Maximizing the benefits of resilient channel
Resilient channel can be implemented to optimal effect as long as a tested, high-performance channel is selected, and the product installed correctly. Many materials comply with ASTM C645, Standard Specification for Nonstructural Steel Framing Members, but most have not been laboratory-tested and do not provide the installation instructions necessary for building professionals to achieve the rated performances described.
Selecting the proper channel starts with the proper design. Resilient channel is 13 mm (½ in.) deep, constructed using 25-gauge steel. It has a single-leg attachment point that adds a flexural component to incoming sound waves. Resilient channel further works to break any wave received by the wallboard by creating a path that attenuates vibration. The most effective means of accomplishing this has proven to be use of the ‘dog-bone’ slot. This slot runs parallel to the channel, and is 25 to 75 mm (1 to 3 in.) long and 9.5 mm (3⁄8 in.) wide, spaced 25 to 50 mm (1 to 2 in.) apart on the sloping side of the resilient channel. Holes are centered on the slots for attachment points at 406 and 610 mm (16 and 24 in.) on center (o.c.).
Potential issues with using resilient channel
Regardless of best efforts to plan and specify, successful project completion ultimately relies on the provision of detailed instructions for the products used in construction—including resilient channel. Without careful installation of these products, laboratory performances will not be achieved. The following list of installation instructions are adapted by this author from the guidelines of various drywall and channel manufacturers. However, they are not product-specific and cannot apply to all cases. It is best to seek specific instructions to ensure full success.
1. For walls, resilient channel should be installed at right angles to studs or joists, using 9.5-mm (3⁄8-in.) type S pan head screws with flange down—except at floor level, where the channel should be installed with the flange up. This can be substituted with a 13-mm (½-in.) layer of wallboard.
2. Where resilient channel must be overlapped, splicing is necessary. This should be completed by nesting the ends of the channel directly over the framing members at the proper spacing, to align the pre-punched holes.
3. When fastening resilient channel, screws should be driven into the channels between the studs or joists. The appropriate length of screw must be selected, and the location of the studs or joists identified, before attachment of the wallboard. Screwing the wallboard through the channel to the stud or joist destroys the ‘spring’ assembly that suspends it.
4. The ends of resilient channels should be held back from the side walls to eliminate binding against the wall. Ends should also be held off the top and bottom of a wall by a distance of 100 to 150 mm (4 to 6 in.). Where baseboard is used, screws cannot rigidly attach the base of the wall to the sill plate. Similarly, at the top of the wall, gypsum wallboard cannot be attached to the header.
5. Where a wall meets a resilient ceiling, a 6-mm (¼-in.) gap should be maintained to prevent supporting of the ceiling and grounding of the resilient channel. This gap should be filled with resilient caulk, and can be finish-taped.
6. Penetrations in a ceiling or wall should maintain the performance of the resilient channel and the integrity of the assembly’s sound transmission performance. Where lighting is attached to joists, it should project through the wallboard, allowing a 6-mm (¼-in.) gap on the perimeter. This should also be sealed with resilient caulk.
7. Resilient channels should be attached to the ceiling joists at right angles, as follows: 610 mm (24 in.) o.c. for joists 406 mm (16 in.) o.c., and 406 mm
o.c. for joists 610 mm o.c. It is best to use 32-mm (1 ¼-in.) Type W or S screws, but never nails, to fasten channels to joists. Channels can be fastened to joists at each intersection with the slotted hole directly over a framing member, and should be installed with mounting flanges facing the same direction.
Gypsum board should be applied with long dimension at right angles to resilient channels and end joints staggered. Spacing of 3 mm (1⁄8 in.) should be provided between the ceiling perimeter and adjacent walls and filled with acoustical sealant. It is best to attach boards with 25-mm (1-in.) Type S screws spaced 305 mm (12 in.) o.c. along channels, and not to fasten screws through the channel into wood joists. Joints between boards should be centered over the resilient channels, or be midway between channels with joints floated and backed with sections of channels. When correctly installed, a gypsum board/resilient ceiling system will slightly ‘give’ when pressure is applied.
8. To install resilient channels on wood- or metal-framed walls, one should attach resilient channels with the attachment flange down—except at floor level, where it should face up—and at right angles to the wall studs. A strip of gypsum panel can sometimes be used at the base of a partition in lieu of the first inverted resilient channel, and should be installed at a maximum of 610 mm (24 in.) o.c. Again, it is best to use 32-mm (1 ¼-in.) Type W screws, rather than nails.
For steel stud walls, it is important to position resilient channel at right angles to steel studs, space it 610 mm (24 in.) o.c., and attach it to stud flanges with 9.5-mm (3⁄8-in.) Type S pan head screws driven through holes in the channel mounting flange. Channels should be fastened to studs at each intersection, with the slotted hole directly over a framing member. Gypsum board should be applied perpendicular to studs, with long dimension parallel to resilient channels. It is best to provide 3-mm (1⁄8-in.) spacing between the edges of boards, floor, and adjacent walls, and to fill space with acoustical sealant. Boards should be attached with 25-mm (1-in.) Type S screws spaced 305 mm (12 in.) o.c. along channels, not fastened through the channel into wood studs. Joints between boards should be centered over the resilient channels. As with ceilings, a correctly installed gypsum board/resilient wall system will slightly give when pressure is applied to it.
9. Where soffits are constructed, they must not support the ceiling, as this will cause the resilient channel to fail. Soffits should be independent elements that are suspended with resilient channel. Cabinets mounted on resilient channel walls cannot be attached through to the studs, but rather must be mounted using toggle bolts to the wallboard alone.
Conclusion
Using resilient channel makes it possible to substantially increase the transmission loss properties of a wall, with only minor changes in the assembly’s thickness and weight. In office, education, and residential construction, using resilient channel in critical-rated assemblies has become a standard for efficient use of materials and labor. Selecting a channel with good test data and installation instructions can allow building professionals to achieve the performance criteria for any project.
Bill Stewart holds an undergraduate architectural degree from the University of Maryland at College Park, and a graduate degree in engineering acoustics from the Naval Postgraduate School in Monterey. He has studied HVAC system design at the University of Washington, and is a Recognized Education Facility Planner (REFP) for the Council of Educational Facility Planners International (CEFPI). Stewart is on the 2.6 Noise and Vibration Committee of the American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE), and is a member of the Acoustical Society of America (ASA) and Institute of Noise Control Engineering (INCE). He can be reached at bill@ssaacoustics.com.
