Balancing Risk and Performance in Cold-Formed Steel Framing for Superior Sound Design
As the use of delegated design increases, wall and ceiling contractors are taking on more liability for meeting acoustical, fire, and other performance requirements. PAC’s expertise in acoustics, construction, and fire makes us an excellent partner for contractors working to meet these project requirements. In addition, PAC’s products like the RSIC-1®, RSIC-1® Backer, and the RSIC®-U HD have been tested and honed over more than two decades to provide high performance, while being cost-effective and easy to install.
About PAC
PAC is a multi-generation family-owned business with a long history in the wall and ceiling industry. PAC’s founder, Elzo Gernhart, started as a lather for Ceiling Systems, Inc. in Portland, OR in 1969. Since then, Elzo has:
- Run a drywall contracting company that built clean rooms for Intel and offices for Nike.
- Run a major drywall distribution company in the Portland, OR metro area.
- Served as an original member of AMAROK.
- Run an export business that supplied construction materials to US military bases.
- Revolutionized the acoustics industry with the invention and introduction of the Resilient Sound Isolation Clip, the RSIC-1, which provides a dramatic increase in performance and reliability compared to resilient channels.
PAC is now run by Elzo’s son, Mike Gernhart, who continues the family legacy by developing new and novel products that provide real-world solutions for construction. In 2021, PAC increased its commitment to providing high-level acoustical support by hiring Mike Raley, an INCE Board Certified acoustician with ten years of acoustical consulting experience.
Delegated Design
The AIA and AISC define Delegated Design as “… a form of collaboration between a design professional and contractor where the contractor assumes responsibility for an element or portion of the design.” In wall and ceiling construction that means the drywall/framing contractor is responsible for meeting the fire and acoustical performance criteria. While project design teams may include acoustical consultants, the contractor may not have easy access to them. This leaves contractors stuck trying to address the complexities of acoustical performance by themselves. They must understand the construction details that affect the STC and IIC performance of assemblies tested in a lab, and they must control the factors affecting these assemblies’ performance in the field. This can add considerable stress to over-taxed construction teams and increase the liability of the contractor.
Furthermore, there is an increase in the number of acoustical codes and standards and in the requirement for pre-occupancy acoustical testing. There are acoustical codes or guidelines for multi-family residences (IBC), hospitals (FGI), hotels (brand standards), schools (ANSI S12.60, CHPS, IBC), government buildings (agency standards), green buildings (LEED, WELL, IgCC, etc.), and many others. Previously, it was enough to have an acoustical lab test that showed an assembly met the project’s STC requirement. Nowadays that’s often not enough, and jurisdictions like Minneapolis and much of Canada are requiring pre-occupancy acoustical testing in multi-family projects. In delegated design projects the contractor now bears the responsibility for providing acoustical test reports and ensuring that, when tested, the constructed assemblies meet the performance criteria. This adds complexity and liability for the contractor and is where PAC’s products and extensive experience in acoustics, construction, and fire can help.
PAC’s RSIC-1 Provides Well-Documented and Consistent Acoustical Performance
Recent acoustical testing shows that PAC’s RSIC-1 eliminates the variability in acoustical performance due to changing steel studs’ gauge and spacing. The RSIC-1 is made of a steel claw that holds a typical 5/8” drywall furring channel and a rubber isolator that reduces sound transmission between the furring channel and the structural framing. When the gypsum board is attached directly to the steel studs, the STC rating of a wall can change by nine points or more just by changing the gauge and spacing of the studs (see table in Figure 1). Using resilient channels to isolate the gypsum board reduces the variation, but that variation is still enough to cause a typical wall to dip below the common requirement of STC 50. In comparison, when tested with the RSIC-1, the variation is reduced to one point, which is within the standard test variability and therefore insignificant.
Why does this variation matter to contractors? Imagine a load-bearing CFS-framed building where many of the load-bearing walls must meet minimum STC 50. Available acoustical test results for CFS walls are based on 18mil (25ga) or 30-33mil (20ga) steel studs. Per the Table, the walls tested with no isolation did not meet STC 50. There are other tests publicly available in which 18mil (25ga) steel studs spaced at 24” on center do achieve STC 50. However, for a load-bearing wall, 18mil (25ga) studs cannot be used, and the minimum stud thickness required is 33mil. Unfortunately, using 33mil studs results in a lower STC rating and a wall that will not meet the STC 50 requirement. The issue becomes worse as the walls on lower floors must carry higher loads and be framed with even thicker studs. These walls, 54mil (16ga), have ratings of STC 38-40, far below the STC 50 requirement. Using resilient channels improves the STC ratings, but it’s not enough to make the 54mil (16ga) stud walls meet the criteria.
One common solution is adding layers of gypsum board to increase a wall’s STC rating. However, this creates the following issues:
- The wall design is not consistent across all floors, which adds complexity and risk if the new wall schedule is not followed carefully.
- If the architect specified the wall width based on a single layer of gypsum board on each side, then adding a layer of gyp. creates a thicker wall that does not meet the design intent.
- Adding gyp. to walls adds costs that are not captured in initial bids.
- Additional wall width has knock-on effects for items like door frames that are sized for a specific wall width, and these secondary changes may be missed.
- Additional gyp. may increase the building loads enough to require revised structural calculations for static loads and the dynamic loads from seismic events.
Using the RSIC-1 eliminates these issues because it provides consistent performance regardless of stud gauge or spacing. This means the contractor can change the stud gauge and spacing to optimize the wall to minimize labor and material costs without compromising acoustical performance. The RSIC-1 has the added benefit of reducing the number of gypsum board layers required to achieve an STC rating, as evidenced by the comparison of the RSIC-1 and resilient channel wall designs at the top of Figure 1.
Stud gauge and spacing issues are not limited to load-bearing walls. For example, the Tile Council of North America (TCNA) requires that the steel studs for tiled walls are a minimum of 20ga (33mils). Even thicker/stiffer studs may be required for large-format tile and natural stone. Heavier gauge studs may also be required in non-load-bearing walls when mounting items like grab bars and specialty A/V equipment. These requirements mean that even a single wall, such as a condominium demising wall, may require more than one stud gauge–another layer of complexity and a source of liability.
Last of all, the RSIC-1 provides far greater reliability compared with resilient channels. The majority of acoustical testing over the years has been done with RC-Deluxe, which can be identified by its distinctive dog-bone shaped cutouts. Acoustical studies show that other types of resilient channels used in walls can perform 3 to 7 STC points lower than RC-Deluxe1. Additional studies show that short-circuiting the channels can reduce the acoustical rating of a wall by up to 9 points2. Further information on such issues can be found in the referenced papers, and in the blog posts by the acoustical consulting firm ABD Engineering and Design3,4.
Design and Construction Details for Good Acoustics
As more and more projects require pre-occupancy testing for performance verification, it is no longer sufficient to provide a test report that shows a wall meets the project’s STC requirement. Contractors must also address the often-complicated design and construction details for penetrations, intersections, and wall-mounted objects.
An often overlooked detail is how to mount heavy items like cabinets on a wall that contains acoustic isolation. Half-inch plywood or OSB is often used as backing for cabinets on walls with resilient channels (see Figure 2). The cabinets are typically screwed into the backing, as well as the studs or blocking behind it.
PAC’s testing shows that this dramatically reduces the acoustical performance of the wall, taking an STC 54 wall down to STC 46 (see Figure 3). Fortunately, PAC has products that provide a stable mount for the cabinets while maintaining the acoustical performance of the wall. On walls with resilient channels, the PAC-RCB is the go-to solution, and on walls with the RSIC-1, it’s the RSIC-1 Backer. Both products have been tested and shown to maintain the acoustical performance of the base wall (see Figure 3 and the lower assemblies in Figure 1).
PAC International has extensive testing to support the performance of the PAC-RCB and RSIC-1 Backer, and both products are UL-listed for fire-rated wall designs. They are the only UL-listed products for the acoustic isolation of cabinets and other heavy wall-mounted objects. PAC has also performed in-house load testing to verify that the PAC-RCB and RSIC-1 Backer can withstand the 200 lb. load requirement for handrails and the 250 lb. load requirement for grab bars.
One final detail to consider is the acoustic isolation of the top and bottom tracks of a wall. This detail is less common in standard construction. Still, it is prevalent when high levels of sound isolation are desired, such as in performing arts venues, recording studios, and high-end condominiums. In typical construction, a wall’s top and bottom tracks are rigidly connected to the ceiling above and the floor below. This rigid connection creates a path for airborne and impact sound to travel from the floor or ceiling into the wall. This is called a flanking path, which is when sound goes around, or flanks, a sound barrier. PAC’s RSIC-U HD isolates the top and bottom tracks, eliminating this flanking path. The RSIC-U HD consists of a rubber isolator mounted in a steel plate. The steel plate is screwed to the track, and the rubber isolator is screwed to the structure (see Figure 4). The RSIC-U HD provides a mechanical connection to both the track and the structure, which results in a more secure connection. Consequently, the RSIC-U HD is approved for use in seven UL fire-rated dynamic head-of-wall details.
The RSIC-U HD is a versatile product that can be used for many applications besides isolating wall tracks. Over the years, PAC has used the RSIC-U HD to isolate wall-mounted electrical equipment, floating floors, projectors, and even targets for axe throwing.
Conclusion
The products discussed here are just a small sampling of the 80+ acoustical products that PAC offers, and we are continuously developing new products. Many of our products have been developed to provide acoustical and/or construction solutions for contractors with unique project challenges. As acoustical requirements become more complex and contractors take on more liability, PAC is here to help with our range of products and expertise in acoustics, construction, and fire. We also have a wealth of online resources, including our acoustical assembly test databases, our fire-design selector, our product selector, and our archive of webinars. This archive includes a recent webinar on spring-hung ceilings, organized by AWCI and co-presented by PAC’s Director of Engineering, Mike Raley, and AWCI’s former Director of Technical Services, Don Allen.
We are a small family business, so when you call us, you don’t get an automated answering system; you get a real person and are always no more than one transfer away from talking to the COO or Director of Engineering for help with your project. Give us a call and see for yourself. 866-774-2100
