Party walls, also called demising walls, are essential to any multi-family building. Party walls provide separation between dwellings. They must provide fire and noise resistance specified in the Ontario Building Code (OBC).
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The Ontario Building Code (OBC) specifies the minimum noise resistance between dwelling units—often referred to as party wall soundproofing—as follows:
A Sound Transmission Class (STC) rating of at least 50, or
An Apparent Sound Transmission Class (ASTC) rating of at least 47 when tested in the completed building.
However, this requirement applies only to buildings constructed in 2012 or later. Buildings built before 2012 are not subject to these sound insulation standards, and as a result, their walls and floor assemblies may provide lower levels of acoustic separation than what is currently expected under modern codes.
How much party wall soundproofing does one need?
The OBC specifies a minimum level of soundproofing. About 45% of people are unsatisfied with this level of soundproofing.
Pathways for noise
Noise transmits through a building structure in two distinct ways: airborne and structure borne.
Airborne
Airborne noise penetrates the party wall directly. Sound waves impact one side of the wall and retransmit on the other side. The ability of the wall to resist the noise transfer is rated as Sound Transmission Class (STC).
Impact
The impact of objects on the floor of a dwelling (footsteps, dropped objects, shuffling furniture) delivers noise energy directly to the building structure. It transmits through the building more readily and further than airborne noise. This noise is audible below the apartment, causing the noise, but also in adjacent spaces sideways and above.
The ability of the floor/ceiling to resist the impact noise transfer is rated as Impact Insulation Class (IIC). There is no mandated requirement for an IIC value. The OBC recommends a minimum IIC 55.
Investigation of noise complaints
Many people contact me asking whether the noise in their apartment is excessive. This is a difficult question to answer, because there is no formal definition of what constitutes “excessive noise.” The term is inherently subjective — what one person finds intolerable may be entirely acceptable to another.
As an acoustical engineer, I can perform tests to determine the soundproofing performance of a party wall. Such a test provides the Sound Transmission Class (STC) rating, showing whether it meets or falls below the Ontario Building Code (OBC) requirement. However, in most cases, testing is unnecessary, since the STC value can be estimated quite accurately from the construction details of the wall or floor assembly. Testing is only warranted when the assembly details are unknown, unusual, or when a hidden acoustic fault (such as a gap or flanking path) is suspected.
A common complaint involves children running or other activity in the apartment above — this is a form of impact noise. Such cases are more complex, because the OBC does not mandate, but only recommends, a minimum Impact Insulation Class (IIC) of 55. Testing the IIC is often not useful, as there is no legal standard to compare results against, and even when the IIC meets or exceeds 55, many residents may still find the impact noise disturbing.
Fixing the problem
If you are experiencing airborne noise or impact noise problems, there are methods available to mitigate these issues. Effective noise reduction typically involves enhancing or reconstructing the affected wall or ceiling assembly to improve its sound isolation performance.
It is essential that this work be carried out by a contractor experienced in soundproofing, as improper construction can render even high-quality materials ineffective. Before hiring a contractor, you should consult an acoustical engineer or consultant to ensure that the proposed solution is technically sound and appropriate for your specific situation.
