Sound advice: Fenestration and acoustic solutions

by tanya_martins | November 5, 2024 8:35 am

By Lisa May

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Comfortable, quiet interiors benefit occupants’ wellness and productivity. With a greater understanding of noise and its impact on people’s health, there is a larger context for specifying the acoustic performance of curtain walls, windows, and other fenestration systems to promote quieter interiors.

A well-designed building envelope will provide the necessary sound attenuation while maintaining daylight and outside views without compromising energy efficiency, safety, or functionality.

Understanding noise and its impact

Some sounds are welcome; other sounds are not. Sounds perceived as noise are stressful and impact health and well-being. Noise can elevate heart rate and blood pressure, which causes hypertension. Even after five minutes of exposure to regular traffic noise, people exhibit these physical indicators and report fatigue and mental tension. In a continuously noisy environment, people can experience muscle cramps, dizziness, nausea, vomiting, increased levels of stress-related hormones, and mental changes, including impaired cognitive performance.

At quieter sound levels, noise also affects awareness, concentration, and creativity. This can lead to more errors and reduced productivity, information retention, and the ability to problem-solve. Having quiet spaces and managing unwanted sound is essential to calming the circulatory, respiratory, and nervous systems and, ultimately, to health and wellness.

Loud and sustained noise causes hearing loss by permanently damaging the nerve endings of the inner ear. This limits the ability to hear high-frequency sounds and understand speech, which significantly affects communication and engagement. It can also make it challenging to understand others and maintain relationships.

Occupational hearing loss is one of the most common work-related illnesses and is permanent. About one in eight people in the U.S. working population has hearing difficulty. Workers with hearing loss are more likely to be injured on the job.

According to the World Health Organization (WHO), more than 700 million people—or one in every 10 people—are forecast to have disabling hearing loss by 2050. Unaddressed hearing loss poses an annual global cost of $980 billion. This includes health sector costs (excluding the cost of hearing devices), educational support costs, loss of productivity, and societal costs.

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Meeting code and project-specific needs

The International Building Code (IBC), the U.S. Green Building Council’s LEED Green Rating System, and the International Institute of Well Building’s WELL Building Program note acoustic requirements to protect people’s hearing, health, safety, and well-being.

Along with the Centers for Disease Control and Prevention (CDC) and Occupational Safety and Health (OSHA), other federal agencies also provide standards and guidance to assess the exterior noise environment properly:

• American National Standards Institute (ANSI)
• Federal Aviation Administration (FAA)
• Federal Highway Administration (FHWA)
• U.S. Department of Housing and Urban Development (HUD)
• U.S. Environmental Protection Agency (EPA)

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In addition, local and state governments often set noise requirements as part of land use regulations and usually are considered the authorities having jurisdiction (AHJs). Two examples are New York City’s Department of Environmental Protection and the California Green Building Standards Code, Title 24, also known as CALGreen.

Complying with codes, guidelines, and project-specific requirements, manufacturers of curtain walls, storefronts, windows, and other fenestration types offer systems with high acoustic performance. Fenestration systems that mitigate exterior noise and maintain interior comfort have also become integral to supporting and achieving buildings’ sustainable and wellness goals and design strategies. Not only is this important in areas with high sound levels, such as near highways, railways, or airports, but also to specific project applications such as health care, educational, hospitality, and multifamily buildings.

Healthcare facilities

The importance of windows’ acoustic performance has increased for healthcare facilities designed to protect a patient’s privacy, accelerate the healing process, or offer peaceful respite. A noisy overnight hospital stay can slow recovery, increase the need for pain medication, and contribute to increased expenses. Noise also affects the medical staff and care team. A lapse in concentration can have life-or-death consequences if a mistake is made with a patient’s medication or treatment.

With respect to healthcare facilities, LEED v4.1 Building Design and Construction (BD+C) describes acoustic performance for speech privacy, acoustical comfort, and background and exterior noise management. It references compliance with the high acoustic requirements categorized and defined in the Facility Guidelines Institute’s (FGI) publication, Guidelines for Design and Construction of Hospitals, of Outpatient Facilities, and of Residential Health, Care, and Support Facilities. Starting in 2026, these three publications will be known collectively as the FGI Facility Code.

Educational facilities

Noise exposure can be detrimental to developing infants and children. In addition to noise being associated with low birth weight, hearing loss in children can impact their ability to learn and communicate, which can have negative repercussions throughout their lives regarding their education, socialization, and behaviors.

Acoustically comfortable learning environments for students also help with better concentration and comprehension, allowing for higher academic achievement. LEED v4 .1BD+C: Schools include exterior noise as part of their minimum acoustic performance requirements to provide classrooms that facilitate teacher-to-student and student-to-student communication through effective acoustic design.

Hospitality and multifamily

When noise keeps people from getting a good night’s rest, they often are irritable and distracted. People whose circadian sleep patterns are more acutely or chronically interrupted present a full range of health and wellness issues. Medical studies of people who habitually sleep no more than six hours per night show an association with obesity, diabetes, hypertension, cardiovascular disease, and stroke.

Protecting high-risk and vulnerable occupants, newly constructed residential buildings funded by the U.S. Department of Housing and Urban Development (HUD) must incorporate sound attenuation features within prescribed “Normally Unacceptable” noise zones.

To promote occupant comfort and well-being, minimal acoustic requirements for exterior windows and entrance doors are also detailed in LEED v4.1: Multifamily and Residential–Multifamily Core and Shell. These draft rating systems have been available to non-North American countries and are anticipated for release in the United States.

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Measuring sound transmission

Noise can affect occupants inside a building even when the fenestration systems are fixed or when operable windows and doors are closed. Airborne sound transmission occurs when sound waves pass through an opening, such as an open window or door, or a material, such as glass or metal.

The decibel (dB) is a logarithmic measure of sound pressure level. Since decibels are logarithmic, they cannot be added, subtracted, or multiplied with ordinary arithmetic. For example, a sound that is 10 dB louder than another is ten times more intense. Small differences of less than ±3 dB in sound pressure level or transmission loss are barely perceptible.

A-weighted decibels (dBA) are a scale for measuring noise. Noise is considered hazardous or loud when it reaches 85 dBA or higher. The National Institute for Occupational Safety and Health (NIOSH) Recommended Exposure Limit (REL) for occupational noise is 85 dBA averaged over an eight-hour workday. Workers exposed to noise at or above the NIOSH REL are at risk of developing significant hearing loss over their working lifetime.

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A typical conversational voice of 60 dBA can be heard by someone 1 m (3 ft) away. Sounds that are 85 dBA often require a raised voice to be heard by someone 1 m (3 ft) away. Equipment that can produce noise levels around 85 to 90 dBA includes lawnmowers, vacuums, and power tools.

As noise reaches 95 dBA or more, it is more likely someone must shout to be heard by someone 1 m (3 ft) away. Exposures that average 95 dBA or higher include ambulance sirens and large sporting events. Typical sound levels at construction sites are 100 dBA and around 120 dBA for operating heavy equipment.

The Occupational Safety and Health Administration (OSHA) requires employers to implement a hearing conservation program when worker noise exposure is equal to or greater than 85 dBA for an eight-hour exposure or, in the construction industry when exposures exceed 90 dBA for an eight-hour exposure.

Pitch or frequency is expressed in Hertz (Hz) or cycles per second. Normal human hearing can sense frequencies from about 20 Hz to 20,000 Hz. Sounds in the 20 to 500 Hz range are categorized as low-frequency sounds. Low-frequency noises carry much more energy than high-frequency sounds and are, therefore, more difficult to absorb. As a lightweight material, glass performs much better at higher frequencies. Be cautious if acoustic expectations for fenestration systems dictate a performance level for any frequencies below 1,000 Hz.

Transmission loss (TL) measures a material’s or assembly’s sound attenuation at a specific frequency. A TL curve is generated over the frequency range or spectrum the human ear perceives. When needed for project specifications, this TL curve is usually converted to a single-number rating, either Sound Transmission Class (STC) or Outdoor/Indoor Transmission Class (OITC).

Rating acoustic performance

STC and OITC are the two generally accepted metrics for evaluating and specifying the acoustic performance of fenestration systems. A higher number indicates higher performance for both measurements, but the two measurements cannot be compared without access to the underlying TL data.

STC is a single-number rating system for sound transmission, developed primarily to measure the typical interior noise spectrum between rooms through interior walls. Products are tested and rated in accordance with ASTM E90, Standard Test Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions and Elements, and ASTM E413, Classification for Rating Sound Insulation.

STC is the most commonly specified measure of acoustical performance. Normal speech can be understood through products with an STC rating of 25. Loud speech is audible but not understood through products with an STC of 35. Loud speech is only audible as a murmur through products with an STC of 40.

Even in the most stringent commercial project specifications, STCs of 48 or higher are considered past the point of diminishing returns for fenestration products and can be very expensive to achieve.

OITC is a single-number rating system for sound transmission, developed primarily to measure the typical exterior noise spectrum between outside and inside through the building envelope’s walls, windows, and doors. Products are tested and rated in accordance with ASTM E90 and ASTM E1332, Standard Classification for Rating Outdoor-Indoor Sound Attenuation.

OITC is predominantly a measure of low-frequency attenuation, as low-frequency sounds are generally the more prevalent sound sources in typical urban environments. Acoustical consultants determine required performance levels by starting from exterior sound intensity data. This complex process requires consideration of the noise source (rail versus vehicle traffic versus aircraft), time-weighted exposure averages, and attenuation due to distance. Interior occupancy plays a major part in determining the required OITC rating. The highest-performance commercial window systems achieve OITCs in the low 40s.

Be cautious when comparing acoustic test results, as variation can be considerable. Results for STC and OITC of similar specimens can vary by as much as 2 to 3 dBA due to inconsistent installation practices, varying temperature and humidity, size differences, and aspect ratio changes. Attachments and sealants used around the perimeter may provide unrepresentative damping. The specimen size, as well as the glass-to-frame ratio, also affect the sound transmission loss.

Helping standardize laboratory procedures, ASTM E 1425, Standard Practice for Determining the Acoustical Performance of Windows, Doors, Skylight, and Glazed Wall Systems, establishes the test methodology, specimen criteria, and classification rating system for determining acoustical performance levels of window, door, skylight, and glazed wall systems only. It does not deal with openings between such assemblies and adjacent construction.

Field test procedures for sound transmission also exist, and the field results can vary from the laboratory results by as much as five points due to installation accessories, sound flanking through adjacent building elements, interior noise sources, and other factors. Most project specifications differ between the lab and field test results.

For additional information on these acoustic performance ratings, please see AAMA 1801, Voluntary Specification for the Acoustical Rating of Exterior Windows, Doors, Skylights and Glazed Wall Sections, and AAMA TIR-A1, Sound Control for Fenestration Products, published by the Fenestration and Glazing Industry Alliance (FGIA).

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Improving acoustic performance

The acoustic performance of curtain walls, storefronts, windows, and other fenestration products can be enhanced by:

• Adjusting the size or aspect ratio
• Improving damping with laminated glass
• Increasing air space within the insulated glass unit (IGU)
• Adding glazing mass

Maintaining an air-tight assembly to reduce flanking noise is also critical, especially at high frequencies.

Size and aspect ratio

Large glass panels can vibrate at a higher amplitude than their smaller counterparts, causing a dip in the TL at the glass’s natural frequency. Square lites with an aspect ratio (height to width ratio) close to 1.0 are more prone to resonance than rectangular lites with aspect ratios of 1.5 or greater.

Results of previously tested glass-frame combinations should be reviewed in that context. Additional framing members added to reduce glass surface area may be sufficient to improve acoustic performance to targeted levels. The effects of size and aspect ratio are less pronounced when laminated glass is used.

Laminated glass

IGUs have two or more glass lites in a sealed unit to create double- or triple-pane glazing. Each glass lite within the IGU may be a different glass type or have various coatings to increase thermal performance and other qualities. Laminated glass lites are fabricated by bonding a polymer interlayer between two glass layers.

Laminated glass is often a cost-effective option for improving acoustic performance, with added safety and security advantages. Using laminated glass minimizes “coincidence”—a resonant frequency exhibited by rigidly supported glass lites. Resonances can be seen by increased sound transmission at a specific frequency or frequency range. Resonant frequency can sometimes be shifted out of the audible range by changing the size, thickness, and aspect ratio of glass lites.

Temperature can also affect the sound transmission loss of laminated glass panels. Fenestration systems containing laminated glass perform better in warm environments than cold ones since the interlayer’s damping characteristics improve at higher temperatures. Studies have shown that the STC and OITC ratings can change by up to five and three dBA, respectively, over a glass temperature range of 15 to 32 C (60 to 90 F).

Be aware that laminated glass fabricators publish acoustic data on “glass-only” prototypes based on testing loosely supported lites without framing. While somewhat useful for glass-to-glass comparison purposes, it is not recommended to use such results in project specifications, as any rigidly framed fenestration system’s STC or OITC test will be significantly lower.

Air space

An alternative to laminated glass involves increasing air space of IGUs through non-standard IGU spacers or interior access doors. In general, adding another layer of glass at the expense of air space does not help much, i.e. a 38 mm (1.5 in.) triple IGU will perform similarly to a 38 mm (1.5 in.) double IGU. Air and argon in the space of an IGU perform essentially the same. Depending on make-up, the practical limit on sealed IG air space width is 19 mm (0.75 in.) to 25 mm (1 in.).

Incremental changes in air space typically offer only marginal improvement in acoustic performance. In one side-by-side test of an IGU employing unequal glass thickness at the interior and exterior lite, increasing the air space from 13 mm (0.5 in.) to 25 mm (1 in.) improved STC by 1 dBA, with no change in reported OITC.

Thicker Glass

Typical system performance [6 mm (0.25 in.) minimum glass lite thickness] Where: IGUs = Insulating Glass Units STC = Sound Transmission Class OITC = Outdoor/Indoor Transmission Class
	STC Range	OITC Range
Windows using balanced IGUs without laminated glass	29 to 34	25 to 29
Windows using unbalanced IGUs without laminated glass	31 to 39	26 to 34
Windows using IGUs with one lite laminated	33 to 41	28 to 35
Dual-glazed systems with access doors	34 to 43	30 to 35
Triple-glazed systems with access door	41 to 48	32 to 40

Thicker glass

In general, the use of “unbalanced” IGUs—where the exterior and interior lite are of different thickness—improves both STC and OITC by reducing the effect of resonance. In one recent side-by-side test of an IGU employing unequal glass thickness at the interior and exterior lite, STC performance improved by 5 dBA and OITC by 3 dBA versus a balanced, symmetrical IGU. In this test, the outboard lite was increased from 6 mm (0.25 in.) to 8 mm (0.31 in.), a cost-effective performance improvement strategy.

Once options for unbalancing glass thickness have been exhausted, adding mass using significantly thicker glass can be the most expensive yet effective means of improving window/CW system acoustic performance. It should be considered only when previously mentioned options do not suffice. Depending on the application, thicker glass can have either a positive or negative effect on the coincidence effect and, therefore, acoustic performance.

Framing systems

The frame design makes little difference in acoustical performance for any given air-tight, rigidly supported glass-air space combination. As measured by low frequency-dominated OITC rating, acoustic performance is generally unaffected by framing mass, frame cavity insulation, the presence/absence of thermal breaks, vents, or glazing gasket design. Adding sound-absorbing foam between the lites of a dual-glazed system can improve STC 1 to 2 points, but only when deficiencies are predominantly in frequencies above 1,000 Hz, and OITC typically is unaffected.

Verifying acoustic compliance

Unlike thermal performance, no commercially available computer modeling tools can accurately predict acoustical performance. For project estimating purposes, the specifier should accept existing acoustic performance test reports as proof of compliance for previously tested glass-frame combinations, even if results or exact compositions vary to a small degree.

Since no fenestration system manufacturer could practically pre-test every possible glass-frame combination for a broad product offering, provisions should be made for job-specific acoustic testing or evaluation of existing test reports by acoustical consultants. The complex physics associated with multi-layer fenestration systems of different sizes, containing many materials and complex three-dimensional geometries, makes an empirical approach necessary when required performance is compared with past test results.

To make acoustic performance guarantees relative to future job-specific test results, manufacturers can be forced into expensive overdesign. Such guarantees are not in the project’s best interests. Working together early on, the design professional, specifier, acoustical consultant, and manufacturer can select or design the right product for the project’s needs.

As a final note, check that acoustical performance requirements are written in clear, technically valid language, preferably citing STC or OITC, and that the glass descriptions in the glazing section of the specification match the acoustical requirements of the appropriate fenestration product section, such as Curtain Wall and Glazed Assemblies, Storefronts and Entrances, or Metal Windows. Contact an experienced fenestration system manufacturer for additional support regarding product performance, selection criteria, and evaluation considerations.

Thicker Glass

Typical system performance [6 mm (0.25 in.) minimum glass lite thickness] Where: IGUs = Insulating Glass Units STC = Sound Transmission Class OITC = Outdoor/Indoor Transmission Class
	STC Range	OITC Range
Windows using balanced IGUs without laminated glass	29 to 34	25 to 29
Windows using unbalanced IGUs without laminated glass	31 to 39	26 to 34
Windows using IGUs with one lite laminated	33 to 41	28 to 35
Dual-glazed systems with access doors	34 to 43	30 to 35
Triple-glazed systems with access door	41 to 48	32 to 40

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Author

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Lisa May is director of preconstruction and architectural services for EFCO, Tubelite, and Alumicor brands. She is an active member of the Fenestration and Glazing Industry Alliance (FGIA), participating in several committees. She works closely with architects, specifications professionals, building owners, and consultants across the United States and Canada. For 25 years, May has assisted with fenestration and framing product selections, performance-based specifications, and pre-construction needs for commercial and institutional building projects. She can be reached at lmay@apog.com

Source URL: https://www.constructionspecifier.com/acoustic-optimized-building-envelopes-wellness-productivity/

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