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Control Joints in a Fire-Rated Gypsum Assembly

Q: How do I install a control joint in a gypsum panel ceiling that is part of a fire-rated assembly?


A: Gypsum assemblies need to allow for movement in all conditions, including structural and non-structural partitions, ceilings and both fire resistive or non-fire resistive. Guidelines for the placement of control joints can be found in ASTM C840, Standard Specification for Application and Finishing of Gypsum Board. Focusing on ceiling applications, the standard calls for control joints in these conditions:


  • A control joint shall be installed where a partition, wall, or ceiling traverses a construction joint (expansion, seismic, or building control element) in the base building structure.
  • Control joints in interior ceilings with perimeter relief shall be installed so that linear dimensions between control joints do not exceed 50 feet and total area between control joints does not exceed 2,500sf.
  • Control joints in interior ceilings without perimeter relief shall be installed so that linear dimensions between control joints do not exceed 30 feet and total area between control joints does not exceed 900sf.
  • Control joints in exterior ceilings and soffits shall be installed so that linear dimensions between control joints do not exceed 30 feet, and total area between control joints does not exceed 900sf.
  • A control joint or intermediate blocking shall be installed where ceiling framing members change direction.


The standard also states that it is up to the architect to locate all control joints. A control joint is commonly achieved by installing a one-piece accessory that effectively and aesthetically divides the gypsum membrane into two separate membranes and allows for minimal movement between and independent of each other.

    

The standard does not address fire-resistive construction, but the dimensional requirements stated above are assumed to be met as well. Therefore, control joints are required in both interior and exterior ceiling systems that are part of a fire-resistive assembly.

    

Guidelines for the proper installation of the one-piece accessory can be found on UL LLC’s online certification directory, UL Product iQ™. At the top of every individual design is a link to “Guide Information for Fire-resistance Ratings.” Scrolling down through the index is Section III, Floor-Ceilings and Roof-Ceilings. Subsection nine, Ceiling Control Joints, is where the desired information resides. It provides guidelines that allow for a control joint in the gypsum ceiling while maintaining the fire-resistive rating of G500, L500 and M500 series floor-ceiling designs. The details are applicable to 1-hour construction that includes a single layer of 5/8-inch thick gypsum panels that are finished appropriately.

    

The detail starts with a maximum half-inch gap between adjacent gypsum panels. A one-piece control joint accessory is then stapled to the gypsum panel on both sides of the gap. This accessory can either be zinc or vinyl but must meet the requirements found in ASTM C1047, Standard Specification for Accessories for Gypsum Wallboard and Gypsum Veneer Base. For the ceiling framing, the guide assumes a conventional ceiling grillage system that incorporates 1 1/2-inch deep, 16 gauge channels that are suspended on 12 gauge steel hanger wires and oriented perpendicular to the control joint. Drywall furring channels, 7/8-inch deep by minimum 25 gauge are wire tied with a double strand of 18 gauge wire to the carrying channels and run parallel and on each side of the control joint. What is clearly shown in the published details is that the two channels are attached to different carrying channels. The requirement is that the two furring channels are free to move independent of each other.

    

Over the top of the control joint accessory is a strip of gypsum board. This is done to assure the continuity of the gypsum through the joint and thereby maintain the fire resistive integrity of the overall assembly. This 5/8-inch thick by 3 1/2-inch wide panel is attached to the gypsum panel only one side to the control joint with 1 1/2-inch long Type G screws at a maximum spacing of 24 inches on center. The type of gypsum must meet the specific design and should be oriented parallel to the drywall furring channels.

    

The guidelines do not cover the condition where multiple layers of gypsum board are required. One gypsum panel manufacturer has suggested that the number of gypsum strips installed over the control joint accessory must meet or be the same thickness of the layers of gypsum panels required for the rating.

    

Remember that the control joints required in the gypsum panel ceilings are a component in fire-resistive assemblies. As such, there are recognized details that must be followed to assure the fire integrity of the floor-ceiling assembly. These details should be acknowledged prior to installation and with the approval of the authority having jurisdiction over the project obtained.


Robert Grupe is AWCI’s director of technical services. Send your questions to grupe@awci.org, or call him directly at (703) 538.1611.

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