by Heather Evans
Acoustic performance has become an increasingly vital consideration in the construction industry due to population growth, rapid urbanization, and the ongoing research making connections between noise exposure and the health of building occupants.
The Environmental Protection Agency (EPA) has reported, noise pollution negatively impacts millions of people and leads to many problems such as “stress-related illnesses, high blood pressure, speech interference, hearing loss, sleep disruption, and lost productivity.” According to the Centers for Disease Control and Prevention (CDC), one in four adults show signs of noise-induced hearing loss. Occupant well-being and comfort are, therefore, a critical component in new construction. There has also been a boost in retrofitting commercial spaces, homes, and schools for acoustic performance, such as those located near airports and major thoroughfares.
As the construction market continues to thrive, the industry has an opportunity to make a positive impact on human health and comfort by propelling acoustic performance forward. Moving ahead, it will be critical to focus on acoustics of exterior façades in the development of new construction and retrofit projects.
Noise level risks and recommendations
Noise exposure can negatively affect the physical and mental well-being of humans in numerous ways. These effects can show up in homes, schools, and workplaces. For example, relaxation and sleep is greatly affected by exposure to certain types of noise. Further, the ability to concentrate on tasks or listen to a conference call in the workplace can often be impacted by outside sounds.
The World Health Organization (WHO) reports, “Chronic noise exposure in classrooms can impede academic performance in areas such as reading ability, comprehension, short- and long-term memory, and motivation. On average, children who are exposed to noisy learning environments have lower assessment scores on standardized tests.”
For reference, WHO recommends less than 30 dB in bedrooms for quality sleep, and less than 35 dB in classrooms for optimal learning. A pamphlet released by the New York City health department shows that:
- a whisper is 30 dB;
- normal conversation is 50 to 65 dB;
- midtown traffic is 70 to 85 dB; and
- a nearby jet is 130 dB.
WHO reports very similar numbers, and also includes information on safe listening levels and duration of noise exposure.
Essentially, “the total amount of sound energy to which an individual can safely be exposed remains constant: the sound energy of lower volumes listened to over long periods of time is the same as that of louder sounds heard over a short period.” For example, exposure to 85 dB should be limited to less than eight hours per day and only nine seconds for 120 dB.
Since many homes, schools, offices, hotels, churches, and other buildings are situated near airports, railways, street traffic, and other constant/loud exterior noise, it is evident many people are being exposed to unsafe sound levels on a daily and nightly basis.
How cities are responding
New York City and Chicago are aggressively addressing noise pollution and its effects on human health. In Chicago, the O’Hare Residential Sound Insulation Program (RSIP) was created to reduce the impact of noise on homes near the airport, and the O’Hare School Sound Insulation Program (SSIP) addresses noise levels in nearby schools. These programs work to install sound insulation in homes and schools impacted by aircraft noise. For example, by incorporating acoustical insulation batts in ceiling assemblies, installing new air-conditioning and ventilation systems, and weather-stripping windows and doors, as well as adding vestibules at exterior doors, they were able to mitigate noise in schools.
In New York City, about one in six adults report ringing in their ears or hearing loss. According to the NYC health department, a 2012 study found there are many outdoor spaces in the city where noise levels are higher than is considered safe for public health. The NYC department of environmental protection (DEP) has created the NYC Noise Code, which lays out restrictions on city noise and decibel levels impacting comfort and safety, such as noise from construction, air-conditioner units, rooftop circulation devices, food trucks, and motor vehicles. For example, every construction site must have a noise mitigation plan prior to the start of work and the use of vehicle horns is illegal, except as a warning in situations of imminent danger.
Understanding STC versus OITC
The construction industry is seeing a growing number of façade innovations designed to improve acoustic comfort. It is critical to understand acoustic ratings to ensure proper product selection, installation, and desired outcome. It is first important to know the difference between sound transmission class (STC) and outdoor-indoor transmission class (OITC) ratings. STC specifies noise transmission from room to room and OITC deals with transfer of sound from outside to inside. The STC rating has been around for decades and is often relied on for soundproofing a building. Established in the 1990s, the OITC rating is newer to the industry and often overlooked.
While both are effective, it is important to apply ratings to the right scenarios in order to provide the highest level of occupant comfort. An STC rating is sufficient for soundproofing walls between offices, hotel rooms, or condo units, while OITC is necessary for commercial buildings in close proximity to an airport, or in the midst of an urban core.
Additionally, it is important to understand the frequency of the noise that should be dampened (i.e. air traffic [lower frequencies] or train/subway noise [higher frequencies]). A product may have a high STC or OITC rating, but struggle with the frequency that needs to be dampened. Product test results are a great way to evaluate this piece of the acoustic puzzle. When a product is tested according to ASTM E90, Standard Test Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions and Elements, and serves as part of the American Architectural Manufacturers Association (AAMA) 1801, Voluntary Specification for the Acoustical Rating of Exterior Windows, Doors, Skylights and Glazed Wall Sections, protocol, the transmission loss is recorded in multiple frequencies, as the entire sound spectrum is checked, which helps to pinpoint performance based on the surrounding environment. Knowing and understanding the frequency one is dealing with ensures the best product match.
Another critical factor specifiers should understand when setting requirements for product performance is human perception to decibel level changes, as it can greatly impact occupant comfort. For instance:
- +/– 3 dB is barely perceptible;
- +/– 5 dB is clearly perceptible; and
- +/– 10 dB is perceived as double or half noise level. Also, nighttime ambient noise is 10 dB lower than daytime.