want to cover, or are they
your random thoughts?
Any recent contacts or info about our Task Team report?
Ralph W. Liebing, RA, CSI, CDT
Senior Architect- Specifications
Sometimes I have topics I intend to cover, but they come from my random thoughts. This one had been bouncing around in my head for a while, since I encountered this on a project (caught it before it went to bid), so I’d meant to write about it for a while, and hadn’t had time.
Nothing new on our Task Team report.
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