Soothing Sounds of Sustainability
August, 2010

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Green Office Space Brings Acoustical Challenges

By Niklas Moeller

The sensory environment influences the ability to concentrate. Disruptive noises and conversations can make tasks more difficult to complete and increase the likelihood of making errors.
   
Such factors have been one of pitfalls of so-called green workplaces. Post occupancy evaluations conducted by the Center for the Built Environment reveal that the lack of privacy and the detrimental effect of noise on performance are among top complaints from green building occupants.

A 2004 study of several Canadian buildings pursuing LEED® credits for natural ventilation, open plan and low energy use shows that poor acoustics can make even the greenest spaces less desirable. These facilities were found to be unacceptable, acoustically speaking, and had to be renovated at great cost.

Measures are available to address privacy and noise control after tenants have moved into the space, but it is advisable to set goals and determine how they will be achieved during the design stage. Acoustic professionals typically follow a formula known as the ABC Rule, which stands for absorb, block and cover. Although it can be challenging to apply these strategies in the context of sustainable design, their positive impact on workplace satisfaction and productivity is certainly worth the effort.

ABSORB

Absorptive materials reduce the volume of noises reflected back into the space, the length of time they last and the distances over which they will travel. The ceiling is typically the most significant source of absorption in a facility. However, many green buildings feature an exposed deck to assist with temperature regulation and day lighting. This hard surface also allows sounds and conversations to echo, overlap, linger and travel greater distances.

Ideally, open spaces should feature a ceiling tile with at least a 0.75 Noise Reduction Coefficient. Tiles used in closed spaces should have a high Ceiling Attenuation Class, because they will be better at containing sounds.

Adding absorptive panels to 30% of the deck can mute some of the impact. Vertical baffles are another option.

In designs featuring an open ceiling, a perforated and corrugated metal deck can be used. In such cases, absorptive material would be placed behind the perforations before the concrete is poured.

Workstation panels should also be absorptive – at least on the inside, above the work surface – in order to reduce the volume of the occupant’s voice before it is reflected into the space. If the space is shallow to promote natural light penetration, absorptive panels should also be used on the walls to prevent sounds from ricocheting between the exterior wall and core.

Soft flooring should be used to reduce footfall noise. Designers can now choose products that contain a reduced amount of chemicals and/or recycled content, or are made from natural materials.

BLOCK

Walls, windows, doors and other physical structures act to block noise, but green buildings generally feature an even larger percentage of open-plan area than traditional counterparts. Thus, the height of workstation panels becomes essential in these spaces.

Panels should extend beyond the occupant’s seated head height (150 to 165 centimetres) or they will do little more than hold up the desks. Where natural light penetration is a concern, designers can compromise by using absorptive panels to a 120-cm height and top them with 30 cm of glass or another transparent material. They should ensure that the panels have a high Sound Transmission Class and that they are well-sealed along any joints, with no significant opens between or below them.

Many green designs use movable walls to create private offices and meeting rooms, but these walls may not provide a sufficient level of sound isolation between adjoining spaces. Gaps along the ceiling, exterior walls and floor should be addressed during installation. A good septum on each side of the wall is also advisable to prevent sound leakage along any cable raceways.

COVER

The final step of the ABC Rule uses background sound level to cover speech and noise. Green buildings’ use of natural ventilation and/or other advanced technologies that reduce noise associated with mechanical and forced-air also reduces the background sound level that can aid concentration in older office buildings. Conversations and noises are easier to hear and travel over even longer distances.

Open windows for air circulation are also open to disruptive exterior sounds. Meanwhile, green buildings with differing design and ventilation strategies between the exterior and core can suffer from variable acoustic conditions across the space.

A sound masking system can be used to replenish the background sound level and maintain it at an appropriate volume, which is typically between 42 and 48 decibels in commercial interiors. This type of system consists of a series of loudspeakers that are usually installed in a grid-like pattern above the suspended tiles or in an open ceiling. The sound they distribute is continuous and has been specifically engineered to increase privacy.

Masking mutes or reduces the impact of intermittent noises by decreasing the amount of change between the baseline and peak volumes to improve overall acoustical comfort. A networked masking system gives occupants the flexibility to adjust the set-up if the ambience changes in a specific area. Some sound masking systems provide paging and music distribution, eliminating installation and operating costs for a second system.

GREEN CONSIDERATIONS

Facilities managers may want to consider some factors: 

• Energy consumption. Ask how much power the system will consume. Most use less than that of a typical light bulb to cover 13,500 square feet.
• Environmental programs. Find out if the manufacturer adheres to programs such as the Restriction of Hazardous Substances (RoHS) initiative, which ensures that products meet requirements for low levels of heavy metals such as lead and cadmium.
• Lifecycle and maintenance. Most masking systems have a long lifespan and can easily be expanded or relocated. Networked sound masking systems can be reconfigured using a control panel or software, reducing churn costs.
• Recycling program. Check if the manufacturer offers a recycling program for end-of-life products.

Sound masking offers a solution that will allow building owners, managers and occupants to take advantage of the positive aspects of green buildings, such as improved indoor air quality, without detracting from the quality of the working environment. In open areas, masking increases the external-internal noise isolation, as well as that between workplaces. Masking can also reduce material costs by influencing wall construction standards and making movable walls feasible, contributing to the overall flexibility of the space and reducing waste generated from future renovations.

Niklas Moeller is Vice President of K.R. Moeller Associates Ltd., a global developer and manufacturer of the sound masking system, LogiSon Acoustic Network.