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

An example of base isolation below raft foundation to minimize noise and vibration levels.
An example of base isolation below raft foundation to minimize noise and vibration levels.

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.


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.

Figure 1: Duct interference with the wall. Photos courtesy Aercoustics
Figure 1: Duct interference with the wall.
Photos courtesy Aercoustics

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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