Whether it’s the blaring stereo in the adjacent unit or a loud hallway conversation, multi-housing residents are profoundly bothered when noise disrupts their tranquility.
For multi-housing professionals, resident noise complaints mean lost dollars. Annoyance with noise can mean lost business from residents moving out, difficulty filling units due to negative online reviews, and staff time spent addressing noise complaints.
Whether you’re planning construction of a new multi-housing development, or adding buildings to an existing community, paying attention to the walls will go a long way toward quieter rooms—and happier residents.
A recently developed set of wall assemblies using structural insulated panels (SIPs) helps significantly reduce sound transmission in new buildings, while also meeting fire ratings. Plus, the assemblies are simple and fast to construct, helping your community open sooner so you can begin collecting rents.
Building codes and noise
While building codes typically focus on matters of life and property safety, and energy efficiency, noise is so troublesome to people that the International Building Code (IBC) has a section devoted to managing noise.
Specifically, the code requires certain building assemblies to meet a sound transmission class (STC) of 50 or greater for airborne noise. This degree of sound control means that stereos and musical instruments can only be faintly heard and that loud speech is not audible.
IBC Section 1207.1 calls out the areas that must meet this level of noise reduction:
“This section shall apply to common interior walls, partitions and floor/ceiling assemblies between adjacent dwelling units or between dwelling units and adjacent public areas such as halls, corridors, stairs or service areas.”
A typical way to meet STC ratings
Low-rise multi-housing buildings typically are built using stick framing—wood wall studs, joists and other members made of sawn lumber or engineered wood products like laminated strand lumber (LSL).
Meeting STC ratings of 50 or higher is labor and material intensive with stick framing. For example, a common method to achieve STC 55 involves building two rows of 2×4 studs staggered between the wall faces, with sound absorbing material placed on one side. One stick-framed assembly that rates STC 57 is to build a double wall on a common 2×6 floor plate, with absorptive material on both sides.
A better way using SIPs
Recently, wall assembly options have been developed that achieve high STC ratings, yet are faster and easier to construct than high STC stick-framed walls.
The heart of these assemblies are structural insulated panels (SIPs). Typically used for superior energy efficiency in the building envelope, SIPs are pre-built wall and roof components. SIPs are made of structural wood panels laminated to a rigid insulating foam core, and come in large sizes—up to 8 ft. x 24 ft.
As monolithic wall units with continuous insulation and few gaps to be sealed, SIPs are very air tight and are effective at stopping airborne ambient noise. However, the panels by themselves are less effective at blocking low frequency sounds.
To overcome this hurdle, Premier SIPs developed several wall assemblies using a proprietary clip, gypsum wallboard and fiberglass batt insulation, which have been independently tested to yield STC ratings of 48, 52, 58 and 59. The heart of each assembly is a standard foam core SIP. Directly attached to one side of the panels is 5/8-inch Type X gypsum wallboard. On the other side, a clip attaches to the SIP with a screw. Hat channels are then snapped into the clip and 5/8-inch Type X gypsum is then fastened to the hat channel. The clip minimizes the contact area of the various layers of the assembly, which helps decouple the assembly and reduce sound transmission. Additional sound dampening is achieved by adding 2-1/2-inch fiberglass batt insulation in the space between the SIP and gypsum that is created by the clip. The assemblies are non-directional, so the clip system can be installed on whichever side of the wall the architect or builder prefers.
One layer of gypsum on each side of the SIP yields an assembly with either STC 48 or STC 52. Doubling the gypsum on both sides boosts the noise reduction to STC 58 or STC 59, which is well above the IBC STC 50 threshold.
The assemblies with double layers of gypsum also achieve one-hour fire ratings, which adds another dimension of performance wherever an hourly fire-rated wall is required. Yet, for interior partition walls, which do not need to be fire rated, the single layer gypsum assemblies work well, as they still achieve STC 48 and STC 52.
All of these SIP assemblies are significantly easier to construct than typical wall types used to achieve the IBC’s required STC 50 rating.
Using SIPs for energy-efficient building envelopes
SIPS provide an energy efficient building envelope in three ways: a near airtight assembly, solid continuous insulation and reduced thermal bridging.
It is “dramatically easier” to make a SIP structure tight, because it “has fewer joints and less complicated interfaces between conditioned and unconditioned spaces,” said Sam Rashkin, a former national director of the U.S. Energy Star program. This is backed-up by rigorous research, including testing by the U.S. Dept. of Energy’s (DOE) Oak Ridge National Laboratory. The lab found that SIP structures are up to 15 times more airtight than traditionally framed walls insulated with fiberglass batts. A SIP structure’s air leakage rate was only 8 cu. ft. per minute at 50 Pascals of pressure versus stick framing with a leakage rate of 121 cu. ft. per minute.
In addition to reducing air leakage, SIPs provide solid continuous insulation across the panels’ height, width and depth for exceptional thermal performance by reducing convective looping. And, unlike traditional construction with studs, concrete or CMUs, SIPs have fewer thermal bridges to conduct heat.
Joe Pasma, PE, is the technical manager for Premier SIPs by Insulfoam, a division of Carlisle Construction Materials. He has more than 35 years of experience in the building industry, including structural engineering, product development, and application of building science principals. He can be reached at [email protected].