Post-occupancy evaluations conducted by the Center for the Built Environment (CBE) in America reveal that green building acoustics are typically worse than their traditional counterparts, and that over half of respondents feel noise inhibits their work.
Although there is agreement that this can be the case without appropriate design, there is also the potential for them to become far better acoustically.
According to the CBE, some of the areas that suffer in particular from an acoustic perspective include buildings with an open ceiling, as well as buildings with designs for maximising daylighting, so that spaces are narrow and reflect sound more.
Matthew Verth from Resonate Acoustics says the potential acoustic defect here is less about geometry and more about removing a ceiling that traditionally provides sound absorption with no mitigation provided in lieu of the "missing" ceiling.
“One possible solution is the installation of acoustic absorption on the underside of the soffit, although this may interfere with the need for exposed thermal mass if this strategy is employed," Verth said. "Another option is a perforated metal pan ceiling which would permit chilled beam cooling to be employed. However to work effectively as an absorber a metal pan ceiling often requires an acoustic backing to provide reasonable absorption values, or an acoustic pad to improve transmission loss to control in-ceiling noisy items and/or room to room noise control.”
“The absent ceiling often means that any noisy items left in the ceiling - and there are always a few fans and fan coil units - must be acoustically treated by boxing-in or wrapping.”
Sandy Marshall from acoustic consultants Marshall Day says having an open ceiling – in other words, exposed slab and services – does not necessarily have to be detrimental to the acoustics of an open plan office area.
“The ceiling is the most efficient location to place acoustic absorption within an open plan office to assist with reverberant noise control. The requirement for this typical design inclusion largely depends on how the space is used by the occupants,” said Marshall. “Where open ceilings are part of the design or narrow spaces are used to maximise the use of daylight, the acoustic consultant and architect need to work together to find an appropriate solution to achieve the architectural and acoustic requirements within the sustainable design constraints.”
Alternative solutions may also include:
- The use of spray-on absorptive products applied to the ceiling slab which can be painted as per the architects or interior designer's requirement
- Careful placement of absorption such as suspended panels over critical areas
- The use of absorptive furniture such as pin boards placed carefully to minimise reflections
- The use of diffusive panels to scatter undesirable reflections
The CBE reports also states that the background sound level in most conventional offices is already too low. The use of high-efficiency heating and cooling systems means that it is generally even lower in green buildings.
“In our experience, if building services noise is too quiet, disturbance due to speech increases and occupants believe the building to be too 'noisy' as a result,” said Verth.
“When noise levels fall below the satisfactory levels, speech privacy is therefore more likely to be compromised and become a potential problem in office fit outs,” added Marshall
Solutions for this issue can include increasing the sound insulation ratings of partitions between offices or increasing the background noise level by other means, such as a speech masking system, which produces a broadband noise not dissimilar to noise from air conditioning to increase background noise levels where they are considered too low.
Beyond the CBE survey, other recent North American studies of user satisfaction in green buildings have offered a range of assessment outcomes for acoustic issues.
A 2009 Canadian paper noted that “a clear trend exists with a decrease in acoustic satisfaction associated with green buildings." However, a subsequent 2013 Canadian study found that this decrease in acoustic satisfaction might be a logical consequence of the prevailing LEED credit scheme, which offered credits for building design features such as low partitions to allow daylight to penetrate and allow views, and hard ceilings and floors to improve air quality. However, both these features have negative effects for acoustics (Bradley & Wang, 2001). This is compounded by the fact that no credits for acoustic performance existed.
Marshall says an important distinction in Australia is that most AGBC green rating tools include acoustic (Indoor Environment Quality or IEQ) criteria.
“While the criteria by no means guarantee a suitable acoustic outcome for a building, it may well result in an improved acoustic outcome compared to a building assessed without the acoustic criteria,” she said
The Pixel Building in Melbourne is proof that green buildings don’t need to suffer acoustically. It scored a perfect 100 points under the Green Building Council of Australia (GBCA) Green Star - Office Design and As Built v3 Technical Manual, including both points available under the IEQ-12, Internal Noise Levels category.
“The site is exposed to moderate levels of traffic noise and a double glazing system was developed to maximise sound insulation performance and meet the required thermal rating. Air-conditioning is provided via an under-floor air distribution system requiring careful balancing,” explained Marshall, who worked on the acoustic designs. “Other acoustic design challenges involved with the development included addressing noise from the operation of vacuum toilets and roof mounted plant including wind turbines."
'Exposed soffits are integral to the thermal performance of the building, which limited the available areas for sound absorptive treatment. Sound absorptive treatments have been specified to available wall areas and integrated within workstations.”
Unsurprisingly, Verth believes that ultimately good input from an experienced acoustic engineer can avoid these problems.
He suggests the following key points be considered:
- Early acoustic involvement to locate acoustically dissimilar spaces in sympathetic locations
- Establish an acoustic needs brief
- Acoustically improved enclosed spaces so that people are inclined to use them for private conversations (leaving the open plan area 'less disturbed' )
- Properly designed and installed sound masking in lieu of traditional HVAC noise
- Other acoustic absorption in lieu of 'missing' acoustic ceiling tiles
- Good use of acoustic absorption in and around noisy areas
- Areas that feature conference call facilities
- And not describing noise disturbance as collaboration