Multiplex Soundproofing STC 50 Toronto: OBC 9.11 Compliance 2026

# Multiplex Soundproofing STC 50 Toronto: OBC 9.11 Compliance 2026

Toronto's multiplex bylaw — adopted in 2023 and clarified through 2024-2025 — has produced a wave of duplex-to-triplex and detached-to-fourplex conversions across the city in 2026. Most of these projects share a common technical bottleneck: the existing demising walls and floor-ceiling assemblies in 1920s-1980s Toronto wood-framed houses fall well short of the OBC 9.11 STC 50 minimum between dwelling units, and bringing them up to code is a substantial portion of the renovation budget. This post is the practical multiplex soundproofing guide for 2026 — what plan-examiners accept, what assemblies actually work in the field, and how the acoustic scope coordinates with the fire-separation requirements.

For pillar context see [Acoustic Soundproofing Renovation Toronto](/blog/acoustic-soundproofing-renovation-toronto-2026-complete-guide). For the fire-separation companion scope see [Multiplex Fire Separation OBC Toronto](/blog/multiplex-fire-separation-obc-toronto).

Honest Positioning

This is the one part of the soundproofing niche where the regulatory stakes are highest, and we want to be exact about division of labour.

RenoHouse handles the renovation execution end to end: drywall, insulation, framing, electrical box rework, finishing, sub-trade coordination across electrical, plumbing, HVAC, and the fire-separation work. This is standard renovation, no specialist trade licence needed. Plan-examiners require either (a) a published assembly listing on the drawings that matches the as-built construction, or (b) a field STC test by an acoustic consultant. Most multiplex projects use option (a) with manufacturer NRC-CNRC, IRC-NRC, or ASTC published listings. Option (b) is required only when the as-built deviates from a standard listing or when an inspector specifically requests verification — that is the point at which RenoHouse coordinates with a Toronto-area acoustic consultant.

In short: the work is mainstream renovation; the design references published lab data; the only specialist engagement is for the rare field test. We do not self-certify field STC.

OBC 9.11: What the Code Actually Says

The Ontario Building Code section 9.11 requires:

• STC 50 between any two dwelling units (party walls, shared floor-ceilings, shared ceilings).
• STC 55 when a dwelling unit shares a wall with a public corridor that experiences normal pedestrian traffic.
• STC 60 in rare cases (mechanical rooms, parking garages, commercial neighbours).

There is no impact-isolation (IIC) mandate in OBC 9.11 — only airborne STC. However, Toronto Property Standards and many strata bylaws layer IIC 50 minimum on top, and most plan-examiners will reject a vertical multiplex floor-ceiling assembly that has no IIC consideration even if STC 50 is technically met.

Practical multiplex acoustic targets:

• Demising walls (between units, side by side): design STC 55 on the drawings to deliver STC 50 in the field.
• Floor-ceiling assemblies (between vertically stacked units): design STC 55 + IIC 55 minimum.
• Unit doors to public corridor: STC 30 minimum, achieved with solid-core door + perimeter seal.

The Existing Conditions Problem

A typical Toronto detached or semi built between 1920 and 1980 has these acoustic baselines:

• Existing demising walls (typical 2x4 with single layer plaster or drywall both sides, no insulation): STC 30-38.
• Existing floor-ceiling assemblies (2x8 or 2x10 joists, 3/4 hardwood + plaster ceiling): STC 35-42, IIC 25-35.
• Existing unit doors (often hollow-core or original solid-wood with no perimeter seal): STC 18-25.

Every one of these is below the OBC 9.11 mandate. The multiplex licensing renovation has to bring all of them up.

The Standard Toronto Multiplex Demising Wall Assembly

This is the assembly we use as the default on most 2026 multiplex projects in Toronto:

Wall assembly (lab STC 55-58, field STC 50-52 with normal workmanship):

• Existing 2x4 wood studs at 16" o.c.
• Strip drywall on at least one side; ideally both sides if access permits.
• Roxul Safe'n'Sound R-15 stone wool batts, full cavity.
• AcoustiClips (RSIC-1) or Resilmount A237R isolation clips on one side, hat channel between, at 24" o.c.
• Two layers of 5/8" Type-X drywall on the decoupled side, with Green Glue Noiseproofing Compound between (two tubes per 4x8 sheet, applied in random squiggle pattern).
• Single or double layer of 5/8" Type-X drywall on the opposite side. Single is usually adequate; double is used when both units are being renovated simultaneously and access permits.
• Gasketed electrical boxes (Lessco air-tight or Putty pads on standard boxes). Relocate any back-to-back boxes onto staggered stud bays.
• Acoustic sealant (OSI Pro-Series SC-175 or Tremco Acoustical) at every perimeter joint, every electrical box, every plumbing penetration.
• Acoustic sealant under the bottom plate during framing where the wall is being rebuilt.

This assembly also satisfies the OBC fire-separation requirement (1-hour rated when constructed with Type-X drywall in the listed assembly). Coordination with the fire-separation drawings is essential — see [Multiplex Fire Separation OBC Toronto](/blog/multiplex-fire-separation-obc-toronto).

The Standard Toronto Multiplex Floor-Ceiling Assembly

The vertical case is harder because impact noise (IIC) is added to the airborne STC requirement.

Floor-ceiling assembly (lab STC 55, IIC 55):

• Existing 2x8 or 2x10 joists.
• From below: strip ceiling drywall to expose joists.
• Pliteq GenieMat RST-02 or Maxxon Acousti-Mat resilient underlayment installed on the upper-unit subfloor surface, with engineered hardwood or vinyl plank above.
• New batt insulation (Roxul Safe'n'Sound R-23) in the joist cavity from below.
• AcoustiClips + hat channel on the underside of the joists.
• Two layers of 5/8" Type-X drywall as the new ceiling, with Green Glue between the layers.
• All ceiling fixtures (pot lights, smoke detectors) gasketed; use IC-AT rated sealed fixtures only.
• Acoustic sealant at every perimeter and penetration.

This assembly also satisfies fire-separation 1-hour rating with Type-X drywall.

Where the upper-unit floor cannot be lifted (tenants in place, finished hardwood being preserved), the underlayment-on-top portion is omitted and the assembly is rebuilt from below only. Outcome: STC 50-52 still achievable; IIC drops to roughly 45-50 — at or just below the de-facto target. Discuss with the plan-examiner before design.

Unit Doors

The unit-entry door is often overlooked and frequently fails inspection if specced as a standard interior door. The OBC requires the unit-to-corridor door to maintain the corridor's STC 30 minimum.

Acceptable unit door assembly:

• Solid-core door slab (mineral-core or premium solid-core, STC 30-33).
• Acoustic perimeter seal kit (top, both sides).
• Automatic door bottom (sweep that drops on closing).
• Standard fire-rated door if the corridor requires fire separation (most multiplex unit doors require a 20-minute or 45-minute fire rating; verify with the plan).

Material cost: $600-1,200 per unit door. Labour: $200-400.

Field STC Testing: When and Why

A field STC test (ASTM E336) by an acoustic consultant is required when:

• The plan-examiner specifically requests verification (rare; usually only when the as-built deviates from the listed assembly).
• The as-built construction does not match a published listing (custom assembly, novel material combination).
• A noise complaint after occupancy triggers a Property Standards investigation.

A typical Toronto field STC test costs $1,500-3,500 for a single partition. The acoustic consultant brings calibrated source and receiver equipment, sets up speakers and microphones in adjacent units, and measures transmission loss across the standard frequency bands.

For most multiplex projects, the published-listing path avoids the field test entirely. RenoHouse coordinates with consultants on the rare project where testing is required.

Coordination With Fire-Separation Scope

The same demising wall must satisfy:

• Acoustic STC 50 (this post).
• Fire-resistance rating (1 hour typical for multiplex demising walls; 45 minutes in some cases; see the dedicated fire-separation post).

The good news: the standard assembly above (Type-X drywall, stone wool, AcoustiClips, Green Glue) satisfies both in a single build. The drawings must reference both the STC listing and the fire-resistance listing for the same assembly. Most major listings (e.g., USG, CertainTeed published) cover both.

What does not satisfy both: a single layer of regular (non-Type-X) drywall, foam-insulation-only assemblies (no fire rating), and certain decoupling-only assemblies that lack mass for fire performance.

Realistic Budget for a Toronto Multiplex Acoustic Scope

For a typical detached-to-triplex conversion (2,400 sqft total, three units, roughly 600 sqft of demising wall + 1,200 sqft of floor-ceiling between units):

• Demising walls (Tier 2 standard assembly, both sides where possible): $8-12/sqft, total $5,000-7,200.
• Floor-ceiling assemblies (rebuild from below + underlayment from above): $15-25/sqft, total $18,000-30,000.
• Unit doors and seal kits (3 doors): $2,500-4,500.
• Acoustic sealant, gasketed boxes, perimeter detail (whole project): $1,500-3,000.
• Permit and plan review (acoustic portion): $500-1,500.

Total acoustic-specific scope: $27,500-46,000 for a typical triplex conversion. Often 8-12% of the total project budget.

Next Step

For pillar context see [Acoustic Soundproofing Renovation Toronto](/blog/acoustic-soundproofing-renovation-toronto-2026-complete-guide). For sibling scopes see [STC Rating Explained Toronto](/blog/stc-rating-explained-toronto-construction), [Green Glue vs Resilient Channel Toronto](/blog/green-glue-vs-resilient-channel-toronto), and [Floor Soundproofing Toronto](/blog/floor-soundproofing-toronto-impact-noise). For the fire-separation companion see [Multiplex Fire Separation OBC Toronto](/blog/multiplex-fire-separation-obc-toronto). Or book a multiplex consultation through the [home renovation service page](/services/home-renovation/acoustic-soundproofing-renovation).