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# STC Rating Explained: Toronto Construction Reference 2026
Every Toronto soundproofing conversation eventually arrives at one number: STC. Sound Transmission Class is the single most important metric in residential acoustics, the threshold the Ontario Building Code uses to define "good enough" between dwelling units, and the number you will see on every product spec sheet, manufacturer assembly listing, and renovation quote that is worth its paper. Understanding what STC actually measures — and equally important, what it does not measure — is the difference between a renovation that solves the problem and one that produces a beautifully finished wall that still leaks sound.
This post is the Toronto plain-English reference for STC ratings: what each level sounds like in practice, how lab-tested STC differs from field-built STC, the OBC 9.11 mandate, and the typical assemblies that hit each target. For full pillar context see [Acoustic Soundproofing Renovation Toronto](/blog/acoustic-soundproofing-renovation-toronto-2026-complete-guide).
Honest Positioning
RenoHouse builds STC-targeted assemblies as standard renovation work. We use manufacturer-published assembly listings (NRC-CNRC, IRC-NRC, ASTC, manufacturer test reports) for design. We do not perform field STC testing in-house; that is an acoustic consultant's role on the rare project where it is required. For most Toronto renovations a published-listing match is sufficient for plan approval.
What STC Measures
Sound Transmission Class is a single-number rating derived from a partition's transmission loss measured at 16 frequencies between 125 Hz and 4000 Hz, weighted to the way human hearing responds to those frequencies. It is defined by ASTM E413 and tested in a lab per ASTM E90.
Translation: it tells you how well a wall, floor-ceiling, door, or window blocks typical speech, music, and TV content. Higher is better.
What it does not capture well:
- Low-frequency content below 125 Hz. Bass from subwoofers, traffic rumble, HVAC vibration, and footsteps all have significant energy below 125 Hz that STC effectively ignores. A wall rated STC 50 may pass shocking amounts of sub-100 Hz bass if the assembly is mass-only and not damped.
- Impact noise. Footsteps, dropped objects, chair drags. These are rated by IIC (Impact Isolation Class), a separate metric for floor-ceiling assemblies.
- Flanking noise. STC tests measure transmission through the partition only. Real walls leak sound around the edges — through shared HVAC ducts, electrical boxes, plumbing chases, perimeter joints. Field STC (FSTC, ASTC) is typically 5-10 points lower than lab STC for the same construction because flanking is included.
The Toronto STC Reference Scale
What each level actually sounds like:
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- STC 30: Standard 2x4 wall, drywall both sides, no insulation. Most older Toronto interior partitions. Loud speech is intelligible; you know what the conversation is about.
- STC 35: 2x4 wall with batt insulation, drywall both sides. Most newer Toronto interior partitions. Normal speech is muffled but loud speech is still intelligible.
- STC 40: Tuned 2x4 wall — batt insulation, gasketed boxes, sealed perimeter. Loud speech is muffled; normal speech is mostly inaudible. Acceptable for most bedroom-to-living-room walls within a single dwelling unit.
- STC 45: Resilient channel + double 5/8 drywall, or RC + Green Glue. Loud speech faintly audible; TV at normal volume largely blocked. Comfortable.
- STC 50: OBC 9.11 mandate between dwelling units. AcoustiClips + Green Glue + double drywall. Loud speech inaudible. TV inaudible at normal levels. The threshold at which neighbours stop hearing each other in normal living conditions.
- STC 55: Multiplex demising wall with double-leaf treatment. The level most premium Toronto multiplex projects target as the design value to ensure STC 50 in the field.
- STC 60: Premium home theatre. Loud movie audio largely contained. Approaching recording-studio territory.
- STC 65-70: Room-within-room construction. Drum kit at full volume in one room, conversation possible in the next.
Lab STC vs Field STC: The 5-10 Point Discount
This is the single most important practical fact about STC and the reason multiplex contractors design to STC 55 on the drawings to deliver STC 50 in the field.
A lab-tested STC assembly is built in a controlled chamber with no flanking paths, ideal mass-loaded edges, and perfect workmanship. A field-built STC assembly is built into a real building with shared HVAC, electrical, plumbing, perimeter joints to floor and ceiling, and normal trade tolerances.
The typical field discount is:
- 2-3 points on a meticulously executed assembly with sealed perimeters, gasketed boxes, no flanking paths.
- 5-7 points on a typical good-workmanship assembly.
- 10+ points on a poorly executed assembly with non-gasketed boxes, perimeter gaps, or short-circuited resilient channel.
For an OBC 9.11 multiplex demising wall, the practical implication: design to a published lab STC of 55 or higher to ensure STC 50 field. Inspectors generally accept a published listing above 50 as evidence of code compliance, but if a field test is requested (rare) you do not want to be at the lab-STC-50 floor.
The OBC 9.11 Mandate
The Ontario Building Code section 9.11 requires:
- STC 50 minimum between any two dwelling units (walls, floors, ceilings shared between units).
- STC 55 minimum when the wall separates a dwelling unit from a public corridor with normal traffic and ambient sound.
- STC 60 minimum in some specialized cases (e.g., dwelling unit to a mechanical room or commercial space).
There is no STC requirement within a single dwelling unit. The bedroom-to-living-room wall in your detached home is not regulated. STC 50+ is only required across dwelling-unit boundaries.
For multiplex licensing in Toronto under the City's permissive multiplex bylaw, plan-examiners require either a published assembly listing on the drawings or a field test. Most projects use the published-listing path. See [Multiplex Soundproofing STC 50 Toronto](/blog/multiplex-soundproofing-stc-50-toronto) for the full multiplex-specific workflow.
Assembly Reference: What Hits Each Target
These are typical published-listing assemblies as of 2026. Always verify the current listing for the specific manufacturer at the time of design.
STC 35 — Standard 2x4 wall:- 2x4 wood studs at 16" o.c.
- Single 1/2" drywall both sides
- R-13 fibreglass batt insulation
- No special detailing
- 2x4 wood studs at 16" o.c.
- Single 5/8" Type-X drywall both sides
- R-15 stone wool batt (Roxul Safe'n'Sound)
- Acoustic sealant at perimeter
- Gasketed electrical boxes
- 2x4 wood studs at 16" o.c.
- RC-1 resilient channel one side
- Single 5/8" Type-X drywall both sides
- R-15 stone wool batt
- Acoustic sealant + gasketed boxes
- 2x4 wood studs at 16" o.c.
- Two layers 5/8" Type-X drywall both sides with Green Glue between
- R-15 stone wool batt
- Acoustic sealant + gasketed boxes
- 2x4 or 2x6 studs
- AcoustiClips + hat channel one side
- Two layers 5/8" Type-X drywall on the decoupled side with Green Glue between
- Single or double layer 5/8" on the other side
- R-15 or R-23 stone wool batt
- Acoustic sealant + gasketed boxes
- Two independent 2x4 stud walls with 1" gap, separate plates
- Two layers 5/8" drywall each side with Green Glue
- Stone wool in both cavities
What This Means for Your Project
If you are renovating within a single dwelling unit, target STC 40-45 for comfort upgrades and STC 50 for premium scopes. There is no code requirement; pick the budget tier that matches the noise problem.
If you are renovating a multiplex, duplex conversion, or anything that crosses a dwelling-unit boundary, target STC 55 on paper to ensure STC 50 in the field. Use a published assembly listing that matches your construction.
If you are building a home theatre or recording space, target STC 60-70, plan for room-within-room construction, and budget accordingly.
For the cost-per-square-foot of each target see [Soundproofing Cost Toronto Comparison](/blog/soundproofing-cost-toronto-comparison). For the material decision behind these assemblies see [Green Glue vs Resilient Channel Toronto](/blog/green-glue-vs-resilient-channel-toronto). Or book a scoped estimate through the [home renovation service page](/services/home-renovation/acoustic-soundproofing-renovation).
