Blocking exterior sound to reduce noise pollution

What is exterior noise intrusion? Let's get started with the basics

Managing noise from the exterior is a constant challenge for design professionals. In the built environment, noise, by definition, is any unpleasant or unwanted sound. Noise can come from myriad sources, just as when we looked at managing interior sound in our last article. External noise on the other hand, such as road traffic, aircraft, or even neighboring occupants are just a few examples of noise pollution (often referred to as environmental noise) and should be considered during the design phase of a project.

Increasingly, noise is recognized as a physical form of pollution, negatively affecting Indoor Environmental Quality (IEQ) by causing disruptions and having adverse effects on the health and wellbeing of occupants. In this article, the fourth in our acoustics series, we’ll take a closer look at blocking environmental noise specifically, how to reduce noise pollution and improve the indoor acoustic environment. We’ll also look at the sources of noise pollution and its impact on the quality of an indoor environment.

The way construction materials manage exterior noise is rated differently from interior sound – we’ll explain how and the reasons why. The article will also address the various guidelines in place to protect people against noise pollution. From there we present practical information all building and design construction professionals need to know to construct buildings with materials such as stone wool that help reduce external noise, and by extension, support positive IEQ. Let’s get started.

What is noise pollution?

Noise pollution, also known as environmental noise or sound pollution, is any sound that negatively impacts the health or quality of human or animal life. In the built environment, urbanization is largely responsible for the increase in noise pollution by bringing infrastructure and buildings – residential, commercial and industrial – closer together.

Buildings can be affected by multiple competing external noise sources. External noise pollution examples range from railways to streetcars, airports, busy roads, and highways. Yes, infrastructure is crucial to urban life, but the consequence is that it can be very noisy. The resulting vibration and traffic noise – not to mention human noise pollution – can all have a serious and negative impact, especially in densely populated areas.

The importance of noise pollution control should not be overlooked. Repeated exposure to noise may reduce sleeping hours, productivity and efficiency at work, the recovery of hospital patients and the learning environment for students in schools.

Regardless of the source, the goal is to keep outside noises out. There are unique characteristics and challenges for exterior sound, and as a result, different strategies for how best to manage it. Managing exterior noise starts with understanding how it’s measured before we jump into the sources and solutions for the prevention of noise pollution. More on that below.

How is environmental noise measured?

Just like all sound, exterior noise is typically measured in decibels. Because exterior sounds, especially in urban areas, often exceed 80 dB, they fall into the range of what is considered excessive or pollution. Creating a comfortable living space for building occupants means architects and designers need to take into consideration different methods to control sound. Outdoor-Indoor Transmission Class (OITC) is one such method of understanding how the insulated assemblies reduce noise around the building.

The OITC rating was originally created to measure exterior walls and their elements (windows and doors). OITC also provides a number rating for roofs, facades and facade elements that are subjected to transportation and other exterior sources of noise. The higher the number, the better the noise isolation. When choosing building envelope designs, using the OITC rating as part of your criteria for material selection will provide more accurate results in particular when lower frequency noises are expected.

The differences between OITC and STC (Sound Transmission Class) can be confusing if you’re not working with them every day, so we’ve created a table to serve as a reference for you. At ROCKWOOL, our assemblies are tested for both STC and OITC ratings to ensure assembly performance under different frequency ranges.

What is the difference between OITC and STC?

What are the primary sources of noise pollution?

Noise pollution comes in many from many sources and there are numerous examples in our everyday life. Noise sources that are in close proximity to a home or building have a major impact on what type of building envelope should be used. As a physical barrier between the conditioned indoor and unconditioned outdoor environment, the building envelope should be expected to maintain consistent levels of noise protection. Outdoor to indoor noise reduction is essential, especially when you’re looking for how to isolate or negate the road noise and other sources of noise pollution in cities.

Five of the most common sources or examples of noise pollution are transportation, weather, construction, household activities, and heavy industry.

• Transportation: In urban areas, traffic congestion is only increasing and proximity to transportation infrastructure such as large or busy highways, airports, railways, and other public transportation hubs leaves people susceptible to higher levels of noise pollution. Despite the noise of aircraft and commercial jets decreasing over the past few decades, there are areas where noise getting into buildings is continuing to create problems.
• Weather: Have you ever been inside a building with a metal roofing system during a major storm or even a normal rainy day? When not properly designed for, the weather can be loud and distracting for those working indoors.
• Construction: Construction sites are naturally very loud and are one of the most frequent sources of noise pollution. Those living in colder regions of North America will be familiar with the two seasons – winter and construction. Despite the fact that bylaws in many communities now prohibit construction during certain times of the day, heavy machinery, power tools, and people (whether talking or listening to the radio) make construction site-related noise an ongoing challenge.
• Households: Common environmental noises from residential homes can include lawnmowers, leaf blowers, air conditioners, motorcycles, garage bands, and DIY construction or renovation projects.
• Heavy Industry: Sound pollution from industrial operations doesn’t just have the potential to impact the hearing of workers on site, but without the proper sound abatement mechanisms installed, there can be negative effects on the surrounding neighborhoods.

So what’s the solution to noise pollution?

There is no one-size-fits-all approach to preventing noise pollution, but a good place to start is to consider the use of the space and the potential noise sources early on during the planning phase of the project.

What are the health effects of noise pollution?

We’ve now heard about the sources of noise pollution, but what about the impact? Research shows that there are negative effects of being exposed to loud or constant noise in the workplace, in schools or hospitals and our day-to-day lives.

A study from C.Clark et al (2005) found that a 20 dB increase in noise reduces reading comprehension in children, while research by Stansfeld and Matheson (2003) proved that chronic exposure to continuous noise of at least 85 dB can cause higher blood pressure. More recently, J. Lim et al (2018) found that noise and noise sensitivity are negatively associated with the mental health of children and adolescents resulting in behavioral problems, particularly in low-income groups.

It makes sense that noise pollution effects are most commonly felt in urban areas. Here, exterior noise intrusion can pose a very real risk for certain health outcomes, given that commercial and industrial buildings and residential homes are often located more closely together. Even suburban neighborhoods where there are limits on the proximity to airports or other transportation hubs are known to experience a higher incidence of noise pollution.

When the World Health Organization (WHO) released a 2011 report titled ‘Burden of disease from environmental noise’, the study, which collected data over a 10-year period, proved that exposure to prolonged or excessive noise has been shown to cause a range of health problems. The authors found that at least one million healthy years of life are lost each year in Europe, where the study was conducted, as a result of noise pollution (not including noise from industrial workplaces).

In summary, what are the effects of noise pollution on human health? There are several, including stress, sleep deprivation, hypertension, hearing loss, the potential for mental health issues, among others. This research therefore also confirms that protection from unwanted noise can have a positive effect on our physiology, learning capacity and social behavior.

How can you control noise pollution? What are governments doing to regulate noise?

The use of continuous insulation (CI) in building enclosures is much more common today, in part because of more stringent building codes, advances in building science and an increased focus from building owners on creating comfortable environments.

Noise ordinances are typically established in areas in close proximity to airports; builders developing in areas with other significant noise sources (in addition to aircraft traffic) are also held to standards of minimum sound insulation in their construction projects. Specific requirements vary, but they almost all include direction on sound absorbency for exterior walls and roofing system designs to decrease the impact of noise pollution. It usually falls on governments, rather than industry or other interested bodies, to set noise limits as a means of reducing noise pollution; let’s take a closer look.

In the United States, the Environmental Protection Agency (EPA) has had noise protection legislation in place since the 1970s. That goes to show how long our understanding of noise pollution has been clear. The Noise Control Act of 1972 outlines policy to protect people from noise that jeopardizes their health and welfare. Other EPA noise pollution standards include the Clean Air Act, Title IV – Noise Pollution, essentially an update to the 1972 legislation, and the Model Community Noise Control Ordinance, which lays out the direction for communities to establish their own local guidelines. Additionally, the U.S. Code of Federal Regulations, the U.S. Department of Transportation, and the U.S. Department of Housing & Urban Development (HUD) provide guidelines around noise.

In Canada, modern noise control regulations begin with the Canadian Centre for Occupational Health and Safety, the Canada Transportation Act, Motor Vehicle Safety Regulations, and Health Canada (specifically related to wind turbine noise). Specific guidelines and enforcement are left to provincial and municipal governments.

The International Green Construction Code (IgCC)

The IgCC offers specific guidelines for builders around controlling noise in different environments. Presently, the code is developed for high-performance applications but is slated for inclusion in the 2021 International Building Code (IBC) update that will become mandatory. At that point, acoustics will become mainstream with statewide compliance throughout the U.S. Section 8.3.3.1 is titled Site Exterior Noise – focused on minimizing the effect of site exterior noise on building occupants. Under the code, wall and roof-ceiling assemblies must have an OITC rating of 40 or greater or an STC rating of 50 or greater, and fenestration that is part of the building must have an OITC or STC rating of 30 or greater for any of the following conditions:

• Buildings within 1000 ft. (300 m) of expressways.
• Buildings within 5 mi (8 km) of airports serving more than 10,000 commercial jets per year.
• Where yearly average day-night average sound levels at the property line exceed 65 dB.

ASHRAE and the International Energy Conservation Code (IECC)

Under ASHRAE 90.1 and within the International Energy Conservation Code since 2015, there is a requirement to use continuous insulation (CI). By using insulation across all structural members without thermal bridges, other than fasteners and service openings in exterior walls, your design can achieve improved energy efficiency. ASHRAE 90.1 has led to increased adoption of energy codes across the U.S. where architects are now specifying overall assembly performance to achieve prescriptive R-values.

In summary, while you should familiarize yourself with the code requirements for noise pollution for a new construction or renovation project, keep in mind that codes and regulations are considered the minimum standard. As the concerns around noise pollution have continued to increase, more stringent requirements have been developed to protect people who live in areas where it is a regular occurrence. Consider what you can do within your space to improve acoustic comfort such as reaching the LEED design requirements for exterior noise.

How can you block outside noise from entering a room or building?

There are three components to any plan for managing exterior sound: understanding the source-path-receiver model, selecting the right acoustic insulation for continuous exterior assemblies, and following general tips to soundproof from environmental noise pollution.

Part 1: Understanding the source-path-receiver model

When it comes to managing exterior sound, the source-path-receiver model continues to be useful. Looking at a commercial building, industrial facility, or even a residential home, the principle remains the same: start by looking at all the possible sources of noise and then look at all the possible entry points, or pathways, for the sound to travel. That list includes the roof, windows and doors, and wall assemblies.

Do you know which of these are the weakest sections of the building envelope when it comes to blocking external sound? You wouldn’t be alone if you assumed it was the exterior wall and roof systems. But you’d be wrong. Windows and doors are the most common culprit for allowing exterior sound to negatively affect the indoor environment.

That being said, building and design professionals are always encouraged to design exterior wall and roof insulation systems to help block as much of that environmental noise as possible. The overall mass of the wall and roof systems is what blocks most of the noise, but concrete alone isn’t usually sufficient, as it’s a poor medium for controlling other interior conditions, e.g. temperature. In addition, insulating exterior wall and roof systems means interior designers might even gain some freedom – needing fewer wall assemblies or other materials to block and absorb sound because the external noise is minimized by the building envelope.

Part 2: Selecting the right acoustic insulation for continuous exterior assemblies

Construction practices from architects and builders are important in reducing noise and sound transmission. Pay close attention to material selection for insulation. When it comes to acoustic insulation, noise sources near the building will have a major effect on what type of building envelope material should be used.

The strategy behind noise control with insulation? You can improve the indoor acoustics and reduce stressors by limiting structure and airborne transmission from external sources by integrating sound reduction measures into the basic planning and layout of your home or building.

Consider the following checklist when evaluating the insulation to use in your CI applications, which as outlined above, is now a required practice under most building code legislation.

• Raw materials used in manufacturing the insulation
• Manufacturing processes
• Operational performance
• Combustibility of the insulation
• Moisture mitigation properties
• Overall durability
• Impact on acoustic performance (OITC / STC)

While building codes and material costs should be a component of your selection process, the desired performance factors for your commercial office, healthcare facility, educational institution or other structure, are most important when evaluating and specifying products to deliver CI.

Stone wool insulation is well suited to deliver sound reduction benefits and control unwanted noise in occupied spaces. When properly installed in today’s building enclosures on the outside face of the building substrate behind the building facade, stone wool, as part of your CI system, supports thermal performance and provides additional acoustic comfort.

When the building enclosure is wrapped in stone wool insulation, it provides exterior wall OITC rating results that improve productivity, health, and wellbeing for those within the space. Block environmental noise pollution from neighbors, traffic, airplanes, construction sites and more by planning a good acoustics approach from the beginning with your choice of acoustic insulation.

Common assembly combinations and the resulting OITC:

Part 3: Tips for soundproofing from environmental noise pollution

To soundproof your building from environmental noise pollution, consider the acoustical performance of every assembly on the building envelope. Noise travels through the weakest sections of the building envelope, meaning the effectiveness of a high-performing wall or roof system may be reduced when the rest of the building is not equally designed.

In many cases, unwanted noise can enter the building under a door, through a window, your roof, or a connected exterior wall. This type of noise is called flanking noise. The assembly and its connecting features should be tested during the planning stage of a project to minimize flanking through the building envelope, especially the parts of the enclosure that are known deficits in a wall or roofing design (e.g. windows and doors).

Review and consider all of the following applications during the planning process of your next project:

• Roofing: Stone or mineral wool insulation has superior sound abatement properties, which is essential when designing today’s roof system. High-performing systems using stone wool insulation can add mass layers to assist with improving the sound attenuation properties of the assembly. Research has shown dense acoustic roof insulation, including stone wool flute fillers, are an effective solution to reducing sound transmission through a roof.
• Connecting assemblies: Areas of deficiency for façade sound transmission paths can be things such as roof soffits, vents, fans, air sealing details and probably many others depending on the type of façade system being constructed.
• Exterior wall systems: How can you reduce exterior noise coming in through walls? For starters, the addition of better acoustic performance in your exterior wall assemblies comes down to the type of construction and the building materials being used. All insulation for exterior walls should be designed to meet or exceed energy code. Soundproof your exterior walls using the right materials that offer improved acoustic performance (like stone wool) while still meeting the other demands of your assembly to create cost-effective solutions and more livable spaces. For example, foam plastic insulation with multiple layers of gypsum could be optimized with stone wool insulation and a single layer of gypsum.
• Windows and doors: Windows are one of the largest deficits in building wall design for acoustical control and heat loss. Pay careful attention when designing the windows and their connections to the wall elements for a high-performance wall system. Consider the type of window (we recommend double- or triple -pane for best soundproofing), the pane thickness and how it will be installed.

The higher the likelihood of exterior noise (i.e. traffic noise or aircraft) the more assemblies including the roof-ceiling and exterior walls should be focused on sound isolation. All exterior penetrations and joints between components should be sealed as required for thermal performance which will also improve the building acoustics.

The common thread throughout these tips for soundproofing from environmental noise pollution is using stone wool which provides a high-density acoustic insulation solution. This makes the insulation resistant to airflow and excellent at noise reduction and sound absorption. This means that even the loudest infrastructure will sound quieter for occupants living, working or learning inside the structure. See below for an overview of three assemblies focused on the exterior walls and roof systems of the building and demonstrating which combination of construction and materials provide the highest levels of STC, OITC, and R-Value.

1. An acoustic baseline for wall assemblies

2. High-performance enclosures: stone wool insulation wall systems

3. High-performance enclosures: stone wool hybrid roof systems

Bringing it together – applying the science and technology of acoustics to building design

With indoor environmental quality (IEQ) top of mind, the goal for the acoustic plan of a building should be to design comfortable and productive spaces that reduce the impact of external noise pollution. Architects and designers can gain some design freedom by looking at the building, and the acoustics plan, holistically.

Much of a building’s sound blocking can be achieved through the building envelope – essentially stopping noise from coming in from the exterior to minimize the amount you need to do on the interior. Architects and designers are instead encouraged to incorporate sound control measures to block out external noise especially when using features like open plenum design. For example: develop quiet spaces away from outside noise sources to create distance between the receiver and the noise source.

Insulation is one of the basic and most practical ways to reduce noise pollution in homes and non-residential buildings. Common noise barriers and exterior flanking paths should be considered when marrying acoustics strategies with design. Another determinant of the external noise environment is the building location itself. Proper site planning and the use of berms and barriers can support noise level reduction (NLR), particularly from ground-level sources.

Summary

Noise pollution is a growing concern, and while exterior environmental noise is a reality, there is a solution. Building design and construction professionals need to consider environmental noise pollution along with all other acoustical needs early in the project planning process – whether it’s new construction or a renovation/retrofit.

Increasingly, governments are recognizing the negative impact that external noise can have, and are creating regulations to limit its impact. Those regulations are a good starting point, but there is much more that can be done. By considering the various sources of noise, as well as the potential paths for sound to travel into a building, and then selecting the right design, construction assemblies and materials to mitigate that noise, spaces with high acoustic comfort can become the norm.

Ultimately, the unique acoustical needs of each space should guide the plan, but as these recommended considerations are slowly becoming standard practice in building design, external noise control will help improve the experience for building occupants.