Acoustic Underlayment for Flooring: A Canadian Buyer's Guide (2026)

By Max, manager of YaleTown Floor · Updated September 1, 2026 · 14 min read

Acoustic underlayment is the cheapest part of a flooring job and the one most likely to cause a warranty claim. The reason is simple: underlay does five jobs, and almost everyone buys it for one. Sound is the headline, but the same thin sheet is also controlling moisture off your slab, smoothing the subfloor, supporting the click joint that holds your floor together, and insulating your radiant heat whether you wanted it to or not. Get the sound rating right and the compressive strength wrong and the floor fails at the joints in three years. This guide covers all five jobs, the four materials, and the real specs and pricing on every underlay we stock. For the condo bylaw side — IIC numbers, board approvals, test reports — see our condo and strata flooring rules guide, which handles that in full.

Cork Plus 600 — 6 mm natural cork. Dense, dimensionally stable, and it holds its thickness under furniture for decades.

The Five Jobs Underlayment Does

Before any product comparison, this is the frame that makes the rest of the decision obvious. A sheet of underlay under a floating floor is doing all of the following at once:

Jobs 1 and 4 pull in opposite directions, and that tension is the single most useful thing to understand about this category. Soft and thick is quiet. Firm and thin protects the joint. Every underlay is a compromise between those two, and the right compromise depends on your floor and your building — not on which product has the biggest number on the packaging.

Job 1 — Impact Sound

Impact sound is footsteps, dropped objects and chairs dragged across a floor, transmitted as vibration into the structure and re-radiated into the space below. The underlay's job is to absorb that energy before it reaches the slab.

The rating you will see is IIC (Impact Insulation Class), sometimes alongside STC (Sound Transmission Class, which covers airborne noise like voices). Two things are worth knowing here and then we will hand you over to the detailed guide: an IIC number belongs to a tested assembly, not to the underlay on its own, and no Canadian building code sets a minimum IIC for your floor — every number your building enforces comes from its own bylaw.

Our range spans IIC 63 to IIC 92. If you are working to a specific number for a condo board, the ratings table, the approval process and the test-report question are all covered in Condo and Strata Flooring Rules in Canada. The rest of this guide is about everything else the underlay has to do.

Job 2 — Moisture and Vapour Control

Concrete is never finished releasing moisture. A slab poured a decade ago still transmits water vapour upward, and in a Canadian basement the ground around that slab is saturated for part of every year. Put a floor over it with no vapour control and the moisture has nowhere to go but into your flooring assembly.

Underlays handle this in one of two ways. Some have an integrated vapour barrier — a bonded film with a taped overlap flap. Others are permeable and require a separate 6 mil polyethylene sheet laid first, seams taped. Of the underlays we stock, the Richmond Silent Performer and Richmond Quiet Block both incorporate a moisture barrier.

Job 3 — Subfloor Smoothing, and Its Limits

Underlay evens out the fine texture of a subfloor: the grain of plywood, the light roughness of a power-trowelled slab, a slightly proud fastener head. That is genuinely useful and it is why bare-subfloor installations look worse over time.

What it does not do is fix a subfloor that is out of tolerance. Manufacturers typically specify flatness within about 3 mm over 2 m, and no underlay changes that number. A soft mat laid over a real dip simply drapes into it, creating a void. Walk across that void a few thousand times and the click joint above it works loose.

The rule we use: if a 2 m straightedge rocks or shows daylight beyond roughly 3 mm, the floor is not ready and underlay is not the fix. Self-levelling compound is.

Job 4 — Supporting the Click Joint

This is the job nobody buys underlay for and the one that causes the most failures.

A floating floor is a single sheet of interlocked planks resting on the underlay. Every step deflects it slightly. If the underlay is too soft or too thick, that deflection concentrates at the click joints — the weakest point in the assembly — and repeated flexing works them apart. The symptoms arrive slowly: a hollow sound, then visible gapping at the end joints, then planks that will not stay locked.

This is why rigid-core vinyl manufacturers specify a maximum underlay thickness, commonly in the 1 to 3 mm range, and a minimum compressive strength. It is also why the thickest, softest, highest-IIC mat is frequently the wrong answer for an SPC floor. If you are installing rigid core, read our SPC guide alongside this one — the joint is the part that fails.

Job 5 — Thermal Resistance and Radiant Heat

Every underlay is an insulator. Usually that is a small bonus — a slightly warmer floor underfoot. Over radiant heating it is a problem.

Underlay sits between the heating element and the room, and its R-value directly reduces how much heat reaches you. Most radiant manufacturers specify a maximum total R-value for everything above the element, counting the underlay and the floor together. Exceed it and the system runs hotter to compensate, which can push the floor past its own temperature ceiling.

Published R-values in this category are sparse — the Richmond Quiet Block lists R-0.225, which is typical for a thin product. The practical rule over radiant heat: choose the thinnest, densest underlay that satisfies your other requirements, and check the flooring and heating manufacturers' combined limit before ordering. Thick foam is the wrong choice here.

Richmond Silent Performer — 2 mm with an integrated moisture barrier. Thin and dense, which is what radiant heat and rigid-core joints both want.

The Four Materials Compared

Memory-foam and hybrid products sit between these categories. The material tells you how the underlay will behave in year ten, which is the part a spec sheet rarely captures: foam that has flattened under a sofa is no longer doing job 1 or job 4.

Floor tek Super Silencer — 4.5 mm of hybrid foam. High acoustic performance where build height is limited.

Compressive Strength — The Spec Nobody Quotes

Compressive strength is how much load an underlay carries without permanent deformation. It is the number that decides whether job 4 succeeds, and it is almost never printed on Canadian retail packaging — ours included, which is a gap worth naming.

You can reason about it from material and density even without a figure. Cork and rubber are high. IXPE is moderate and predictable. Standard foam is low, and low is where floating floors get into trouble. If two underlays are the same thickness and one costs a third as much, the difference is almost always density.

When it matters most: heavy furniture on a floating floor, kitchen islands, pianos, and any rigid-core installation. Ask your supplier for the compressive figure and the manufacturer's maximum thickness — we will supply both for anything we sell.

Memory foam underlayment — comfortable underfoot, but check the flooring manufacturer's compressive-strength minimum before using it under a rigid-core floor.

Attached Pad vs Separate Underlay

Most rigid-core vinyl and a growing share of laminate now ships with a factory-bonded pad, usually 1 to 1.5 mm of IXPE or cork. It is engineered as part of the floor, tested with it, and warranted with it.

In most cases you should not add a second underlay beneath an attached pad. The combined thickness is exactly the condition that lets the click joint flex, and many manufacturers prohibit it outright. The common exception is a condo where a bylaw demands a rated assembly the attached pad cannot reach on its own — and even then, the flooring warranty has to permit it, which is a question to settle before you order rather than after.

Every Underlay We Stock, by Material

Eleven underlays, sorted by what they are made of and what they do. Sound ratings for the same products are tabled by IIC and STC in our condo and strata guide — this table is about material, thickness and function.

Browse the full underlayment range, the acoustic underlayment collection, the waterproof underlayment range, or the QuietWalk products specifically.

Which Underlay for Which Floor

When Underlay Is Not the Answer

If the subfloor is out of tolerance, no underlay saves it. The fix is self-levelling compound, poured to create a flat plane before anything else goes down. It is not an exotic product and it is far cheaper than relaying a failed floor.

Coverage depends on depth, so budget by the bag rather than by the square foot. As a planning figure, allow $1 to $3 per square foot installed for levelling where it is needed — the same range we quote in our flooring installation cost guide.

Mapei Ultraplan 1 Plus — quick-setting self-levelling compound. When the straightedge rocks, this is the fix, not a thicker underlay.

Ardex V 1000 — $36.99 for 50 lb. Levelling compound is the fix for an out-of-tolerance subfloor; underlay is not.

What It Costs

Underlayment is the cheapest line on a flooring quote and the worst place to save money. Our range runs $0.39 to $2.29 per square foot, and most residential projects land between $0.39 and $0.69.

Against a floor at $2.59 to $5.49 per square foot plus labour, even the most expensive underlay we sell is a modest share of the job — and it is the component protecting everything above it.

Installation

• Run the rolls in the same direction as the planks, so seams never coincide with a long plank joint.
• Butt the seams, do not overlap — unless the product has a purpose-made overlap flap and tape. Overlapping a butt-seam product creates a ridge that telegraphs through the floor.
• Tape every seam where the underlay is doing vapour-barrier duty. An untaped seam is a hole in the barrier.
• Stop the underlay at the wall, not up it. Running it behind the baseboard creates a rigid bridge that undoes the acoustic benefit.
• Lay only what you can cover that day. Underlay left exposed collects grit and gets walked on, and compressed underlay does not recover.

Five Expensive Mistakes

• Buying on the sound rating alone. The highest-IIC mat is often the wrong compressive strength for a rigid-core floor.
• Adding underlay beneath an attached pad. Usually prohibited, and it is the classic cause of joint failure.
• Using underlay to hide an uneven subfloor. It creates a void, and the void becomes a failure.
• Skipping the vapour barrier on a slab. The cheapest omission with the most expensive consequence.
• Thick foam over radiant heat. The system never reaches setpoint and gets run hotter to compensate.

Full-Service vs. Supply-Only — What We Offer

Why Trust YaleTown Floor on Underlayment?

We sell eleven underlays and we turn down the sale on roughly one in ten because the customer's floor will not tolerate the mat they have chosen. That is the useful thing we can offer here: the underlay is the part of the assembly where the cheapest decision and the correct decision are most often different, and where the failure shows up years later in the click joints rather than immediately. We will confirm the flooring manufacturer's maximum thickness and minimum compressive strength for any floor we sell, and supply the test report for any underlay in the range.

Frequently Asked Questions

What does acoustic underlayment actually do?

Five things: impact sound reduction, moisture control, subfloor smoothing, click-joint support and thermal resistance. Sound is only one. Choosing on the sound rating alone is how people end up with an underlay that voids the flooring warranty.

Do I need underlayment if my flooring has an attached pad?

Usually not, and often you must not. Attached pads are engineered and warranted as part of the floor, and many manufacturers prohibit a second underlay beneath them. The exception is a condo bylaw requiring a rated assembly — and the flooring warranty still has to permit it.

What is compressive strength and why does it matter more than thickness?

It is how much load the underlay carries without permanently deforming. Too soft and the floating floor flexes at the click joints, which works them apart over time. Rigid-core manufacturers specify both a maximum thickness and a minimum compressive strength.

Which underlayment is best for concrete slabs?

One with an integrated vapour barrier, or a separate 6 mil poly sheet under a permeable underlay. Test the slab first — if readings are high, no underlay solves it and the slab itself needs addressing.

Can I use underlayment over radiant in-floor heating?

Yes, but keep R-value low. Underlay insulates, and most radiant manufacturers cap the total R-value above the element. Choose the thinnest, densest product that meets your other requirements.

What is the difference between foam, IXPE, cork and rubber underlayment?

Foam is cheapest and compresses permanently. IXPE is cross-linked closed-cell, thin and compression resistant — the rigid-core standard. Cork is dense and holds its thickness for decades. Rubber gives the best impact performance per millimetre but is heaviest and dearest.

How thick should flooring underlayment be?

Thinner than most people assume — 1 to 3 mm for rigid-core vinyl, 2 to 3 mm for laminate. Thicker 6 to 8 mm mats exist for condo acoustic requirements but must be matched to a floor rated to sit on them.

Does underlayment fix an uneven subfloor?

Only minor texture. Manufacturers specify flatness within about 3 mm over 2 m and underlay does not change that. Anything worse needs self-levelling compound, which runs $36.99 to $76.99 per 50 lb bag in our range.

How much does flooring underlayment cost in Canada?

$0.39 to $2.29 per sq ft across our range, with most residential projects at $0.39 to $0.69 — roughly $390 to $690 on a 1,000 sq ft floor.

Which way do you lay underlayment seams?

Same direction as the planks, butted rather than overlapped unless the product has an overlap flap. Tape every seam so the vapour barrier stays continuous, and stop the underlay at the wall rather than running it up behind the baseboard.

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Shop the Collections

• All Flooring Underlayment — the full range
• Acoustic Underlayment — IIC 63 to IIC 92
• Waterproof Underlayment
• QuietWalk Underlayment
• Mapei Levelling Compounds
• SPC Vinyl Flooring
• Laminate Flooring
• Engineered Hardwood

Related Reading

• Condo and Strata Flooring Rules in Canada: IIC, STC and What Boards Actually Require
• What Is SPC Flooring? The Complete Canadian Guide (2026)
• The Essential Guide to Vinyl Flooring Underlayment
• Underlayment Flooring — Options, Need and Benefits
• Flooring Installation Cost in Vancouver & Canada 2026