What STC rating does the Ontario Building Code require for walls between dwelling units?

The Ontario Building Code requires a minimum STC 50 rating for party walls between dwelling units — but most acoustic professionals consider this the floor, not the target.

Why STC 50 Is Just the Starting Point

STC 50 means that loud speech is faint or inaudible through the wall, but it does not mean you will not hear your neighbours. At STC 50, loud music, television at normal volume, and impact sounds like footsteps can still be clearly audible. This is why the code minimum often disappoints homeowners in Ottawa condos and townhouses who assumed "built to code" meant "built for comfortable living." It does not.

The STC scale works roughly like this: each 10-point increase represents a perceived halving of loudness to the human ear. So the difference between STC 50 and STC 60 is not minor — it is the difference between hearing your neighbour's TV as a faint murmur versus not hearing it at all under normal conditions.

For most Ottawa homeowners and condo owners, STC 55 is the practical minimum for comfortable living, and STC 60 or higher is recommended for home theatres, music rooms, or any space where serious noise control matters. If you are in a Centretown high-rise or a Barrhaven townhouse and you are planning a party wall upgrade, targeting STC 55 to 60 gives you a meaningful quality-of-life improvement over the code minimum.

The OBC also sets a minimum IIC 50 for floor-ceiling assemblies between units — the Impact Insulation Class rating that governs footstep and impact noise transmission. Again, IIC 50 is a legal minimum, not a comfort standard. In Ottawa's older condo buildings, many floor assemblies fall well below even this threshold, which is why impact noise complaints are so common in converted heritage buildings in neighbourhoods like the Glebe or Sandy Hill.

One important practical note: STC ratings are lab-tested values. Real-world field performance — called FIIC or FSTC — is typically 3 to 5 points lower than the lab rating due to flanking paths, construction imperfections, and gaps in the assembly. This means a wall assembly rated at STC 52 in a lab may only perform at STC 47 to 49 in your actual home. Specifying assemblies that exceed the minimum by a comfortable margin is always wise.

From a permit standpoint, any renovation that modifies a party wall in a multi-unit building in Ottawa requires a building permit from the City of Ottawa — apply through ottawa.ca or by calling 3-1-1. The permit process ensures the assembly meets or exceeds OBC minimums, and the inspector will want to see that fire ratings are maintained alongside the acoustic performance. Never remove or modify fire-rated drywall layers in a party wall without understanding the fire separation requirements — acoustic upgrades and fire compliance must work together.

For a project involving party wall upgrades, it is well worth consulting with an experienced soundproofing contractor who can assess your existing assembly, identify flanking paths, and recommend an approach that genuinely exceeds the code minimum rather than just meeting it. You can find soundproofing professionals serving the Ottawa area through the Ottawa Contractor Directory at justynrookcontracting.com/directory.