Implementing smarter sound control strategies

by Katie Daniel | September 6, 2016 2:58 pm

By Robert Marshall, P Eng., BDS, LEED AP
Continuous urban population growth in recent years has created one common problem in cities throughout Canada—noise complaints. In fact, a survey conducted last year by the City of Toronto revealed that 82 per cent of people were unhappy with the current noise levels of their neighbourhoods. Fifty-four per cent of those people also said they had previously filed a noise complaint. The City of Ottawa reported 6152 noise complaints were received in the first eight months of 2015, and the populations of other cities have also acknowledged substantial noise problems, such as construction, loud music, and noisy neighbours.

Naturally, the potential for noise complaints is magnified in urban multi-family housing, as hundreds of occupants are placed in close proximity to each other. Sound control is therefore becoming a prominent factor in the design of new apartment, condominium, and townhouse complexes. Prospective buyers and tenants who have previously dealt with excessive noise are likely to seek out new living spaces with walls that absorb or dampen sound before it reaches nuisance level. Likewise, design/construction project teams with the ability to cost-effectively provide sufficient sound control in the walls of residential units are sure to find themselves with plenty of work.

Before looking at wall assembly materials, however, it is important to understand sound control, the impact it has on living spaces, and the building standards guiding acoustical design in the multi-family residential market.

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Sound control
Sound control is essential in the creation of comfortable and healthy interior environments. Several scientific studies[2] over the years, such as Health Canada’s 2014 “Community Noise and Health” study and BioMed Central’s 2015 study, “Socioeconomic Status and Environmental Noise Exposure in Montréal, Canada,” have proven the negative impact of excessive airborne sound from inside and outside buildings—commonly known as ambient noise—on building occupants. Quieter spaces simply result in happier, more satisfied owners, tenants, patients, and students, which leads to quicker recovery times in healthcare environments and higher learning in classrooms. (For more information, refer to World Health Organization [WHO] guidelines for acceptable noise in patient rooms and ANSI 12.60, Maximum background noise level for Classrooms.)

One of the most effective ways to achieve acceptable ambient noise levels is to build wall assemblies that significantly reduce passage of airborne sound between residential units. The measurement for this effectiveness is the sound transmission class (STC) rating. The higher the STC rating, the more airborne sound transmission restricted by the assembly. Conversely, lower STC ratings mean more sound is transmitted through the wall assembly, which increases the ambient noise level of the space and contributes to a less-than-pleasant interior environment for those who live there.

STC ratings
Airborne sound does not simply pass through interior walls. Sound generated on one side of a wall actually energizes the wall structure and puts it in motion, much like a diaphragm. The wall itself becomes the transmitter of the sound energy, which can be heard on the opposite side of the wall. Therefore, the ASTM test methods used to determine STC ratings have focused on this direct transmission process. Currently, the STC number is derived from sound attenuation values tested at 16 standard frequencies from 125 to 4000 Hz. These transmission-loss values are then plotted on a sound pressure level graph and the resulting curve is compared to a standard reference contour. Acoustical engineers fit these values to the appropriate transmission-loss (TL) curve to determine a final STC rating.

Currently, the National Building Code of Canada (NBC) requires low- and high-rise residential construction projects to achieve a minimum STC rating of 50 in wall assemblies separating two residential units and corridors; and a rating of 55 for elevator shaftwalls that border a living space. These ratings can certainly be achieved with the right mix of high-performance gypsum wallboards and sound-absorbing or sound-dampening materials in an assembly.

Contemporary sound control methods
Unfortunately, many contemporary sound control strategies for wall assemblies have become known for being either too expensive or problematic to install. Often, even minor installation errors can compromise the sound-control abilities of the entire wall assembly.

Using resilient channels, for instance, to acoustically isolate gypsum board from wall studs, and thereby reduce sound transmission, has been a common sound control technique since the 1960s, but has created its share of problems on the job. These sound-dampening metal strips are screwed in perpendicular to studs, and the gypsum boards are carefully screwed into the resilient channels. This requires high precision, though—a simple mistake, such as installing the resilient channels too close together or upside down, can result in the creation of a new sound transmission path negatively impacting the assembly’s acoustical performance. This occurrence is referred to as a ‘short circuit.’ Interferences with resilient channel performance can also occur during picture-hanging or pressing of heavy objects against the wall. Investigations have found that resilient channels have a 90 per cent post-construction failure rate.

Building double-stud walls or installing multiple layers of gypsum board can also be effective, but this is often costly. As with resilient channels, incorrect placement of the boards can compromise the wall assembly’s noise-reducing abilities. Additionally, these wall assembly configurations often increase the footprint of the wall, which reduces the usable square footage of the floor plan. With Toronto condo prices averaging $382,070 and a typical townhouse in Greater Vancouver now costing $563,700, more efficient use of floor space can yield real estate rewards of several thousands of dollars.

Fortunately, the emergence of new technology has permitted building product manufacturers to introduce more practical, smarter options for sound control in wall assemblies. One better example is laminated-core, noise-reducing gypsum board.

Laminated-core, noise-reducing gypsum board
Intended as a replacement for some of the contemporary sound control methods on interior walls and ceilings in residential, commercial, or institutional applications, laminated-core, noise-reducing gypsum board is a single-panel product containing a viscoelastic polymer core applied between two specifically formulated thin layers of gypsum board. The final product ends up being 13 to 16 mm (1/2 to 5/8 in.) thick—the same as traditional gypsum board thicknesses. It can be ideal for new construction or renovations over both wood and steel framing.

One sizable advantage of laminated noise-reducing gypsum boards is their ability to dampen sound transmission. The polymer core acts as somewhat of a shock-absorber that dampens board vibrations and dissipates the sound energy into thermal energy. Additionally, the boards perform well acoustically over an extended range of frequencies, resulting in higher STC ratings for wall assemblies. Therefore, this type of gypsum board is a suitable acoustic solution to specify to meet STC code requirements without materials such as resilient channels and isolation clips, which require complex installation.

Risks associated with resilient channels and isolation clips are eliminated when laminated noise-reducing gypsum board is directly applied to framing, resulting in more consistent and predictable acoustical performance. However, the laminated core noise-reducing gypsum board can be used to achieve extra sound transmission control in wall assemblies where resilient channels or isolation clips are desired. In such cases, the material helps reduce the negative impact of any short circuits.

Offering the same level of sound control as traditional multi-layered gypsum systems in the form of a standard-sized laminated noise-reducing gypsum board allows project teams to build effective noise-reducing walls with less material and no special tools. Additionally, the project will gain valuable square footage, cut construction time, and reduce material and labour costs. Minimal use of material also means a more sustainable structure in line with today’s green building practices.

Assemblies utilizing a single layer of laminated core noise-reducing gypsum board have been tested and proven to meet or exceed the acoustic performance of assemblies using double layers of traditional gypsum board. The high-performance gypsum board is therefore quite effective in applications where acoustic management is needed to dampen sound energy and significantly improve sound attenuation through walls and ceilings.

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Specifying laminated core noise-reducing gypsum board and insulation
The first step in writing specifications for laminated core noise-reducing gypsum board, including noise-reducing fibreglass insulation in the cavity, is calculating the sound rating needed for the building’s wall assemblies and designing them accordingly.

In this process, the following options should be considered:

• thicknesses of 13 or 16 mm (1/2 or 5/8 in.) Type X;
• widths of 1.2 m (4 ft);
• lengths of 2.4 m (8 ft) or custom;
• tapered edges; and
• compliance with ASTM C1396, Standard Specification for Gypsum Board, and ASTM C1629, Standard Classification for Abuse-resistant Nondecorated Interior Gypsum Panel Products and Fiber-reinforced Cement Panels

The second step is to compare the laminated core noise-reducing gypsum board systems against other contemporary gypsum board systems. Online calculator tools have been developed for this very purpose. By inputting site-specific material and installation costs and collaborating with manufacturers’ field sales representatives, design professionals can determine a customized comparison of the cost per area for the wall assemblies.

The final step is to calculate the extra real estate rewards from thinner laminated gypsum walls. Again, a calculator tool can be used for this purpose. For example, using the most recent Toronto average condo price of $382,070 and a 93-m² (1000-sf) condo area, it is estimated an extra profit of $1800 and $1500 (for a total of $3200) are possible by using laminated core noise-reducing gypsum versus double layer 15.9-mm (5/8-in.) Type X and 12.5-mm (½-in.) resilient channels respectively. Financial savings will vary depending on the market where the analysis is based.

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Installers may follow traditional interior gypsum board application and finishing methods when working with laminated noise-reducing gypsum board, but with a little more attention to detail for better acoustic performance. For instance, the board layout should stagger joints from one side of the wall to the other. Next, sound-absorbent fibreglass batt insulation should be installed in wall cavities for higher STC ratings where needed. Again, resilient channels in this application are no longer needed to achieve performance except in very acoustically sensitive situations. However, it is appropriate to specify putty pads—tested per ASTM E90, Standard Test Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions and Elements—or acoustical sealant to seal off sound flanking paths, such as electrical outlets and switch cutouts.

Panels of noise-reducing gypsum board should be installed per Gypsum Association (GA)-216/ASTM C840, Application and Finishing of Gypsum Panels and the manufacturers’ application instructions. Best practices call for a 6-mm (1/4-in.) gap around all wall perimeter edges to allow for any movement. Installers can cut laminated noise-reducing gypsum boards as they would other gypsum board—by deeply scoring from both sides and snapping. However, cutting across a 1.2 m (4 ft) width may require use of a hand or power saw. An acoustical sealant should be specified to seal the perimeter gaps and wall penetrations per ASTM C919, Standard Practice for Use of Sealants in Acoustical Application.

Laminated core noise-reducing gypsum board may be finished, painted, or wallpapered using conventional techniques. GA-214, Recommended Levels of Gypsum Board Finish, should be referenced when specifying the level of finishing desired.

Sound flanking paths
As previously mentioned, sealing off sound flanking paths is an important step in achieving exemplary sound control from the wall assembly. It will become even more essential with the 2015 NBC’s recent introduction of the apparent sound transmission class (ASTC) rating. This rating provides a more comprehensive measure of sound transmission than STC. It takes sound flanking paths into consideration in addition to the sound transmission through walls, ceilings, and floors. The new edition of the code requires a minimum ASTC rating of greater than or equal to 47 for wall assemblies. More acoustic insights on the 2015 NBC will be provided as it is adopted by the provinces.

Flanking paths are typically cutouts or gaps in assemblies that allow the transmission of sound between two spaces. Any gap in an acoustical structure that leaks air will also leak sound and can render an otherwise effective sound barrier useless. Typical flanking paths include:

• joints between walls;
• ceilings/floors;
• other walls;
• poorly fitted, unsealed, or undercut doors and windows; and
• mechanical or electrical service fittings and openings.

The following tips will help project teams reduce sound flanking paths from penetrations in their
wall assemblies.

Doors
Hollow-core doors are poor sound blockers. When privacy and sound control are key considerations, doors should be solid wood or have insulated cores. They should also be gasketed to prevent sound from passing between the door and the jamb or sill.

Windows
Double-pane and/or storm windows reduce sound transmission, with the addition of weather stripping helping as well. Windows facing exterior noise sources should be small and minimal in number. Double-hung windows of the variety that can be tightly closed should be specified.

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Wiring and piping
Holes for wiring or conduit should be sealed or caulked. Cutouts for electrical outlet boxes should be made precisely so boxes will fit snugly. Installing electrical outlet boxes opposite each other on each side of a wall is not recommended; these should be staggered. In bathrooms on opposite sides of a wall, medicine cabinets should also be staggered.

Holes cut out for piping should be sealed with caulking. Merely stuffing the holes with insulation is not sufficient, as sound can easily pass through porous insulation. However, insulating the holes and then caulking over the insulation
can be effective.

Smarter sound control on projects
Laminated core noise-reducing gypsum boards provide a cost-effective solution to projects where sound control is a top priority. With STC ratings that meet or exceed the acoustical performance of traditional multi-board acoustical wall assemblies, assemblies with laminated noise-reducing gypsum boards reduce material use and are therefore quicker and easier to install and considered more sustainable.

Consolidating all these sound-dampening abilities into one board also conserves valuable floor space— an important consideration in the burgeoning real estate markets of today’s Canadian cities. As an added benefit, laminated noise-reducing gypsum boards also have a moisture- and mould-resistant face and back papers to ensure good indoor air quality (IAQ).

The results of this combination are smarter sound control project cost savings and optimal indoor environmental quality for the well-being of building occupants—a combination that should be included on all projects.

Robert Marshall, P Eng., BDS, LEED AP, is a building science manager for CertainTeed Gypsum Canada. He has been appointed by the National Research Council (NRC) to the Standing Committee on Energy Efficiency in Buildings. Marshall can be reached via e-mail at robert.marshall@saint-gobain.com[6].

Source URL: https://www.constructioncanada.net/implementing-smarter-sound-control-strategies/

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