Do You Need Underlayment for LVP or Laminate? What to Use and Why

Underlayment is the layer between the subfloor and a floating floor. It can cushion, quiet footsteps, smooth tiny imperfections and block moisture from below. It also causes a lot of failed floors when the wrong kind goes under the wrong plank. Here is how to get it right for both LVP and laminate.

Do you need underlayment for LVP?

Often, no. Most click-lock rigid core LVP (SPC or WPC) comes with a pad bonded to the bottom, usually IXPE foam or cork. That pad is the underlayment, and the plank was tested with it. Adding another soft layer under it makes the floor bounce and puts stress on the click joints.

You may still need something under LVP when:

• The plank has no attached pad. Many manufacturers then allow a thin, dense underlayment made for rigid core LVP.
• You are over concrete. Many products call for a 6 mil poly vapor barrier over a slab, even with an attached pad. Some pads include a film that counts as the barrier. Check.
• You are in a condo or upstairs unit that requires a specific sound rating.

Glue-down LVP does not get an underlayment at all. It is glued to a smooth, flat subfloor.

Do you need underlayment for laminate?

Yes, in almost every case. Laminate has a hard HDF core and needs a pad to cushion it, quiet it and keep it from clicking against the subfloor. Some laminate comes with a pad attached. If not, you add one. Over concrete, laminate also needs a vapor barrier because its wood-fiber core will absorb moisture from the slab and swell. The usual approach is 6 mil polyethylene sheeting under the pad, or a combination underlayment with a film already bonded to it.

Types of underlayment

Why thick soft underlayment breaks rigid core LVP

This is the mistake we see most. People assume thicker and softer feels nicer, so they buy a plush 3 mm foam. Under rigid core LVP, that foam compresses every time someone steps near a joint. The click locks flex up and down thousands of times, then crack, gap or peak. Many manufacturers limit underlayment under rigid core LVP to something thin and dense, often in the range of 1 to 1.5 mm, and some forbid any extra layer when there is an attached pad. Check the exact limit in your instructions. Firm is the goal, not plush.

Sound control: IIC and STC in condos

If you live in a condo or apartment, check the association rules before you buy anything. Many require a minimum sound rating for the floor assembly.

• IIC (Impact Insulation Class) measures impact noise, like footsteps and dropped objects, heard in the unit below.
• STC (Sound Transmission Class) measures airborne noise, like voices and TV.

Higher is better for both. Building codes for multifamily construction commonly use 50 as a baseline, and many associations ask for more. Ratings depend on the whole assembly (plank, underlayment, subfloor and ceiling below), so ask the manufacturer for test data that matches your setup and get the association's approval in writing.

Do you need underlayment over a plywood or OSB subfloor?

For laminate, yes. A pad is still needed for cushion and sound, but a separate vapor barrier usually is not required over a wood subfloor above a conditioned space. Some manufacturers want a barrier over wood when the floor is above a crawlspace or unheated area, so read the instructions. For LVP with an attached pad, a plywood or OSB subfloor usually needs nothing else, as long as it is flat, dry and screwed down tight.

Underlayment over radiant floor heat

Radiant heat changes the rules a bit. Thick or highly insulating underlayment slows heat getting into the room, so manufacturers often specify thin products or list a maximum thermal resistance. Most also set a maximum floor surface temperature for the planks, and some do not allow certain products over radiant at all. Check that the plank, the underlayment and the heating system are all approved together before you buy.

Going over an existing floor

If you are floating over old vinyl or tile, the old floor is usually treated as the subfloor. A plank with an attached pad often goes right over it. Never float over carpet. See can LVP go over an existing floor.

What you'll need

• The correct underlayment for your plank and subfloor
• 6 mil poly sheeting, if a separate vapor barrier is required over concrete
• Underlayment or moisture barrier tape
• Utility knife and straightedge
• Broom and shop vac
• Level or straightedge (6 to 10 ft) to check flatness
• Moisture test supplies or meter for concrete

How to install underlayment

1. Read the plank's install instructions first. They list allowed underlayments, maximum thickness, whether a vapor barrier is required, and what voids the warranty.
2. Check flatness. Most floating floors call for about 3/16" in 10 ft (some 1/8" in 6 ft). Underlayment does not fix dips or humps. Grind highs and fill lows first. See subfloor leveling.
3. Clean thoroughly. Sweep and vacuum. A single screw head or chunk of drywall mud will show up as a bump through the plank.
4. On concrete, test for moisture. Follow the product's required test (calcium chloride or in-situ RH). More in LVP in basements.
5. Lay the vapor barrier if required. Roll out 6 mil poly with seams overlapped (commonly 6 to 8 inches) and taped, running a few inches up the wall to be trimmed later.
6. Roll out underlayment one row at a time. Butt the seams, do not overlap them unless the instructions say to, and tape them. Overlapped foam creates a ridge.
7. Install planks as you go. Lay a few rows of underlayment ahead of the floor so you are not walking on it all day.

What voids an LVP or laminate warranty?

• Adding a second pad under a plank with an attached pad
• Using an underlayment thicker or softer than allowed
• Skipping a required vapor barrier over concrete
• Installing over a subfloor that is out of flat or over moisture limits
• Laying a floating floor over carpet or carpet pad
• Pinning a floating floor under cabinets or a kitchen island

Common mistakes to avoid

• Buying the thickest, softest pad in the store for rigid core LVP.
• Using an underlayment to hide an uneven subfloor.
• Forgetting the vapor barrier under laminate in a basement.
• Doubling up a separate poly sheet with an underlayment that already has a film, when the instructions say not to. It can trap moisture in odd places.
• Not taping seams, so the pad shifts and bunches as planks go down.

When to hire a pro

Call an installer if the slab shows signs of moisture, the subfloor needs leveling, or a condo association requires documented sound ratings. In homes built before 1978, old resilient flooring and adhesive can contain asbestos and old painted trim can contain lead, so test before tearing out or have a certified pro handle it. For the full install, see how to install LVP and how to install laminate.

Need it done for you?

We install LVP and laminate with the underlayment the manufacturer calls for. Book a free in-home estimate and you get a written fixed-price quote within 48 hours.