Condo Flooring Sound Rating: IIC, STC and Board Approval in Toronto

A condo flooring sound rating tells your board how much noise a floor lets through to the suite below. Most Toronto condo boards set a minimum IIC (Impact Insulation Class) for footsteps, and some also cite STC (Sound Transmission Class) for voices and music. The rating belongs to a tested assembly, meaning the floor, underlay, slab and ceiling together, so the underlay’s test report is the document that wins or loses approval.

If you are still choosing a material, start with our guide to which floors suit a Toronto condo slab. This post picks up where that one ends: what the numbers mean, why lab and field results differ, how tile changes the picture and which papers get a flooring application approved on the first round.

What is the difference between IIC and STC?

Both ratings describe how well a floor-ceiling assembly blocks sound. They measure different kinds of sound, and a flooring change affects one far more than the other.

IIC measures impact sound

Impact sound starts as a strike on the floor: footsteps, a dropped pot, a chair dragged across the room. In a lab, a standard tapping machine hits the floor while microphones in the room below record the result, following ASTM E492, and the reading is turned into a single number under ASTM E989. A higher IIC means less noise reaches your neighbour. Because the strike lands on your floor, the floor covering and the underlay beneath it change IIC more than anything else you control.

STC measures airborne sound

Airborne sound travels through the air before it hits the structure: voices, a television, music. STC comes from lab tests under ASTM E90, rated under ASTM E413. In a concrete tower, the mass of the slab and the ceiling below do most of the work against airborne sound, so swapping carpet for plank seldom moves STC by much. When a board quotes STC in its flooring rule, it is often repeating language from the building’s original design.

Read the exact wording of your building’s rule. A rule that names a lab IIC, a field FIIC or a ΔIIC is asking for three different kinds of evidence, and an underlay report that answers one may not answer the others.

What does a tested assembly mean for condo flooring?

A sound rating never belongs to an underlay on its own. It belongs to the full build-up in the test: the floor covering on top, the underlay, a concrete slab of stated thickness and the ceiling under it, which may be bare concrete or a suspended drywall ceiling. Change one layer and the number changes.

A suspended ceiling with insulation in the cavity adds a lot to an impact rating. An underlay tested over that kind of ceiling can post a high IIC, and the same underlay over a bare concrete ceiling, common in Toronto towers, will score lower. Neither result is wrong. They describe different buildings.

What to check on a sound test report

• The test standard: ASTM E492 and E989 for IIC, ASTM E90 and E413 for STC.
• The lab: an independent acoustical lab, named on the report.
• The floor covering used in the test: vinyl, laminate, engineered wood or tile, and its thickness.
• The slab thickness and whether the ceiling below was bare or suspended.
• The product name, matching the underlay on your quote.

Why the floor on top still matters

A report run with laminate on top tells you little about porcelain tile, and a thin glue-down vinyl will not test like a thick rigid-core plank. Ask for a report that pairs the underlay with a covering close to the one you plan to install. Our crews fit the IIC 72 certified underpad under both laminate plank installs in condo suites and rigid-core vinyl jobs on concrete where a building calls for it. For the trade-offs between those two floors, read our laminate and vinyl comparison.

Why do lab and field sound ratings differ?

A lab isolates the floor sample, so sound has one path to the microphone. In a finished building, sound also travels sideways through walls, columns, pipes and cabinets, which acousticians call flanking. A field test measured under ASTM E1007 captures all of it, and field results often come in below the lab number for the same product.

That gap is why the details of the install matter as much as the underlay. A National Research Council paper on controlling impact sound through floors points out that the National Building Code sets no requirement for floor impact sound. Your condo’s own documents fill that gap, and a floor that tests well in a lab can still draw complaints if it is installed with shortcuts.

Install details that protect the field rating

• Leave the perimeter gap open. A floating floor that touches the wall passes impact into the structure.
• Keep trim off the floor. Nail baseboard and quarter-round to the wall, not down through the plank.
• Run the underlay without gaps, with seams taped as the maker instructs.
• Avoid fasteners through the underlay into the slab at transitions and thresholds.
• Isolate fixed items such as kitchen islands and bathroom vanities as the underlay guide shows.

What sound mat goes under condo tile?

Porcelain and ceramic tile are hard and thin, which makes them the loudest finish for the suite below. Most boards that allow tile ask for an acoustic membrane bonded to the slab, with the tile set in mortar on top. The membrane needs its own test report, run with tile on top, and the same rules apply: check the slab, the ceiling and the covering in the test.

Grout and mortar can bridge the membrane at the walls and create a direct path for sound. Installers keep a gap at the perimeter and fill it with a flexible sealant instead of grout. In bathrooms, the tub, toilet and vanity sit on the membrane or get their own isolation, depending on the product guide.

How does condo board approval for new flooring work?

The steps vary by building, but most Toronto boards follow a pattern. The Condominium Authority of Ontario notes that the Condo Act bars unreasonable noise whatever a building’s documents say, and that noise rules are most likely found in the declaration or rules. Start there.

1. Read the declaration and rules. Note the rating, the test type and any approved underlay list.
2. Ask the property manager for the alteration form. Some buildings also ask owners to sign an alteration agreement.
3. Collect the data sheets for the floor covering and the underlay or membrane.
4. Attach the sound test report that comes nearest to your own assembly.
5. Add the contractor details: company name, insurance certificate, work dates and hours.
6. Book the service elevator for delivery and debris once approval comes through.
7. Wait for written approval before material arrives or the old floor comes up.

Property managers see many incomplete applications, and each missing page restarts the wait. A contractor who has done condo work can tell you what your building asked for last time. Our guide to hiring a flooring contractor lists the questions to ask about board paperwork. We install in towers across the GTA, from North York flooring projects near Yonge and Sheppard to flooring installation in Mississauga high-rises.

How do you avoid a noise dispute after the floor goes in?

Keep a file. Store the board’s written approval, the data sheets, the test report and the installer’s invoice with your unit records. If a neighbour complains months later, those papers show you followed the rule, and a buyer’s lawyer may ask for them when you sell.

Daily habits matter too. Felt pads on chair and table legs, rugs in the living room and soft-soled slippers cut a large share of impact noise. If a complaint does arrive, talk to the neighbour first. Disputes that go further can end up at the Condominium Authority Tribunal, so a calm conversation and a copy of your approval are worth a lot early on.

Sound rating questions