The Science of Sound: Building Science Experts Reveal
Common Pitfalls in CRE Environments
This is the second of our Unintended Consequences of Sound series covering acoustic comfort for CRE properties and projects, a subject that has risen in importance in the COVID-19 ‘working from home’ era.
In our first article in the series, Saint-Gobain experts Stan Gatland, Manager of Building Science Technology, and Lucas Hamilton, Manager Applied Building Science, shared insights into the science of sound in the built environment. These savvy building science experts reveal the pitfalls of commercial building design to help owners and developers be savvier in their understanding of the outcomes, experiences, and ultimately the value of their buildings.
Building owners must accommodate the aesthetic aspirations of a building with acoustic comfort. Unlike visual design, you can’t “see” sound on architectural drawings or renderings, so finding the proper balance is a complex challenge that involves art, science, and careful planning. In most instances, achieving the look and feel an owner desires requires the expertise of building scientists with decades of field experience.
Overlaid on top of those emerging 2020 trends is a shift that has occurred over the past several years to blend a mix of uses at projects. These mixed-use developments may be smart from a land use perspective, with amenities that appeal to demographic demand, yet absent a skilled building science expert to guide a holistic design the various sounds can become a chorus of competing noises.
Amenities may draw tenants to a project, but they also create more value-damaging noise. It adds up to sound sources that must be accounted for in order to create appealing and pleasing spaces that occupants are willing to pay for year over year.
“Acoustic comfort is a tenant expectation and differentiator today,” said Gatland. “But that often runs opposite of the host of retail and entertainment activities now common at office and multi-family properties alike. That could encompass cooking classes, a dry cleaning/laundry service, package delivery management, personal shoppers, pet groomers, a rock-climbing wall, a spa/massage center, a community wine cellar, or classes for yoga, aerobics, or wellness.”
Each of those elements create different sounds that may impact the surrounding space or neighboring sites intended to be a quiet or relaxing component of the property.
Eye-Catching Designs Must Also Be Pleasing to the Ear
The trend toward all-glass buildings has improved visual comfort, yet the unintended consequences of that design can play havoc with acoustic comfort.
As a hard sound-reflective surface, glass creates acoustically reverberant spaces. Therefore, without the right combination of acoustical solutions, a visually pleasing design can lead to an aurally uncomfortable space that acts like an echo chamber.
Since large open spaces such as commercial offices, classrooms, restaurants, and retail environments frequently incorporate reverberant design elements like expansive glass facades, smooth finished wall surfaces, hard floors, and industrial-style ceilings, they must have both an aesthetic and functional appeal to achieve true comfort and harmony.
“Those finishes all have a limited ability to absorb sound energy and dampen sound reflections,” said Hamilton. “Buildings designed with an emphasis on visual comfort must consider a combination of solutions to achieve the desired acoustic comfort outcomes.”
There are four goals that building scientists such as Gatland and Hamilton say help provide a superior acoustic environment:
1. Reducing sound reverberation time (echo factor)
2. Limiting airborne noise (sound transmission from space to space)
3. Reducing impact noise
4. Minimizing background noise
Reducing Sound Reverberation
The reduction of sound reverberation time is accomplished by employing sound- absorbing surfaces such as fabrics, carpeting, and acoustical ceilings or wall panels. The best plan is to configure those spaces to reduce, rather than reflect, the sound energy.
Limiting Airborne Noise
When limiting airborne noise, one important consideration is to design high sound transmission class (STC) assemblies. STC is a laboratory measurement used to study the resistance of a wall, ceiling, or floor to the passage of sound. The higher the STC number, the more the sound is deadened. This can be accomplished by enclosing or separating spaces with acoustically efficient walls.
Reducing Impact Noise
To reduce the transmission of impact noise, high-impact insulation class (IIC) assemblies are often used. Methods include isolation of finished floors and ceilings with resilient underlayments, installing sound-absorptive floor coverings (carpets and carpet pads), and choosing ceiling suspension systems that include sound-absorbing cavity insulation.
Minimizing Background Noise
To eliminate the droning of mechanical equipment, employ vibration dampening techniques and high sound transmission-reducing enclosures. Set up HVAC systems that absorb noise that would otherwise transmit through the ductwork. You can also mask background noise in a space with sound by adding white noise or background music.
Building science experts advise the solutions to acoustic comfort requires addressing the sounds in open, collaborative, and transition spaces. That means adding acoustically absorptive surfaces where possible, such as ceiling systems, wall panels, furniture, carpeting, or plants.
“It is wise to consider, ‘What’s the desired acoustic comfort outcome?’,” said Hamilton. “Classrooms require excellent speech intelligibility. A healthcare facility requires high levels of speech privacy in patient rooms. Commercial offices and restaurants seek good speech intelligibility at individual workstations and dining tables, which drops off over short distances to increase privacy and limit distractions to others.”
An example of how targets for a high-performance building can result in disastrous acoustic outcomes occurred at a community center in central California, where the lack of sound absorption in a design created conditions for occupant discomfort.
The customer desired a very quiet space during the morning for the center’s programs and activities, but that expectation ran counter to reality when the occupants heard disturbingly loud popping noises every morning as the sun rose. Ultimately, the roof system and the center’s acoustical design were identified as the culprits.
In order to meet the demanding energy efficiency targets and local seismic and fire codes, the community center’s metal roof deck was highly insulated with rigid, polyisocyanurate foam insulation board. Unfortunately, when the morning sun hit the structure, the roof deck surfaces did not heat up at the same time. The linear thermal expansion differences within materials and between components caused friction that generated the loud popping noise. The noise transmitted easily because of the roof assembly being acoustically transparent and reflective.
Further compounding the noise problem was the aesthetic and functional design of the center’s large, open spaces, which offered limited acoustical absorption due to the abundance of smooth, bright clean surfaces specified to maximize the spread of natural light though the building.
Improving the acoustic comfort experience at the building required the addition of substantial absorption at the underside of roof deck. Though there are many aesthetically pleasing solutions available to consider, it is always worth the financial investment to address acoustics up front versus the expense of fixing the problems after occupancy.
Overhead Sound Threats
“As a result of eons of evolution, humans perceive overhead disturbances as a threat,” said Hamilton. “The modern built environment has only been in existence for recent centuries of civilization, thus reflected or transmitted sounds found in buildings are relatively new to the evolutionary experience of the human species. Sounds from above become an instinctual life safety issue, and that’s why acoustics are so important in the built world .”
Examples of the way overhead sound can be mitigated in multi-family buildings can be found in the construction methods used. A common situation is when the neighbors above a space have hard floors. A builder or developer may increase the fire and sound control between individual units by installing a lightweight concrete slab on top of wood framed floor-ceiling assembly, but this may open the door to other unintended (and especially noisy) consequences.
In the case of a high-end residential project, many luxury homeowners want hardwood and tile floors. These, as well as ceiling mounted recessed lights and loudspeakers, can create issues of unwanted disturbances for neighbors when sounds like loud footsteps, dropped items, and the dragging of furniture are transmitted directly to the space below.
“Ideally, the finished ceiling would be structurally isolated and disconnected from the supporting structure using a combination of a resilient drywall suspension system backed with fiberglass insulation, and by acoustically sealing all penetrations and the perimeter,” said Gatland.
When existing floor support structures, ceiling height, and fire sprinkler systems limit solution options, a developer can help soften the sound by disconnecting the floor structure of the upper unit from the ceiling structure in the lower space.
Solving issues before they become problems is just one area in which Saint-Gobain delivers the value of building science. By discovering the pitfalls and unintended consequences of deficient design, we help property owners avoid the need for costly change orders or post-occupancy renovations.