Head of Wall Fire Ratings
Donald E. Smith, CCS
April 2009Just when you think you have seen it all, another one comes along. A member called the other day with a question about head of wall details. He was bidding on a renovation project involving drywall partitions in an existing concrete frame building. There were only two requirements specified for the head of wall. The first stated that it had to comply with the requirements of the New York City Building Code. The other specified compliance with UL 2079. Not much to go on, is it? The architect included only some details of a slip track with filler for the flutes in metal deck.
So what’s a guy to do? We can be pretty sure that the architect did not do the research necessary to specify the correct details. Second, UL 2079 is the test used for head of wall; it is not a design. UL does have designs just like the wall designs used in specifying head of wall. In fact, UL has designs for all of the perimeter conditions that maintain the integrity of a fire-rated assembly.
A quick search of the New York City Building Code 2008 edition references UL 2079 and requires the joints in the wall assembly, floor, head and edges, maintain the specified hourly rating for the wall assembly. No real surprise here as just about all jurisdictions use the International Building Code as their model code, and the IBC uses references to standards throughout.
UL has designs for head of wall that you can access along with designs for other perimeter conditions on the UL Web site, www.ul.com. Just click on the online certification directory. The key to locating the correct design is to follow the numbering system assigned by UL.
An example for the situation at hand would be HW-S-0062. The HW is for Head of Wall, the S indicates that the joint is static, and the four digits indicate joint width. These designs list the rating value in hours, and in many cases they refer back to a specific UL design. Also, just as they do for the wall designs, they list the manufacturer of the products used.
The other designators are FF—floor to floor, WW—wall to wall, BW—bottom of wall, and CG—wall to wall joints intended to use as corner guards. If the movement is expected in the joint, then it is designated as dynamic and a D would replace the S in our example.
The series of four numbers indicates the nominal joint width and also designate a particular design. In our example, the series of 0000–0999 covers joints of less than or equal to 2 inches. There four more groups for a total of five groups of covering different widths. 1000-1999 covers greater than 2 inches and less than or equal to 6 inches; 2000–2999 covers greater than 6 inches and less than 6 inches and less than or equal to 12 inches; 3000–3999 covers greater than 12 inches and less than or equal to 24 inches and finally 4000–4999 covers greater than 24 inches. I give you this information just so you know it is available; I do not expect you to have to design the system.
In the case we are dealing with, the solution was a very simple one. In order to maintain the integrity of the required fire rating, sealant is the only material needed to fill the gap at the head of the wall.
So how could all on this extra work have been avoided? First, if the architect had done the research and provided the correct information in the beginning, there would not have been any problem. Another solution that may well be in the near future is the use of Building Information Modeling programs. BIM would have embedded information in the object file for a wall system that would point to not only fire-rated assemblies but to the corresponding joint systems required to maintain the fire rating of the specified assembly.
This object oriented filing system already exists. CAD programs have always been object oriented and come with a library of the most commonly used symbols for the designer or draftsman to select from during the process of producing a drawing. Each symbol used to produce a drawing has a file name that contains the characteristics of the symbol selected to indicate a given condition.
The problem for wall and ceiling contractors is that most of the symbols that pertain to our work are just lines; however, those simple lines convey a lot of meaning. As an industry we need to educate the software producers and the folks who build the symbol libraries that there should be symbols representing wall and ceiling assemblies. AWCI is working on this so that in the future, the end user of the drawings knows exactly what those simple lines represent. This would give true meaning to building information modeling.
Donald E. Smith, CCS, is AWCI’s director of technical services. Send your questions to firstname.lastname@example.org or call him directly at (703) 538.1611.