Here’s something we see constantly during installations: homeowners spend weeks researching LVP colours, textures, and brands, then spend about thirty seconds on underlayment. Some skip it entirely, while others double up without realising the floor already has built-in padding.
Both mistakes cause real problems. Shifting planks. Hollow sounds underfoot. Squeaks that show up six months later. And in some cases, a voided warranty.
The layer underneath your floor isn’t an afterthought. It determines how stable, quiet, and long-lasting your floor actually is. Get it right, and you won’t think about it again. Get it wrong, and you’ll feel it every time you walk across the room.
Table of Contents
Does Your LVP Already Have Underlayment?
Flip a plank over before you buy anything. If there is already a foam or cork layer attached to the back, your floor already includes underlayment. Many modern LVP products do.
Adding another layer on top is the most common installation mistake we see. Too much padding softens the floor and puts constant stress on the locking joints. Eventually, they give. The floor starts moving when it shouldn’t.
One exception: Installing over concrete still requires a 6-mil poly vapour barrier even when the planks have built-in padding. The foam backing doesn’t handle ground moisture on its own. That’s a separate problem requiring a separate solution.
What Does Underlayment Actually Do?
Not just smoothing the surface. Five things all affect how the floor performs over time.
- Sound Absorption: kills footstep noise before it travels between floors. In a multi-story home or condo, this one matters more than most people expect until they’ve lived without it.
- Moisture Blocking: Stops vapour from rising through concrete and reaching the planks. Miss this step in the wrong room, and mould is the outcome.
- Comfort Underfoot: A small amount of cushion that adds up fast when you’re on your feet all day in a kitchen or standing at a laundry room sink.
- Subfloor smoothing: Fills minor dips and imperfections so planks sit level. Hard limit here, though: underlayment cannot fix a bad subfloor. Needs to be flat within 3/16 inch over a 10-foot span before anything goes down.
- Floor Stability: Reduces movement and takes pressure off locking joints. Keeps everything where it’s supposed to be.
Types of LVP Underlayment
1. Foam Underlayment
Cheapest option. Light cushioning cuts some walking noise. Doesn’t block moisture. Never use foam alone over concrete.
Best for: Bedrooms, living rooms, upper floors with no moisture risk. That’s where foam belongs.
2. Cork Underlayment
Mould-resistant naturally. One of the best sound absorbers available. Eco-friendly. If noise between floors is the main concern for condos, multi-level homes, and upper-floor rooms, cork is usually the right answer.
Still needs a vapour barrier underneath in kitchens and bathrooms. Cork handles sound, not ground moisture.
3. Rubber Underlayment
Best soundproofing of the bunch. More durable than foam or cork, it takes heavy furniture without compressing, and holds up in high-traffic spaces. Also, the most expensive.
Best for: Home gyms, heavy-use rooms, and anywhere furniture gets moved around regularly.
4. Felt Underlayment
Better sound insulation than basic foam. Some versions include a vapour barrier already built in. Works well on upper floors in multi-story homes, a solid middle-ground option.
Best for: Upper floors of multi-story houses.
5. Vapour Barrier Underlayment
Not optional over concrete. A vapour barrier prevents moisture from rising through the slab and damaging LVP from underneath.
Basement or concrete slab installations require vapour barrier underlayment, with no exceptions. Bathrooms also need proper moisture protection because moisture can come from both above and below. In most cases, a combination underlayment with a built-in vapour barrier is the correct solution.
6. Combination Underlayment
Foam or cork with a built-in vapour barrier in one product. It handles both cushioning and moisture protection, making it a practical choice for many installations.
It is especially suitable for concrete subfloors, basements, kitchens, and bathrooms where moisture control is important. It also provides a layer of thermal insulation, which helps reduce the cold feel of concrete floors in winter, although it does not replace proper heating.
Radiant Heated Floors
Thick underlayment with a high R-value can block heat from reaching the surface. That defeats the whole system. For radiant heating, always go thin, always go low R-value, and confirm your LVP manufacturer specifically approves it before anything goes down.
Check Moisture Before Installation
Don’t guess on concrete. Tape plastic sheeting tightly to the floor, leave it for 24 hours, then lift it. Condensation on the underside of the moisture is present. Vapour barrier required. No working around it.
The 3mm Rule
Manufacturers are strict here. Total underlayment thickness never above 3mm.
- LVP with built-in pad: 0mm additional (vapour barrier only, if over concrete)
- LVP without pad: 2mm to 3mm is the right range
- Above 3mm: joint stress, gaps open, warranty likely void
Thicker is not better. It’s actually worse.
Matching Underlayment to Your Subfloor
Concrete Subfloor
Moisture control first. 6-mil vapour barrier, standalone or built into a combination underlayment. Without it, moisture coming up through the slab eventually damages the planks from below.
Plywood or Wood Subfloor
Foam, cork, or rubber all work well based on the room and budget. For LVP underlayment on a wood subfloor specifically, cork is the most common recommendation, as it handles minor surface variation well and adds sound absorption without thickness issues.
Over existing tile or vinyl
Thin foam or cork to smooth minor surface irregularities. Watch the thickness-raising floor height here, which creates transition problems at doors and edges.
Floating vs Glue-Down
Floating
Planks click together, sit above the subfloor, not fastened to it. Underlayment is essential. Foam, cork, or rubber, depending on the room.
Glue-Down
Planks are bonded directly to the subfloor. Underlayment is generally not used. Foam underneath a glue-down floor stops proper adhesion, and planks pull apart. Some premium luxury vinyl flooring products allow a very thin sound layer, but check the manufacturer’s guide before assuming.
Not sure which method you’re using? Default to floating. More control over moisture and sound, fewer things that can go wrong.
Sound Ratings: IIC and STC
The underlayment packaging displays both IIC ratings and STC ratings according to its contents. The technical terms will become clear when you understand that the numbers measure the floor’s ability to block sound.
- IIC (Impact Insulation Class): Footstep noise travelling downward. Walking, dropped objects, and impact sounds.
- STC (Sound Transmission Class): Airborne sound through the floor. Voices, music, TV.
| Home Type | Target Rating |
|---|---|
| Standard home | 50+ for both |
| Condos and apartments | 65+ IIC |
In a condo where downstairs neighbours are a real consideration, that IIC number matters more than anything else on the label.
Room-by-Room Guide
| Room | Underlayment | Why |
|---|---|---|
| Basement | Combination (foam + vapor barrier) | Moisture control |
| Bedroom | Foam or cork | Quiet and comfortable |
| Living room | Foam or combination | Comfort + durability |
| Kitchen | Combination | Moisture + durability |
| Condo / upper floor | Cork or rubber | Sound reduction |
| Home gym | Rubber | Maximum durability |
| Bathroom | Combination with a vapor barrier | Moisture protection |
Mistakes That Come Up Constantly
Many people make small mistakes during installation that later lead to damage. Avoid these 5 things:
- Double Padding: Built-in pad already there, extra underlayment added on top. Instability, joint failure, voided warranty. All three, usually.
- Carpet padding: Too soft, too thick, the floor feels spongy. Locking joints take constant stress, which they weren’t built for.
- Skipping subfloor prep: Underlayment doesn’t fix a bad subfloor. Dips and high spots get addressed before anything else goes down.
- Above 3mm: Joints loosen. Gaps form. Warranty gone.
- Not reading the manufacturer specs: Every brand has specific requirements. Some void warranties for unapproved products. Takes five minutes to check. Worth it.
What We Recommend
Foam works best for upper floors and standard living spaces with no moisture risk, making it the most affordable option. Cork is ideal where sound reduction matters, such as condos, multi-level homes, and bedrooms over living areas. Rubber is best for high-traffic areas, home gyms, and spaces with heavy furniture. Combination underlayment is the most versatile choice for concrete, basements, kitchens, and bathrooms where moisture protection is needed. When in doubt, a combination covers the most ground, and very few people come back wishing they’d chosen something else.
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Not Sure Which Underlayment You Need?
Our experts handle underlayment selection, subfloor repair, and full LVP installation across Bellevue and Redmond.
FAQs
Do I need underlayment if my LVP already has padding?
No extra underlayment is needed. Adding another layer on top of built-in padding creates instability and voids most warranties. The only exception concrete subfloor still needs a thin vapour barrier, even with the padding attached.
What happens if the underlayment is too thick?
Above 3mm, locking joints take stress they weren’t designed for. Gaps open between planks, squeaking starts, warranty gone. More thickness is not more protection here.
My LVP is waterproof. Do I still need a vapour barrier?
Yes. Waterproof LVP handles water from above. A vapour barrier handles moisture coming up from below through the concrete. Two different directions, two different problems. Skip the barrier over concrete, and you’re creating mould conditions under the floor.
What’s the best underlayment for LVP over concrete?
Combination underlayment foam or cork with a vapour barrier already built in. Moisture protection and cushioning are handled in one product.
Cork or foam, which is better for sound?
Cork, clearly. Denser material absorbs more sound. In a condo or multi-level home where noise between floors actually affects daily life, cork is worth the extra cost.
Best underlayment for vinyl flooring in apartments?
Cork or rubber. Both outperform basic foam for sound insulation by a real margin. Cork is the more common call for upper-floor apartments. Rubber makes more sense if you’re dealing with heavy furniture or gym equipment.
