While healthcare professionals are on the frontlines of delivering care and comfort, architects and contractors are essential workers when it comes to mitigating an enduring pain point in the healthcare setting – flanking noise.
Whether flanking noise comes from HVAC equipment on a hospital’s rooftop, transmits between walls in assisted living units, or complicates communication in a telemedicine practice, optimizing acoustics is integral to a comfortable environment for patients, care providers, staff and visitors. And at a time when hospital reimbursements are aligned with patient satisfaction, noise management is fundamental to business performance.
The walls, floors, and ceilings of a healthcare facility can all act as proxy sound speakers. The increased use of hard surfaces to reduce infection pressure coupled with decreased use of carpet, drapes and other sound absorbing textiles creates an environment conducive to sound carrying over between walls, floors, and ceilings. Vibrations from mechanical equipment ranging from rooftop HVAC systems to water pipes present still more challenges to acoustic performance in the healthcare setting.
Managing flanking noise
Sound is stealth and opportunistic. A gap of just 1/32 of an inch between a floor and a wall presents easy access for sound to carry over. Noise will always seek the path of least resistance. Flanking noise refers to sound that travels around walls and floors as well as sound that flows through adjacent junctions and openings. Managing flanking noise becomes especially important in higher performing walls – particularly those with a sound class transmission (STC) of C45 and higher. For walls with STCs below STC/llC45, most common noise control practices are very effective.
While STC provides a measure of energy lost as it passes through a wall and Outside In Transmission Class (OITC) provides a measure of sound transmission through exterior walls, these evaluations should not be confused with the Noise Reduction Coefficient (NRC) which measures how well a material is able to absorb sound – including flanking noise – regardless of the wall assembly and its STC. Typical NRCs are in the .4 to 1.2 range and a material’s NRC will provide a reliable indicator of the material’s noise absorption.
Sealing the perimeters of patient rooms helps defend against flanking nose. The use of acoustic caulking between the floor and the wall can help mitigate sound noise. Adding a resilient channel can also help improve sound insulation of drywall, sheetrock, plasterboard, walls, and ceiling assemblies. The resilient channel acts to isolate the drywall from the framing studwork, weakening the sound wave through the assembly and reducing noise. Floating the floor with a truss can help to reduce the flow of sound across structural paths.
Four approaches to managing flanking noise
Designers generally follow four approaches when dealing with flanking noise: absorbing sound, blocking sound, breaking sound, or isolating sound.
Absorption: As the name implies, sound absorption techniques are designed to capture sound energy/vibrations and trap the noise. Some options include adding insulation baffles on the ceiling, applying decorative panels on the wall, or introducing acoustic blankets behind wall elements to capture sound.
Blocking: By creating a barrier, insulation installed in the wall cavity can block waves of sound energy from transmitting through the assembly. A common question is whether mineral wool or fiberglass provides a more effective insulating material. For basic walls, there is no significant difference between the two insulations. However, designers should consider what other properties may be desirable for the insulation to support. For example, the innate fire resistance of mineral wool may make it a preferred material to support life safety objectives. Performance properties such as a material’s ability to manage moisture (both vapor and liquid) or its ease of installation are other factors that may drive insulating material choice.
Breaking: A particularly effective tool for mitigating noise, breaking disrupts the path for sound to travel – i.e. placing insulation in the cavity between two stud walls interrupts the sound flow and absorbs the noise, reducing its flow from the first wall space into the second space. This method of mitigating sound is popular in multi-family environments and can work well in residential health care spaces such as assisted living or senior healthcare communities.
Isolation: A fourth approach for dealing with flanking noise is isolation. Isolating sound is a common approach for dealing with mechanical noise such as HVAC equipment. This approach relies on a separation of the soft connections between system components. Resilient channels can reduce the transmission of noise through studs and across the cavity path, allowing for a mechanical connection between systems but impeding the conduit of vibrations such as those coming from mechanical systems. For example, adding vibration insulators underneath a cooling unit can keep impact noise from transmitting down to underlying areas. Similarly, soundproofing clips in the wall can isolate vibrations in one area as can acoustic floormats. When resilient channels and absorption techniques work together, it is possible to achieve dramatic improvements in sound transmission and noise control.
Design tips for sound management
Whether noise is managed via absorption, blocking, breaking, isolation or some combination of all four, good design remains the first strategy designers should turn to when seeking to reduce flanking noise. Following are some tips to consider in the design phase to help manage flanking noise.
Consider the function served: Consider the function of a space and its traffic levels. Isolate areas with heavier activity, such as nurse stations, away from consult areas where privacy and clear communication are critical.
Prioritize privacy: Position patient room doorways so they are not directly across from each other to help protect both speech privacy and visual privacy. As hospitals are home to some of life’s most important conversations, speech privacy is critical. Locate waiting areas away from consultation rooms. While sound masking should not be viewed as a panacea for managing acoustics, it may resolve some design challenges particularly in retrofit designs.
Look for low-cost retrofits: Target interventions that are easy to introduce – for example adding drop down door seals helps manage flanking noise without incurring major expense. Installing insulation batts above the ceiling for walls that do not extend to deck, will generally improve privacy at a much lower price point compared to replacing/retrofitting ducts or walls.
Choose full-height walls: Full-height wall partitions that extend up to the ceiling deck are the best defense against noise traveling from room to room via open space above the ceiling. When a full-height wall partition is not practical, installing a row of insulation 6 inches thick and 24 inches wide along the perimeter of each wall above the ceiling can help mitigate sound transmission. Installing crown molding at the intersection of wall and ceiling is another design tactic to help reduce flanking noise.
Consider mechanical spaces and line ducts: The phrase “the pipes are coming up” is a common observation in mechanical areas. Beyond providing thermal and moisture protection and defending against corrosion under insulation, fibrous pipe insulation provides protection against noise radiating through the pipe. Adding insulation to the wall assembly of the mechanical room and surrounding area can help keep pipe noise from infiltrating other areas of the hospital.
Properly installation of piping and appropriate flex duct and duct liner help mitigate noise from hospitals’ HVAC systems. Some Owens Corning duct liner products include an EPA registered biocide to help protect the airstream surface from microbial growth while also absorbing fan and turbulence noise from mechanical systems.
Technology demands acoustic quality: The recent pandemic has shone the spotlight on the growing use of telemedicine. Technology – whether a phone or video call – can compromise how well noise carries. Conventional approaches to masking sound, such as white noise, can disrupt audio quality in the telemedicine space. Early design consideration and the inclusion of passive acoustic elements such as fibrous acoustic panels and other sound absorbing materials can support audio quality in telemedicine spaces as well as makeshift environments when additional capacity may be required at a moment’s notice.
Leverage FGI guidelines: Finally, designers should leverage guidelines to help support acoustic decisions. In the U.S., the Facility Guidelines Institute (FGI) maintains and works to elevate acoustic recommendations for healthcare facilities. FGI guidelines were updated in 2018.
When it comes to managing flanking noise in the healthcare environment, sound management and sound performance are interconnected. Sound planning and design at the out-start can achieve a more comfortable environment for patients, caregivers, and staff.
Owens Corning invests in research to improve the acoustic performance of walls assemblies via new innovations. For example, researchers recently evaluated 296 walls to identify key variables that influence sound performance and studied the impact of new lightweight drywall options, stud types, varied insulation options, and configurations on sound performance. On the mechanical side, a study tested 18 pipe insulation combinations including various jacketing materials, the combination of FOAMGLAS® cellular glass insulation with mineral wool and layering of mass loaded vinyl materials.
Kevin Herreman is manager of acoustic programs at Owens Corning.