The most interesting things that come across my desk usually come out of California. Just recently one of AWCI’s distributor members on the West Coast posed a question about control joints in gypsum sheathing. Yes, you read it correctly: control joints in gypsum sheathing. To be a little more concise, we are talking about glass mat gypsum sheathing. The old brown board, while still available, is not in common use any longer, and the governing installation standard has been revised to reflect new requirements for glass mat gypsum sheathing.
I have to say this was a bit of a surprise. Not being sure of what this was all about, I made a few inquiries of my contacts within the gypsum industry and found that it is true. ASTM C1280-11, Standard Specification for Application of Gypsum Sheathing, requires the placement of control joints every 30 feet. Knowing that the semiannual meeting of ASTM Committee C11 was in the offing, I decided make inquiries at the task group meeting for ASTM C1280. The outcome was another surprise—and one of those things that comes back to bite you.
I was told that there was a need for the control joints because the building moves and can cause a disruption to the sheathing resulting in damage to the finish cladding. Of course this is not a desirable outcome. Control joints are something we have to live with and something that architects do not like. Other sheathing materials require you to leave gaps between panels. In OSB sheathing beneath stucco, we have to leave a 1/8-inch gap to accommodate movement in the panels. But there is no requirement for a control joint in OSB, plywood or generic gypsum sheathing.
Bear in mind that the intent in C1280 for a control joint is just that—a control joint similar to what you would use in drywall. This also means that the control joint must go through the finish cladding.
Who Rules?
This makes me wonder if there is more movement in glass mat gypsum than there is in any other sheathing. I have seen the results of not providing a control joint where it is needed, and I fully understand the need to accommodate movement in the structure. But in all my years in this industry I have never put a control joint in sheathing material unless it was required by the finish cladding.
Some manufacturers of glass mat gypsum sheathing do not require the inclusion of control joints in their sheathing products. Period.
The problem in the case in question is that the inspector is looking only at the ASTM standard. He really does not care or look at the manufacturer’s recommendations for the product installation. The ASTM standard is the final word, and there is no wiggle room.
Where Do We Go From Here?
You all are very much aware of my feelings about ASTM and its role in how we conduct our business. Well, this is where it comes back to bite you—or least it came back to bite me.
The task group decided with the approval of the subcommittee chairman (that’s me) that they should establish a new task group to look into the requirement for control joints in glass mat gypsum sheathing. Would you like to hazard a guess as to who was asked to head this new task group? Yes, it is me. Now what do I do?
First I have to look at the product in question. Does it move more than other sheathing materials? What makes this product different from other sheathing materials? Can we convince the manufacturers who want the control joint requirement to change their minds about the need for a control joint? These types of questions always come up when ASTM standards need to be revised.
At this point I need to gather as much information as possible to remove the requirement for control joints in glass mat sheathing. This product has been in use for a long enough period of time to arrive at significant conclusions. If you have any experience, good or bad, please pass them along.
When it comes to ASTM installation standards, those of us in the user classification must make our voices heard. While the manufacturers have valid concerns and liabilities for their products that we install, we are ultimately the ones who bear the performance burden.
I realize that not everybody has to stand up to the scrutiny of inspectors like the ones from the State of California Office of Statewide Health Planning & Development, but there is always the possibility of an encounter with an inspector with the same mind bent.
Donald E. Smith, CCS, is AWCI’s director of technical services. Send your questions to [email protected], or call him directly at (703) 538.1611.
