Flooring Underlayment Guide: What You Actually Need

Underlayment is one of those flooring purchases that's easy to get wrong — either buying too much, buying the wrong type, or buying product that duplicates what's already built into your flooring. This guide cuts through the confusion and tells you exactly what you need for each flooring type.

What Underlayment Does

Underlayment is a thin layer of material installed between your subfloor and your finished flooring. It serves multiple functions:

Sound dampening: Reduces impact noise (footsteps, dropped items) from transmitting through the floor to rooms below. The denser and thicker the underlayment, the better the sound reduction.

Moisture barrier: In concrete slab installations, underlayment with a vapor barrier prevents ground moisture from reaching wood-based flooring.

Subfloor imperfection tolerance: Some underlayment provides minor leveling over small bumps and dips — though it is not a substitute for proper subfloor preparation.

Thermal insulation: Adds a small amount of thermal resistance, reducing heat loss through the floor.

Comfort: Provides slight cushioning underfoot.

Does Your Flooring Need Underlayment?

LVP with Pre-Attached Underlayment

Many LVP products come with underlayment pre-attached to the back of the plank — typically a thin layer of foam or cork. If your LVP has this, you generally do not need additional underlayment.

Exception: When installing over concrete, even LVP with attached underlayment benefits from a separate vapor barrier film (6-mil polyethylene sheeting) if the attached underlayment doesn't include a vapor barrier.

Read your specific product's installation guide. Adding extra underlayment under LVP with pre-attached underlayment can:

• Make the floor feel spongy
• Cause the click-lock seams to experience excess stress
• Void the warranty

LVP Without Pre-Attached Underlayment

You'll need to add underlayment. Choose:

• Thin foam (1–2mm): Adequate for most floating LVP applications over wood subfloor
• Foam with vapor barrier: Required for concrete slab installations

Laminate Flooring

Laminate almost always requires underlayment. Unlike many LVP products, laminate rarely comes with pre-attached underlayment. Choose:

• Basic foam (2–3mm): Minimum for residential use
• Foam with vapor barrier: For concrete slab installations
• Cork or rubber: Better sound dampening; worth the upgrade if the floor is above a living space

Engineered Hardwood (Floating)

Floating engineered hardwood needs underlayment:

• Cork (3–6mm): Best choice for engineered hardwood — moisture-resistant, good sound dampening, compatible with engineered hardwood
• Foam with vapor barrier: For concrete subfloors

Do not use rubber underlayment under hardwood products — it can trap moisture.

Solid Hardwood (Nail-Down)

Solid hardwood is nailed or stapled directly to a wood subfloor. Traditional underlayment is not used. However, a layer of building paper (rosin paper) is often installed between the subfloor and hardwood to:

• Provide a slight moisture barrier
• Reduce squeaks
• Provide a smooth nailing surface

Tile (Ceramic/Porcelain)

Tile does not use foam underlayment. Tile requires a rigid, stable substrate:

• Cement backer board (e.g., Durock, Hardiebacker): Standard substrate for tile in wet areas and over wood subfloors
• Uncoupling membrane (e.g., Schluter Ditra): A better alternative over wood subfloors — prevents cracked tiles from subfloor movement
• Direct to concrete: Porcelain can be set directly to concrete if it's clean, flat, and structurally sound

Carpet

Carpet uses a pad (cushion) rather than traditional underlayment:

• 8 lb rebond pad: Standard residential carpet pad; good durability
• Memory foam pad: More comfortable but compresses faster under heavy furniture
• Rubber pad: For Berber and low-pile carpets; prevents carpet from stretching

Choosing Underlayment by Performance Need

Budget Application

Product: 2–3mm foam underlayment Price: $0.15 – $0.25/sq ft Best for: Laminate and LVP without attached underlayment in above-grade rooms over wood subfloor

Standard Residential

Product: 3mm foam with integrated vapor barrier Price: $0.20 – $0.40/sq ft Best for: LVP or laminate over concrete; adds moisture protection

Sound Dampening Priority

Product: Cork underlayment (3–6mm) or rubber composite Price: $0.40 – $0.80/sq ft Best for: Above-garage rooms, condos and apartments, homes with hard floors on upper levels where footstep noise transmits to living areas below

Premium

Product: Dense rubber and foam composite with vapor barrier Price: $0.60 – $1.20/sq ft Best for: Maximum sound dampening in multi-family or multi-story applications

Underlayment Thickness: More Is Not Always Better

For click-lock floating floors, underlayment that's too thick can cause problems:

• Click-lock seams flex more than designed, causing joint failure over time
• The "spongy" feel is uncomfortable and concerning to buyers
• Some manufacturers limit underlayment thickness to 3mm maximum

For LVP specifically, 1.5–3mm underlayment is typically appropriate. Thicker foam under LVP is not recommended.

Laminate handles slightly thicker underlayment (up to 4–5mm) better than LVP.

Vapor Barrier Requirements

For any flooring installed over concrete:

• A vapor barrier is required for wood-based flooring (engineered hardwood, laminate)
• A vapor barrier is strongly recommended for LVP (protects subfloor and reduces mold risk)
• Tile over concrete doesn't need a vapor barrier for the tile itself, but cement board seams should be waterproofed in wet areas

If your underlayment doesn't include an integrated vapor barrier (most foam underlayments now do), install 6-mil polyethylene sheeting under the underlayment, with seams overlapped 8 inches and sealed with vapor barrier tape.

Buying Underlayment at Liquidators

Underlayment often appears at flooring liquidators along with the flooring it was originally sold with. If a store has a significant stock of LVP, they may also have compatible underlayment at discount prices.

Check what's available before buying underlayment elsewhere — you may save 30–50% on underlayment at the same liquidator where you buy your flooring.