STC and IIC: what your condo board is actually asking for

If you own a condo in Toronto, Vancouver or Montréal, your flooring decision has a gatekeeper. Somewhere in the declaration, the rules or the renovation application there is a number — usually an IIC, sometimes an STC — and a floor that does not satisfy it can be ordered out at your expense long after it is down.

Satisfying it is not the hard part. What trips people up is that the number does not belong to the product. It belongs to the whole floor-and-ceiling assembly, and the rating printed on an underlay box was measured over somebody else’s slab, under somebody else’s ceiling.

Two ratings, two different noises

Higher is better in all of them, and the points behave roughly like decibels: five points is plainly audible, one point is a marketing claim.

What the code requires — and what it does not

The National Building Code of Canada sets an airborne requirement between dwelling units; since the 2015 edition that is expressed as an apparent sound transmission class measured in the building, with the older laboratory STC route retained as an alternative. Provinces adopt the national code on their own timetable and with their own amendments, so the edition governing your building is the provincial one.

What the Code does not do is set a mandatory impact requirement. Footfall — the complaint that actually generates neighbour disputes and legal letters — is left to guidance rather than regulation. That gap is exactly why condo corporations write their own flooring rules, and why your number comes from the board rather than from a building inspector.

What boards typically ask for

Every corporation is different and only your own documents bind you. That said, the requests fall into recognisable shapes:

• A minimum IIC, commonly in the 50–55 range, sometimes paired with an STC minimum.
• A minimum ΔIIC for the covering instead — the more honest ask for a retrofit, because it isolates what your floor contributes rather than crediting you for the building’s slab.
• A named underlay, or a list of approved ones. This removes the argument and also removes your choice.
• A limit on hard surface — bedrooms excluded, or a stated proportion of the floor covered by area rugs afterwards.
• Documentation before work starts: the data sheet, the acoustic test report, an installer’s declaration, proof of insurance, an elevator booking and permitted hours.

Get the requirement in writing from the property manager, and get the wording, not a summary. “IIC 55” and “ΔIIC 20” are different tests, and a floor that satisfies one can fail the other outright.

Why the number belongs to the assembly, not the product

An impact rating describes one specific stack of materials, and changing any layer changes the result — usually by more than the underlay you are agonising over could ever move it.

• The slab. Six inches of normal-weight concrete is the usual reference in published tests. Eight inches performs differently, and hollow-core precast differs again.
• The ceiling below you. Gypsum on resilient channel with an air space is frequently worth more points than any floor covering. A slab with paint on the underside is the hard case, and it is common in older buildings.
• The covering. Carpet over an underpad passes an impact test easily and does little for airborne noise. Hard surface is the opposite problem, which is why the rules exist at all.
• The perimeter. A floating floor touching a wall, a pipe, a door frame or a baseboard nailed through it has a flanking path, and a flanking path spends the points you paid for.

This is why laboratory and field numbers diverge. A field result to ASTM E1007 commonly lands several points below the laboratory IIC for a nominally identical assembly, because laboratories are built to eliminate flanking and buildings are not. If your board’s number is a lab IIC, you can satisfy it on paper and still hear the neighbour’s dog.

How to read a manufacturer’s tested assembly

A genuine test report tells you what was tested. If you cannot answer all six of these from the document in front of you, it is a marketing number rather than a rating:

1. The standard cited — E492 with E989 for laboratory IIC, E1007 for a field result, E2179 for delta IIC, E90 with E413 for STC. No standard named, no rating.
2. The laboratory and the report number, with a date. A board’s engineer will ask for exactly this.
3. The slab: thickness and type, stated explicitly.
4. The ceiling: “none”, “gypsum applied directly”, “resilient channel with two layers of 5/8 in gypsum”. This line moves the result more than the underlay does.
5. The full covering as tested — which plank, which underlay, which thickness. A result obtained with 2 mm rubber does not transfer to 1 mm foam.
6. Whether the figure is IIC or ΔIIC. A delta of 20 and an IIC of 20 are not remotely the same claim, and confusing them is the commonest error in this whole subject.

The red flags are the mirror image: a large number with no assembly described, a decibel-reduction claim citing no standard, a rating quoted for a collection rather than a specific plank-and-underlay pairing, and a laboratory figure presented as what you will get in your unit. Where a manufacturer publishes a tested assembly for a product we list, that document is what your board wants to see rather than a screenshot of a web page — ask us for it on the product you are shortlisting, early enough that the answer can still change your mind.

What actually raises the number

Four levers, in rough order of how much they move the result. Note that the covering is last:

1. Decoupling the ceiling below. Resilient channel, an air space, mass on the underside. Usually somebody else’s ceiling, and therefore not available to you.
2. Mass. A concrete or gypsum topping, where the building allows the load and your headroom allows the height.
3. Resilience under the floor. The acoustic underlay — the lever most owners actually have, and where a dense rubber mat earns its price.
4. Airtight isolation at the edges. Expansion gap maintained, no fastener bridging floor to wall, baseboard fixed to the wall only, acoustic sealant in the gap, penetrations sleeved rather than grouted solid.

Floating installations are the condo default for this reason — a resilient layer can only exist under a floor that is not bonded to the slab. Our catalogue publishes a floating method on 3,884 products and click-lock on 2,498, though those tags overlap rather than partition and cover only listings where a method is published. The method makes an acoustic build possible; it does not make it compliant. That is still the assembly’s job.

The order of operations that saves money

1. Get the rule in writing, with the exact test and the exact number.
2. Shortlist plank-and-underlay pairings that have a published test report matching that test.
3. Submit for approval, and get the approval in writing, before you order anything.
4. Then order — floor, underlay, transitions and trims together, on one shipment.
5. Book the elevator, confirm hours and insurance, and check your door undercuts and balcony sill against the finished build-up height.

That order matters because ordering first and asking afterwards can leave you holding material you are not permitted to install. Returns are accepted within 30 days for unused product in its original packaging, with full refunds where a product is faulty or damaged; change-of-mind returns are not accepted. A 15% restocking fee may apply once your refund assessment has been completed, though no restocking fee applies to faulty or warranty returns — and return shipping is yours to pay, with shipping costs non-refundable. Sending a pallet back across the country is not a small line, which is the best argument there is for getting the board’s answer first.

Shop what this guide covers

• underlayment — the one lever in that list of four you actually control. Ask us for the tested assembly on any product before you order.
• engineered hardwood and vinyl planks (LVP and SPC) — the two floating-capable floors a board is most likely to be looking at.
• caulk and sealants — acoustic sealant at the perimeter, which is where the points you paid for get spent.
• mouldings and trims — transitions that let the floor move instead of pinning it.
• The underlay guide — thickness, density and the mistakes that void a warranty.