The Trouble With Party Wall Soundproofing

Mechanical noise and noise complaints

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). The noise resistance (level of party wall soundproofing) is specified in the OBC as minimum Sound Transmission Class (STC) 50 or, if tested in the completed building, as minimum Apparent Sound Transmission Class (ASTC) 47.  However, this requirement does not apply in Ontario to buildings built before 2012.


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.  Read more about this in our other blog.

Pathways for noise

Noise transmits through a building structure in two distinct ways: airborne and structure borne.


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).


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. Read more about impact noise here.

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 call me asking to determine if the noise in their apartment is excessive. This is a problematic request.  There is no formalized definition of “excessive noise.”  This term is subjective.  What is excessive to one person may be acceptable to another.

As an acoustic engineer, I can only test the soundproofing of the party wall.  The test will show if the STC value is above or below the building code requirement.  In most cases, the test is unnecessary because I can estimate the STC value of the partition simply by knowing the details of the partition assembly. I recommend testing only if the assembly cannot be determined, is unusual, or there is a suspected hidden acoustical fault in the assembly.

 A common complaint is children running in the apartment above the complainant. This is impact noise. In the case of impact noise, the situation is more complicated.  Ontario Building Code does not mandate but only recommends a minimum IIC of 55.  In most cases, it is pointless to test the IIC because a value is not mandated.  Some people complain even if the IIC is 55 or above

Fixing the problem

If you experience airborne noise or impact noise problems, there are ways of mitigating the noise.  This requires enhancing or rebuilding the wall or ceiling in question.  This must be done correctly by a contractor experienced in soundproofing.  I suggest you consult an acoustical engineer before hiring a contractor.

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About the Author Ivan Koval

The author is the publisher of the Soundproofing.Expert website. He is a soundproofing and building acoustics consultant working in Toronto and GTA, Ontario, Canada. Telephone (416) 471-2130

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