Acoustical considerations when building on less-than-ideal urban plots

by sadia_badhon | March 27, 2020 10:56 am

By Nicholas Sylvestre-Williams, P.Eng.

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For years, many in the construction industry have complained about the shortage of buildable land in major cities such as Toronto. From an urban planner’s perspective, good land means it is well set back from industrial areas and noisy transportation sources. For example, parking lots situated in the city’s core were easily converted to condos. They were ideal sites because of their proximity to other residential buildings or quieter commercial or office facilities. However, these good plots of land are becoming scarce. Therefore, developers need to expand their search.

In many cases, what remains of urban land is less than ideal for construction and has typically been difficult to obtain permits for because they are close to railway lines, highways, airports, or encroaching on existing, established industry. This type of land presents new construction challenges, including keeping the noise and vibration at bay.

For years, there was a prevalent belief distance is the only tool to deal with noise issues. A lack of land affordability and availability in the city core was one of the many causes of urban sprawl, as suburbs rapidly grew to accommodate the increasingly large population. However, many are opting to stay in urban areas for a shorter commute to work or to minimize their carbon footprint.

Regardless of the reason, demand continues to exceed supply. A 2019 report[2] by the Royal Bank of Canada (RBC) found Toronto would need to double the amount of condo and apartment construction to meet future demand. So, it is no surprise an increasing number of developers are looking to build on less-than-ideal plots of land.

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The questions are how to build in the margins, and how to ensure acoustic comfort for those who will be living or working in buildings close to sources of noise and vibration? Also, how to make it affordable so a mid-rise building can be viable.

Understanding regulations

Before delving into acoustical considerations in construction, it is very important to understand the regulations. The province of Ontario is heavily invested in protecting its infrastructure, to the point where the Provincial Policy Statement[4] (PPS) says in Section 1.6.9.1, “Planning for land uses in the vicinity of airports, rail facilities, and marine facilities shall be undertaken so that a) their long-term operation and economic role is protected; and b) airports, rail facilities, and marine facilities, and sensitive land uses are appropriately designed, buffered, and/or separated from each other […].” This means when a development is proposed, the existing airport or rail facility’s use must be considered first and foremost, and a developer cannot simply build closer without ample demonstration of compatibility and suitability.

Due to the PPS, most Ontario municipalities have a robust acoustic criterion to meet, both for outdoor noise levels at people’s windows and at outdoor locations. There are also indoor sound levels to be met from road, rail, and aircraft noise. As such, when considering constructing on lands near noisy sources (i.e. industries, road, rail, or aircraft), the design freedom will be impacted. This means one may need to reorient the building’s design to ensure noise levels are met or introduce premium architectural elements. These sites are not suited for a cookie-cutter approach. Rather, a unique view needs to be taken to address the site’s specific needs.

The technical details on the limits are quite involved, but as an example, noise from an airport such as the Toronto Pearson International Airport, is presented in the form of a noise exposure forecast (NEF). The forecast is shown on a map and gives the developer an idea of the expected noise level if they were to build in an area. Transport Canada advises an NEF level greater than 30 is likely to produce some amount of annoyance and that above 35, complaints will surely be numerous. As such, the PPS prohibits new residential development near airports with an NEF above 30. Despite this provincial limitation, there are developments of sensitive land uses that have occurred in areas exceeding NEF 30, with appropriate acoustic insulation features[5] incorporated in the building.

Another example of the challenge of constructing near noisy infrastructure is near busy highways. Road noise has a different set of limits that need to be met, and they vary based on time of day and location. For example, the daytime limits are met outdoor and the nighttime limits indoors. Note, there are outdoor limits for nighttime as well but they are not the restricting factor because if the outdoor daytime limits are met, the nighttime limits will be satisfied as well.

Also, nighttime indoor limits themselves vary depending on the space (i.e. 40 dBA bedrooms and 45 dBA for living rooms) and these all need to be assessed and demonstrated to comply with the municipality’s requirements.

It is important to keep in mind, the guidelines set out by the municipality are not strict. The limits do not mean they will not be a problem, only that they will minimize complaints. Bodies like the Canadian National Railway (CNR) or the Toronto Transit Commission (TTC) do not want to rely on minimum standards, they want to ensure the developer’s do everything they can so they will sometimes ask for more than just what the minimum standards are. When the neighbours are the CNR or the TTC, one may need their buy-in when it comes to concessions. When considering constructing near one of these authorities’ lands, in the zoning, planning, and approval process, these authorities have the right to object if they feel the development will cause problems once residents move into the buildings. The authorities also have significant resources and experts who will dive deeply into the technical studies and require justification until they are satisfied the development does not pose any risk to them.

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While it is not ideal to build on the leftover plots of land near potential sources of noise or vibration, there are measures that can be taken during the design process to proactively address any issues and to ensure acoustic comfort.

Incorporate a blank wall

Exterior noise enters a building through a number of pathways. The primary pathway is windows. In Toronto’s waterfront community, a recent condo development went up beside the Redpath Sugar Refinery. One entire wall facing the factory has no windows at all or the windows lead to a corridor creating a buffer to the noise. It was an unusual design at the time, but it is a creative solution on an unconventional site.

Upgrade exterior windows, doors, and walls

Upgrading windows can significantly minimize sound transfer as they are a primary entry point for noise. The heavier the glass panes and greater the airspace between them, the better the noise isolation. Standard designs  are double-glazed windows (i.e. two glass layers, typically 6 mm [236 mils] thick, separated by an airspace, usually 13 mm [511 mils] thick). While these are good for both thermal and acoustic isolation, larger airspaces or triple-glazed windows are an even further upgrade. This means a layer of glass, typically 6 or 8 mm (315 mils) thick, an airspace, more than 13 mm thick, a layer of glass, a second airspace, and finally, a third layer of glass. A good airtight seal will also improve noise isolation. Having laminated glass as one of the layers also improves the acoustic performance. Laminated glass means instead of a single layer of 6-mm glass, there will be two layers of 3 mm (118 mils) glass with thin glue between the panes.

For exterior walls, the mass principle applies here: the thicker the wall, the more noise resistant it will be. Adding mass makes the building elements heavier and improves soundproofing. Using masonry brick or concrete exterior elements, as opposed to wood or glazing, will significantly reduce noise trickling into the interior space.

STC VERSUS OITC

The downside of sound transmission class (STC) is it was originally developed to address speech. Without getting complicated, STC tests only consider sound in the frequency range of 125 to 4000 Hz. This encompasses the range of frequencies people speak at, and does a reasonable job covering the frequencies from road traffic, but it does not account for the noise levels generated from rail and aircraft (which can often be much lower in frequency). Relying on only the STC rating to address these types of sources, which generate significant low-frequency noise, may end up missing the design intent. Other acoustic metrics do a better job in accounting for low-frequency noise such as outdoor-indoor transmission class (OITC). It is similar to STC except it starts at 80 Hz, instead of 125. The OITC rating system was designed to measure the transmission of street sounds such as car horns, sirens, construction, airplanes, trains, etc., through exterior walls, windows, and façades. It is uncommon for walls to have an OITC element but often there is no OITC ratings on windows, and this can give a good idea of the low-frequency performance. Simply, the difference between STC and OITC indicates the low-frequency performance. Generally, the greater the difference between STC and OITC, the worse the low-frequency performance.

For example, if the building is near a rail line, the sound from a large diesel train will generate a lot of low-frequency noise, which is difficult to mitigate, so the design should incorporate better, thicker (heavier) windows, doors, and walls. Low-frequency noise is not well-accounted for in municipal and provincial standards. Therefore, while there is a target to achieve for sound, it is a minimum, so consider going beyond that requirement to make the space more livable. It is also important to keep in mind, the lab tests always perform better so it is worth going even beyond that target so the actual field performance meets the requirement expectations.

The overall amount of sound a wall will reduce is called the sound transmission class (STC) and is a single number value to represent how well a wall reduces sound. Generally, the higher the number, the less sound is transmitted.

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If a project is under a flight path, the architectural features will need to be upgraded. A standard detached home has a roof of plywood, shingles and siding, or stucco or brick veneer, and insulation. This needs to be upgraded with sheet metal roofing, a second layer of drywall, upgraded acoustic insulation, concrete, or masonry, and in some cases, heavier drywall or cement board (although brick veneer is not too different from masonry [brick veneer is about 76 mm (3 in.) of brick, while masonry is a full brick] they are both good, and significantly better than normal stucco or siding material). Generally, the denser the wall material, the more noise is reduced. Improvements to an exterior wall or roof element can result in as much as a 10-dB reduction in sound. Adding small things like resilient channels or clips on the interior can also be effective. While the noise will not be completely inaudible, it will not be a nuisance.

Design an enclosed balcony

If one is looking to significantly reduce noise from an industrial operation, then the windows must remain closed. An enclosed balcony, much like a solarium with non-operable windows will minimize exposure to noise. It is an effective way to control sound because it removes the operable window as a point of reception in the ingress pathway. However, this may not appeal to everyone due to the fishbowl effect and the inability to open windows even though many open balconies are commonly unused.

Take advantage of screening or shielding opportunities

If a new development is incorporating commercial or office buildings, it is important to locate those buildings where the noise is loudest to help shield homeowners from the excessive sound. In many multi-use developments with towers, there are commercial or office buildings around the perimeter with residential blocks in the centre, pushing the homes further away from the noise source. A long building, or a row of structures parallel to a highway can shield other more distant facilities or open areas from noise. It is also important to note, gaps or small open spaces in between buildings do make a difference because they allow noise to come through and, therefore, need to be accounted for in the design.

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Isolate the building

When constructing next to a railway or subway, noise is not the only concern. Vibration is also an issue and can be both ground and structure-borne. An example of structure-borne vibration is sound travelling through a material (e.g. hearing the neighbours in a high-rise building drilling in their wall, or hearing the noise from a train line because the rail and ground are reemitting the noise, or people hearing the TTC in their basements). The vibration travels in the ground, and if strong when it reaches the building, it can shake things to the point of discomfort to the owners. Even if the vibration is not sufficient enough to cause shaking, it could have the strength to move the walls or floors so much so they become giant loudspeakers by re-radiating the noise. This phenomenon is known as vibration-induced noise and can occur at levels well below where vibration may otherwise be felt.

The best option to control vibration is to completely isolate the building by placing it on soft rubber padding. Similar to the giant springs in a car’s suspension, the soft material prevents the transmission of the force to the building when the vibration hits, and the occupants do not experience the noise or motion. Isolating a building entirely can be costly depending on the structure’s size, but based on proximity to the rail line, it is sometimes the only solution to ensure compatibility (meeting the city and province’s noise and vibration limits) and owner comfort.

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For someone looking to buy a property in a city in one of these less-than-ideal locations, one might expect it to cost less. The reality is the price of the land might be slightly less but the cost of construction and design to ensure the noise is not a nuisance may be significantly higher than typical build projects.

The implication to the design and the costs are considerable but the benefit is lands that might have been deemed unusable in the past can now support housing and higher density buildings. Instead of moving further out to build, developers and municipalities can increase density and build closer to city centres.

If developers want to build on existing plots of land, it is critical they put aside pre-existing notions and cookie-cutter designs and create a unique design that works for a particular site. They are constructing communities with multiple phases and will be interacting with a particular community for many years so whatever is done, needs to be done right the first time.

Unfortunately, no tests can be performed at this time by a potential buyer or consultant to evaluate the building’s performance before purchasing the property. The current standards mostly focus on design and they are either expensive to test in the field or they do not give definitive pass/fail answers.

Construction considerations

Once the design is complete and construction starts, it is important for the contractor and the trades to understand that everyone needs to work together to ensure the acoustical intent of the design is properly maintained. A seemingly insignificant imperfection in the sound isolation assembly can reduce its effectiveness. Co-ordination is critical to a successful outcome. This includes ensuring the mechanical system/supports take into consideration the location of walls (Figure 1). Electrical installations can short-circuit double stud walls if laid out without thought (Figure 2).

Periodic site reviews by the acoustic consultant can help educate the trades on the importance of the acoustical details and identify construction issues. A competent acoustic consultant will also foresee potential problems before the actual construction is completed. The ultimate goal is to build the acoustic elements correctly once, and not have to get the contractor to fix issues after the fact.

Depending on the contract requirements, post construction measurements may be required to verify the acoustical isolation and background noise requirements have indeed be achieved. Mockups can be an effective tool to help the contractor understand the detailing requirements. If mockups are going to be tested for acoustical isolation, specific room construction requirements are needed to be in line with the measurements standards, so it is advisable to confirm with the project’s acoustical consultant on those requirements before co-ordinating the mockup construction.

For projects with significant noise challenges, the author also recommends including an acoustic/vibration engineer in the design team.

Conclusion

Developments in densely populated cities are no longer a simple task. Due to the economics and the reality of the low supply of land and high demand for places to live, developers must now consider lands they would not have otherwise built on. As discussed, those lands pose challenges, otherwise, they would have been built already. These challenges are not insurmountable, but they are not trivial either. A thorough and careful look at the acoustic challenges is a worthwhile exercise prior to proceeding further on developments, especially during the planning and construction of the project.

[10]Nicholas Sylvestre-Williams, M.Eng., P.Eng., is a partner at Aercoustics Engineering Ltd., a privately held engineering consulting company. He has more than 13 years of experience in the field of acoustics, noise, and vibration. Sylvestre-Williams works on architectural and environmental projects, and has completed several studies on noise and vibration impacts for many proposed and existing buildings. Sylvestre-Williams can be reached at nicholass@aercoustics.com[11].

Source URL: https://www.constructioncanada.net/acoustical-considerations-when-building-on-less-than-ideal-urban-plots/

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