Does Hardwood Flooring Need Underlayment? It Depends on How It's Installed

"Does hardwood need underlayment?" is one of the most common questions we get, and the honest answer is that it depends on how the floor is installed. Putting the wrong thing under a hardwood floor can cause as many problems as leaving the right thing out.

We're Vision Flooring in Everett, WA. We install hardwood every way it can be installed: nail-down, staple-down, glue-assist, glue-down and floating. Here's what goes underneath each one, and why.

Does hardwood flooring need underlayment?

Every hardwood floor needs something underneath, but not always a cushioned pad. Nail-down hardwood goes over a vapor-retarder paper. Floating hardwood always needs a pad. Glue-down hardwood bonds straight to the subfloor with no pad at all. The right layer depends on the installation method, the subfloor and the flooring manufacturer's instructions.

What's the difference between underlayment and a subfloor?

The subfloor is the structure. Underlayment is a thin layer on top of it. The subfloor is the plywood, OSB or concrete that holds you up. Underlayment sits between the subfloor and the flooring to manage moisture, sound or movement. It can't make up for a subfloor that's uneven, damaged or wet. Those problems have to be fixed first, as we explain in how to prep a subfloor like a pro.

What goes under nail-down hardwood?

A vapor-retarder paper, not a foam pad. Nail-down hardwood, solid or engineered, is fastened through a layer of building paper into the plywood subfloor. The paper slows moisture moving up from below and reduces wood-on-wood squeaks. It's included in our nail-down installation price, along with the nails.

A soft foam pad doesn't belong under nail-down hardwood. It lets the boards flex between nails, which leads to squeaks and loose boards. In homes with special sound requirements, use only underlayments that the flooring manufacturer approves for nail-down installation.

Does floating engineered hardwood need a pad?

Yes, always. A floating floor isn't nailed or glued to the subfloor. It rests on a pad that cushions it, quiets footsteps and lets it expand and contract. Over concrete, a moisture barrier (commonly 6-mil polyethylene) goes down too, unless the pad has one built in.

We install two kinds of floating engineered hardwood. Tongue-and-groove floors with glued joints run about $2.50 per sq ft, and locking-system floors about $2 per sq ft. Both prices include installing the pad. The pad material itself is priced separately, and it has to be compatible with your flooring.

Does glue-down hardwood need underlayment?

Usually not. Glue-down hardwood bonds directly to the subfloor, typically concrete or another hard surface where nails can't be used. Some adhesives include built-in moisture control, and a few systems use a special sound mat in condos. Those are part of a manufacturer-approved system, not a separate pad. Our glue-down installation runs about $8 per sq ft, including the adhesive.

Wide-plank floors over plywood are often installed with glue-assist, which uses glue plus nails, at about $6 per sq ft.

Do condos need a special underlayment for hardwood?

Often, yes. Many condo associations require a sound-rated underlayment so footsteps don't carry to the unit below. These ratings are usually listed as IIC (impact noise) and STC (airborne noise). Ask your association for its written requirements before choosing flooring, because the underlayment has to meet those ratings and be approved by the flooring manufacturer for your installation method. We'll install to the spec.

What are the main types of hardwood underlayment?

Building paper for nail-down floors, foam or combination pads for floating floors, and cork or rubber when sound control matters most.

Can underlayment fix an uneven subfloor?

No. A pad follows the shape of whatever is under it. Dips and humps still show through, and a floating floor will flex over them, which can break its joints. Uneven subfloors need to be sanded, patched or leveled before the underlayment goes down.

Can hardwood go over radiant floor heating?

Many engineered hardwood floors can, but follow the manufacturer's radiant-heat instructions exactly. Thick or insulating pads slow down the heat getting to the room, so manufacturers limit what can go underneath. They also set rules for surface temperature and how fast the heat is turned up. Solid hardwood is a riskier choice over radiant heat.

Does LVP or laminate need underlayment?

Laminate always needs a pad. LVP needs one only if the product calls for it. If your LVP or laminate already has a pad attached, it goes straight onto the prepared subfloor, and we don't add a second pad. A second layer can make the floor too soft and strain the locking joints. See our LVP and laminate installation page for more.

How much does underlayment cost?

It depends on the product, so pad material is priced separately once you've chosen one. You can supply your own pad, or we can supply it, and if we do, we'll tell you the material cost and agree on it before we buy anything. Installing a pad is already included in our floating-floor prices. Vapor-retarder paper is included in our nail-down hardwood price.