All Things Gypsum: Finishing Joints in Fire-Rated Construction, Part II
Fasteners are required to be spotted with joint treatment. Installation of a system without the necessary joint preparation can create a circumstance where the installed construction does not replicate the fire tested assembly–a condition that can create trouble on a project.
However, there are instances where you do not necessarily have to finish the joints in a fire-rated system, and knowing those circumstances might prove advantageous in the future. The specific situations are most commonly outlined in model building code language and code evaluation reports.
Take a Deep BreathBut before you stop fire-taping above every suspended ceiling, take a deep breath, exercise a bit of restraint, and contemplate a couple of basic thoughts.
First, systems that serve as part of the passive fire protection system in a structure often serve other multiple purposes. Many fire-rated gypsum partitions, for example, also serve as sound-rated walls. Simply because you can eliminate the fire-taping on a wood-frame one-hour wall because of code language that allows, it might not get you off the hook if the wall is also sound-rated, as sound-attenuating systems have to be sealed air-tight to function properly. The same thought occurs for assemblies that serve as part of a smoke migration prevention system.
In addition, you will be dealing with code language that is somewhat subjective and open to interpretation. Therefore, if you are planning on eliminating finishing of joints based on code language, you are advised to get a favorable opinion from the local jurisdiction that permits you to do as planned prior to beginning the process. You might be completely correct in your analysis, but a fight with “city hall” that begins the day you think you are done with an installation might cost you twice as much as would finishing the joints in the first instance.
So, let’s assume you have done your homework and you have a good relationship with the authority having jurisdiction. When does a model code permit you to eliminate finishing of joints and fastener heads in fire-rated construction? The basic language is in Section 2508.4 of the 2006 International Building Code (IBC), where it states:
2508.4. Joint Treatment. Gypsum board fire-resistance-rated assemblies shall have joints and fasteners treated.
Exception: Joint and fastener treatment need not be provided where any of the following conditions occur:
1. Where the gypsum board is to receive a decorative finish such as wood paneling, battens, acoustical finish or any similar application that would be equivalent to joint treatment.
2. On single-layer systems where joints occur over wood framing members.
3. Square edge or tongue-and-groove edge gypsum board (V-edge), gypsum backing board or gypsum sheathing.
4. On multilayer systems where the joints of adjacent layers are offset from one to another.
5. Assemblies tested without joint treatment.
Helpful ExplanationsThe IBC language seems fairly straightforward, but a bit of explanation might prove helpful.
Exception 5 is self-explanatory. No joint treatment in the fire test; no joint treatment required during installation.
Exception 1 largely reflects an archaic concept, since it is mostly applicable when systems incorporating batten strips are installed and, while popular in the 1980s and 1990s, those systems have fallen somewhat out of vogue in recent years. In essence, the exception permits the use of the joint protection system–the battens–to function in lieu of joint treatment. This makes sense; the battens typically perform better in a fire-resistant sense than a coat of joint treatment and applying both to a joint would create an unsightly mess.
The exception also can be difficult to implement because it often requires a subjective analysis of the ability of the surface treatment to perform in an equivalent manner as the joint treatment. Without a fire test on both systems, that can be difficult to accomplish. And if you have a fire test on both systems, then why not simply use the test?
That leaves exceptions 2, 3, and 4.
Number 2 can be explained by text derived directly from the IBC Commentary, “ ... where joints occur directly over wood framing members ... the additional joint treatment does not materially increase the fire rating of the assembly, and many partitions have been tested and passed ... without the added protection of joint and fastener treatment as part of the test design.” What is important to note are two points: One, the joints have to occur directly over wood framing members. Two, the language is specific to wood framing; it can’t be introduced as a concept on steel framing members.
Exception 3 is the language that allows the installation of gypsum sheathing without joint treatment. Gypsum sheathing is manufactured with either a square or tongue-and-groove edge that mitigates the passage of smoke and fire into a rated assembly. Note that “square edge” means exactly as it says; it should not be interpreted to mean that a tapered edge product is acceptable.
Number 4 is the most interesting exception, since it permits the installation of a multi-layer system without the application of joint treatment regardless of the type of framing member installed. Using the IBC Commentary again as a reference, it notes, “(m)ultilayer assemblies with offset joints will eliminate any gaps in the system; therefore, fire, smoke, and harmful gasses cannot penetrate the fire-resistance-rated assembly.” Note that a proper installation will require joints to be offset in accordance with the pattern established by the fire test. The code language does not permit variation from that principle.
Joint ConfusionSpeaking of joints, it is worth pointing out that the IBC actually uses the term “joints” in multiple contexts, a situation that can lead to confusion. As used in Chapter 25, the term “joint” refers to the common linear intersection created when two (or more) gypsum panels meet at an edge or at an angle. This is differentiated from the “joint” that is described in and defined in Chapter 7 as a “ ... linear opening in or between adjacent fire-resistant-rated assemblies that is designed to allow independent movement of the building in any plane caused by thermal, seismic, wind or any other loading.” The former instance is the joint in a wall or ceiling that is typically finished with joint treatment material. The latter instance refers to a separation between two separate fire-rated systems that requires a specific fire-resistive treatment method such as a specialized sealant system or joint cover. To visualize the latter circumstance, think of the joint that occurs at the head of a partition where it intersects with the underside of a rated concrete deck. Clearly, it is not the same condition as the joint between two panels in a wall or ceiling system.
While language similar to that for exceptions 2, 3, and 4 noted above also exists in Section 18.104.22.168. of ICC-ES Evaluation Report ER-1338, note that it does not exist in the 2006 International Residential Code (IRC); therefore, if you are installing a rated system and are working under the IRC, you need to refer to the Evaluation Report, along with the code, for guidance. Language in the Evaluation Report permits you to tie the concept back to standard test reference documents and facilitates the use of the concept in those few instances where a fire-rated system is required in a one- or two-family dwelling.
Again, the standard rule is to finish the joints and spot the fastener heads in fire-rated construction; however, there are exceptions. And if you know and understand them and apply them properly you might save yourself a lot of aggravation in the future. W&C