What Goes Under LVP Flooring: Pros, Cons, and Buying Guide

If you are asking what goes under LVP flooring, you are already ahead of most DIYers, because what is beneath the plank determines whether the floor feels solid and lasts or telegraphs every bump and lifts at the seams. The short answer is that it depends on your subfloor and the plank you bought, and getting it wrong is the leading cause of vinyl floors that fail. Many SPC and WPC planks come with underlayment already attached, in which case adding more can actually void the warranty. Let’s break down the layers so you order and install correctly.

The Subfloor Comes First

Before any underlayment conversation, the subfloor itself must be right. Luxury vinyl plank is thin and somewhat flexible, so it conforms to imperfections beneath it. A high spot creates a wear point; a low spot creates a hollow that flexes and eventually cracks the locking joints. The subfloor must be clean, dry, flat, and structurally sound.

• Flatness: Most manufacturers require no more than 3/16 inch of variation over 10 feet. Grind down high spots and fill low spots with a cementitious self-leveling compound.
• Cleanliness: Sweep and vacuum thoroughly; even small grit beneath the plank causes squeaks and wear.
• Dryness: A damp concrete slab will eventually cause problems even under waterproof vinyl by trapping moisture and breeding mold.

Over Concrete vs. Over Wood

The right approach depends entirely on what the subfloor is made of. Over a concrete slab, your biggest concern is moisture migrating up from the ground. Concrete wicks moisture even when it feels dry, so a vapor barrier or moisture-resistant underlayment is usually essential. Over a plywood or OSB subfloor, moisture is less of an issue, but flatness and any squeaks should be addressed first by screwing down loose sheets to the joists.

When You Need a Vapor Barrier

A vapor barrier is a thin plastic film, typically 6-mil polyethylene, that blocks moisture from passing up through a concrete slab into your floor. Over any below-grade or on-grade concrete, you almost always want one unless your plank’s attached pad already includes a moisture barrier. Run a simple moisture test first: tape a 2-by-2-foot square of plastic to the bare slab for 24 to 72 hours, and if condensation forms underneath, you have a moisture issue that must be controlled before installation.

Underlayment: When Yes, When No

This is the question that trips people up. Whether you add a separate underlayment pad depends on the plank.

• Planks with attached underlayment: Most quality SPC and WPC planks include a pre-attached IXPE or cork pad. Do not add a second pad; stacking underlayment creates too much cushion, the joints flex, and you can void the warranty.
• Planks without attached pad: A separate floating-floor underlayment adds sound dampening and minor cushioning. Choose one rated for vinyl, ideally with a built-in vapor barrier over concrete.
• Glue-down LVP: No underlayment at all; the plank bonds directly to a properly prepped subfloor with adhesive.

Always check your specific product’s installation guide. The manufacturer dictates what is allowed, and following it is what keeps the warranty intact.

Why Thicker Underlayment Is Not Better

It is tempting to think a plush, thick pad makes for a more comfortable floor. With LVP the opposite is true. Vinyl plank relies on a stable base; too much cushion lets the floor deflect under foot traffic and furniture, which stresses the click-lock joints until they separate or crack. For floating LVP that needs underlayment, look for a thin, firm, high-density pad in the 1mm to 1.5mm range designed specifically for rigid-core vinyl, not the thick foam sold for laminate.

Existing Flooring: Can LVP Go Over It?

One of LVP’s selling points is that it can often float over existing hard surfaces, saving demolition. You can usually install over old vinyl, tile, or hardwood as long as the surface is flat, well-bonded, and clean. Fill deep tile grout lines so they do not telegraph through. Never install LVP over carpet; the cushion causes the same deflection problems as thick underlayment. And if the existing floor is loose, damaged, or hiding moisture, remove it rather than burying a future problem.

The Mistakes That Ruin LVP Floors

Most vinyl plank failures trace back to a handful of avoidable errors beneath the surface.

1. Skipping the flatness check and installing over a wavy subfloor.
2. Stacking a separate pad under planks that already have one attached.
3. Using thick, soft laminate underlayment under rigid-core vinyl.
4. Ignoring slab moisture and skipping the vapor barrier.
5. Failing to leave the required expansion gap around the perimeter.

Fix the base and respect the manufacturer’s instructions, and LVP is one of the most forgiving and durable floors you can install.

A Quick Layer-by-Layer Recap

From the bottom up, a typical floating LVP installation over concrete looks like this: structurally sound, level slab; vapor barrier or moisture-resistant underlayment as required; the LVP plank itself, with attached pad if it has one; and finally the expansion gap concealed by baseboard or quarter-round. Over a wood subfloor, the layers are similar minus the heavy moisture concern. Keep it simple, keep it flat, and do not over-cushion.

How to Test and Prep a Concrete Slab

Because so many LVP failures start at the slab, it is worth knowing the prep sequence in detail.

1. Run the plastic-sheet moisture test, and if you suspect a problem, use a calcium chloride or relative humidity test for a quantified reading.
2. Grind down high spots and fill low spots with a cementitious self-leveling compound, then recheck flatness with a straightedge.
3. Clean the slab thoroughly so no grit, paint, or adhesive residue remains under the new floor.
4. Lay the vapor barrier or moisture-resistant underlayment per the manufacturer if your plank does not have an attached pad with a built-in barrier.
5. Acclimate the planks in the room for the manufacturer’s specified time before installing.

Underlayment for Sound Control

One legitimate reason to add underlayment, when the manufacturer allows it, is sound. In multi-story homes and condos, footstep noise transmitting to the room below is a real concern, and many HOAs require a minimum impact insulation rating. A thin, firm acoustic underlayment rated for rigid-core vinyl can improve sound performance without the deflection problems of soft foam. If you go this route, choose a product specifically engineered for LVP, confirm it does not exceed your plank’s allowed pad thickness, and check that combining it with any attached pad will not void the warranty. When in doubt, a glue-down installation over a quiet subfloor often beats stacking cushion.

Bottom Line

Knowing what goes under LVP flooring comes down to a clean, dry, flat subfloor, a vapor barrier over concrete, and the right underlayment, which often means no extra underlayment at all when your plank already has a pad attached. Test for moisture, level the base, follow your manufacturer’s guide to the letter, and resist the urge to add thick cushion. Get the foundation right and your luxury vinyl will feel solid and last for decades.