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.
Image courtesy the Federal Highway Administration
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.
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.
