Most of the time, no. If your vinyl plank already has a pad attached to the back, which most quality click-lock planks do, you do not need a separate underlayment under vinyl plank flooring, and adding one can actually cause problems. That is the honest short answer. The longer answer is about the few real exceptions: bare concrete, condo sound rules, and glue-down floors. Knowing which situation you are in saves you money and protects your warranty.
This guide is written by Caledon Floors, a Canadian hard-surface flooring distributor based in Vancouver, BC. We are going to walk through what underlayment actually does, why most WPC vinyl flooring already includes it, when you genuinely need a separate layer, and the one mistake that quietly voids more warranties than almost anything else.
Do you need underlayment under vinyl plank flooring?
It depends on two things: the plank and the subfloor. The plank decides whether the cushioning is already built in. The subfloor decides whether you need a moisture or sound layer on top of that. Get both answers and you know exactly what to buy.
Most modern click-lock vinyl planks, especially WPC, come with an attached pad bonded to the underside. That pad is the underlayment. A bare plank with no attached pad, or a glue-down floor, is a different story and may need a separate layer. So the first thing to do is flip a sample over and look at the back.
What does underlayment actually do?
Underlayment is the thin layer between your subfloor and your flooring, and it does a few specific jobs. It adds a little cushioning underfoot, dampens sound, smooths very minor subfloor imperfections, and, with the right type, acts as a moisture or vapour barrier over concrete.
It is just as important to know what underlayment does not do. It does not make a floor waterproof. The waterproof part of waterproof flooring is the plank itself, the core and the wear layer, not the pad beneath it. Underlayment also cannot fix a subfloor that is out of level or full of bumps. That is a subfloor prep job, and skipping it causes failures no pad can hide. You can read more in our guide to subfloor preparation mistakes.
Why most WPC vinyl flooring already has it built in
A pad-attached floating floor is the reason this question trips so many people up. WPC planks use a stable composite core, and the better ones bond a comfort pad to the back at the factory. That attached pad is your underlayment, already matched to the plank and already accounted for in the warranty.
Caledon's WPC collections all ship this way. Goliath and Artimis carry a 1.5mm IXPE attached pad, and Monolith carries a 1.5mm EVA pad. These are click-lock floating floors, which means they lock together and rest over the subfloor with no glue and no separate underlay. If you want the background on how that construction works, our WPC vinyl flooring primer covers it, along with our click-lock installation guide.
Can you add underlayment under a floor that already has a pad?
No, and this is the mistake to avoid. Stacking a separate underlayment under a plank that already has an attached pad gives the floor too much cushion. The floor flexes more than it was designed to, and that flex goes straight into the click joints that hold the planks together.
Over time, too much give causes the locking edges to stress, separate, and gap. It is one of the most common causes of a floating floor failing, and because it goes against the installation instructions, it usually voids the warranty. More padding feels like it should be better. With a click-lock floor, it is not. If your plank has a pad, the pad is the underlayment, full stop.
When you do need a separate underlayment
There are real exceptions, and they are worth taking seriously. The table below is the quick version, and the sections after it explain the two that matter most in Canadian homes.
| Your situation | Separate underlayment? |
|---|---|
| Click-lock plank with an attached pad, over a sound wood subfloor | No, the pad is enough |
| Click-lock plank with no attached pad (bare SPC or budget LVP) | Often yes, a thin compatible pad for comfort and sound |
| Any floating floor over a concrete slab or basement | Usually a vapour barrier, even with an attached pad |
| Condo with a strata sound requirement | Often an acoustic layer or a rated assembly, check the bylaw |
| Glue-down or dryback vinyl | No pad, the plank is bonded directly to a prepped subfloor |
Underlayment over concrete: the Canadian basement question
Concrete is the exception most Canadian homeowners run into, because so many of our basements and condos sit on a slab. Concrete looks dry, but it constantly wicks moisture vapour up from the ground, and that vapour needs somewhere to go before it reaches your floor.
Here is the nuance. An attached comfort pad is not automatically a vapour barrier. Some include a moisture film, many do not. Over a slab, the usual approach is a 6-mil polyethylene sheet under the floor to block vapour, even when the plank already has a comfort pad, because the poly is doing a different job than the pad. Always check the manufacturer's instructions for your specific plank, since the right assembly depends on the product. Our guide to moisture and vapour barriers walks through this, and our best flooring for Canadian basements guide covers the slab question in more detail.
Underlayment and condo sound rules
Condos are the other place this comes up, because most buildings have a strata bylaw that sets a minimum sound rating for flooring. The ratings to know are STC, which measures airborne sound like voices, and IIC, which measures impact sound like footsteps. Your neighbour below cares a lot about that second one.
A thicker WPC plank already helps here. Caledon's Monolith collection, for example, is rated STC 71 and IIC 73. Even so, your building may require a specific underlayment or a tested floor assembly to meet its bylaw, and you generally cannot just stack an acoustic mat under a pad-attached plank without creating the flex problem above. The right move is to read your strata's flooring rules first, then choose a plank and an approved assembly that meets the number. Our condo flooring sound and underlayment guide goes deeper on ratings and bylaws.
What about glue-down and bare SPC planks?
Glue-down vinyl skips underlayment entirely. The plank is bonded directly to the subfloor with adhesive, so there is no floating layer and no pad. What it needs instead is a clean, flat, properly prepped subfloor, because every imperfection telegraphs straight through.
Bare SPC planks, the thin rigid ones with no attached pad, are the one case where a separate thin underlayment can genuinely help. SPC is harder and louder underfoot than WPC, so a thin compatible pad, no more than the manufacturer allows, adds comfort and quiet. The key word is compatible. Use the thickness the maker specifies and nothing more, because the same over-cushion rule still applies.
Frequently asked questions
A few quick answers to the questions Canadian homeowners ask most about underlayment for vinyl plank flooring.
How do I know if my vinyl plank has an attached pad?
Flip a sample over. An attached pad is a foam or felt-like layer bonded to the back of the plank, usually a soft grey or white. If the back is just the hard composite core, there is no attached pad. The product spec sheet will also list it, often as IXPE or EVA.
Does underlayment make vinyl plank waterproof?
No. The waterproofing comes from the plank's core and wear layer, not the pad. A vapour barrier under the floor protects against moisture rising from concrete, but it is not what makes the surface waterproof.
Can I use the same underlayment as laminate?
Not always. Laminate underlayments are often thicker than vinyl allows, and too much thickness is exactly what stresses vinyl click joints. If your vinyl plank needs a separate pad, use one rated for vinyl at the thickness the manufacturer specifies.
Do I need underlayment over plywood or OSB?
Usually not, if your plank has an attached pad and the subfloor is sound and flat. Wood subfloors do not have the moisture issue concrete does, so the attached pad is generally all you need.
The honest bottom line
For most homeowners buying a quality click-lock floor, the underlayment question answers itself: it is already attached, and adding more works against you. The exceptions are specific and easy to spot once you know them. A concrete slab usually wants a vapour barrier, a condo wants you to read the bylaw first, and a glue-down or bare SPC floor follows its own rules. Match the layer to your plank and your subfloor, and you protect both your floor and its warranty.
If you are not sure what your subfloor needs or which plank suits your space, a good dealer can look at your situation and tell you straight. You can reach the Caledon Floors team here for honest, no-pressure guidance.
To find waterproof vinyl flooring in Canada, click here for a Caledon Floors dealer near you.
