Gypsum Area Separation Walls Provide Effective Fire Resistance, Sound Attenuation

Multi-family housing designs using gypsum board area separation walls fill the bill

By Michael Gardner

         Effective fire resistance and sound attenuation have long been important considerations in the design of multifamily dwellings, such as townhouses, condominiums, and apartments. Gypsum board systems represent an effective and inexpensive solution for area separation walls—sometimes referred to as fire walls, party walls, or townhouse separation walls. Gypsum area separation walls are easy to erect and secure, and they meet all building code requirements. Fire resistive ratings easily reach two hours and more. And they can be erected up to four stories in height, depending on the manufacturer. 

Gypsum board area separation wall systems weigh no more than 10 pounds per square foot when erected—far less than alternate construction materials. In most cases, gypsum board's light weight eliminates the need for costly footers or foundation modifications. In fact many systems can be erected directly onto a poured concrete slab.

Complying with Codes

Any area separation wall must meet certain basic requirements. It must be: 

             Every model building code recognizes the suitability of gypsum board area separation wall systems for resisting fire and attenuating sound. Though gypsum has inherent fire-resistive qualities, each model building code mandates that any wall system used for area separation must first be fire tested according to a specific test standard, such as ASTM E 119,"Standard Test Method for Fire Tests of Building Construction and Materials," or its equivalent.

 These test standards produce numerical ratings that can be used as a benchmark for comparing and evaluating fire-resistive systems. Fire-resistance classifications are the results of tests conducted on assemblies made up of specific materials put together in a specified manner.

 Model building codes for townhouses and condominiums usually require units to be separated by a two-hour fire-rated wall system. A design for a successful and compliant gypsum area separation wall should not deviate from that described in the test report. Nor should the system include materials not evaluated in the original fire test.

Solid Gypsum Area Separation Walls

         Gypsum board area separation wall systems come in two designs: solid systems and cavity-type systems. Cavity systems are constructed with components typically incorporated into either steel stud partition systems, or gypsum board shaft wall enclosures, such as those used to enclose an elevator shaft or duct shaft in a multi-story nonresidential building. 

 Solid gypsum board type area separation walls systems incorporate three basic components: 

         For two-hour fire resistance, the area separation wall consists of two layers of 1-inch thick liner panels. The panels slide into a horizontal track at the foundation or floor level and into the vertical studs that hold them in place. An inverted section of track caps the wall. To continue the wall higher, a track is fastened to the capping track of the lower wall. The stacking process repeats until an inverted track caps the completed final story or roof parapet.

 L-shaped aluminum clips attach the gypsum board area separation wall to the adjacent wood frame structure. The clips attach to both sides of each H-stud at each floor or roof/ceiling intersection to provide lateral support for the area separation wall. The clips are designed to soften and break when exposed to high temperatures on the fire side.

 During an intense fire, when one side of the wall system experiences temperatures of    1100 °F or higher, the clips will soften and break away. In this way, the adjacent structure on the fire side may collapse without pulling down the fire-resistive separation wall. The clips on the opposite side of the area separation wall remain intact, since temperatures on that side will be far below the point at which the clip will soften. As a result, the fire-resistive wall system will remain standing, sparing the adjacent living space from significant damage.

         The clips must be manufactured from aluminum in a thickness and shape conforming to the requirements established by the representative fire test and the manufacturer of the area separation wall system. Otherwise the wall system may not function as intended.

Ensuring a Successful Installation

               The components of a gypsum board area separation wall system must be protected from adverse weather and extreme or continuous moisture during and after the installation. Gypsum panels must also be shielded from sustained temperatures exceeding 125°F (52°C). This means gypsum board should not be installed in a sauna, steam room, or where it will be directly exposed to the immediate heat produced by such appliances as a wood-burning stove.

              In addition, the area separation wall system must be disconnected from adjacent combustible framing members to be fully code compliant. The representative fire test states how close the wood framing members may be set to the area separation liner panels—usually ¾ to 1 inch. If the space requirement cannot be met, the visible faces of the H-studs must be covered with 6-inch-wide gypsum board batten strips, full sheets of gypsum board, or mineral fiber insulation.

Building codes also typically require the space between the area separation wall and the adjacent floor joists to be fire blocked to prevent fire from spreading vertically between floors. This can be achieved easily by requiring continuous pieces of one-inch gypsum board liner panel, mineral fiber insulation, or other code-allowed material into the gap between the wall assembly and the adjacent floor joists. Fire blocking material should be firmly attached to adjacent construction. Manufacturers offer typical construction details for foundation and intermediate floor junctions, exterior wall intersections, roof junctions, and roof parapets.

 In short, gypsum board area separation walls offer an excellent low-cost solution for separating townhouses, condos, and apartments. They are code compliant for both fire resistance and sound attenuation. 

Michael Gardner is Director of Promotion and Code Services for the Gypsum Association, a trade organization that represents leading gypsum board manufacturers in North America.