Flooring Underlayment: What It Does and When You Can Skip It
2 min read · Last reviewed March 2026
Underlayment is the layer nobody sees and the one most likely to cause a callback if it is skipped or mismatched.
Underlayment sits between the subfloor and the finished flooring and does up to three separate jobs: moisture protection, sound dampening, and minor levelling. Not every flooring type needs all three, and using the wrong underlayment causes problems that show up months later, not on installation day.
The three jobs, separated
| Job | Why it matters | Typical material |
|---|---|---|
| Moisture barrier | Stops slab or subfloor moisture reaching the flooring from below | Plastic film, foam with vapour barrier |
| Sound dampening | Reduces impact noise, often required by building rules in apartments | Rubber, cork, dense foam |
| Minor levelling | Bridges tiny subfloor imperfections | Standard foam underlayment |
By flooring type
- Laminate: almost always needs underlayment unless it is a pre-attached-pad product; provides both sound dampening and slight cushioning.
- Engineered wood floating floor: same as laminate; glued-down installations instead need a moisture-blocking adhesive rather than a separate sheet.
- Vinyl plank (LVP): rigid-core products often include an attached pad already; adding a second layer can void the warranty by making the click-lock joints flex too much.
- Solid hardwood nailed to a wood subfloor: typically uses rosin paper, not foam, mainly to reduce squeaks rather than for cushioning.
- Tile: uses an uncoupling or crack-isolation membrane, not foam, since tile needs a rigid substrate, not cushioning.
When it is genuinely fine to skip it
Rigid-core vinyl plank with a factory-attached pad, installed over a dry, flat subfloor, generally does not need a separate underlayment, and the manufacturer's installation guide should be followed exactly since adding one can breach warranty terms.
Can I use the same underlayment everywhere in a house?
Only if every room has the same subfloor type and moisture exposure. A basement slab and an upstairs plywood subfloor almost always need different products.
Does thicker underlayment mean better performance?
Not necessarily. Beyond the manufacturer's recommended thickness, extra cushioning can make click-lock flooring joints flex and eventually fail.
Run the numbers for your own project
- Flooring CalculatorHow many boxes of flooring should I buy?
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