- The maker's install guide decides. The wrong underlay can void a warranty.
- If the plank has a pad attached, usually don't add another (except a vapour barrier on concrete, if required).
- On concrete, you almost always need a vapour barrier.
- In condos, the underlay often decides whether the floor meets strata sound rules.
Underlay is the cheapest part of a floor job and one of the easiest to get wrong. Here's what it does.
What underlay does
- Sound: cuts the hollow "click-clack" and the noise that travels to rooms below.
- Moisture: a vapour barrier stops slab moisture coming up into the floor.
- Smoothing: covers tiny imperfections. It does not fix dips or humps. That's levelling.
- Comfort and warmth: a little.
The common types
| Type | Good for | Watch out |
|---|---|---|
| Basic foam | Budget laminate on wood subfloors | Little sound benefit |
| Foam with film (2-in-1) | Laminate or engineered on concrete | Tape the seams |
| IXPE (often pre-attached) | Vinyl and laminate, quiet and moisture-resistant | Don't double up |
| Cork | Sound and warmth; some vinyl comes with cork attached | Price |
| Felt / fibre | Engineered hardwood, sound | Needs a separate vapour barrier on concrete |
| Rubber / acoustic | Condos with strict IIC rules | Must match the maker's thickness limits |
| 6-mil poly | Vapour barrier on concrete | Not a cushion |
The mistakes we see
- Thick soft underlay under click vinyl. It lets the joints flex and break. Rigid vinyl needs a thin, firm base.
- Doubling up on a plank that already has a pad.
- No vapour barrier on a slab.
- Using underlay to "fix" an uneven floor. It doesn't.
Condos and strata
Many bylaws set a minimum IIC (impact sound) rating for the whole floor assembly. The rating depends on the floor plus the underlay plus the slab, so get the bylaw and the product's tested assembly data before ordering. More on condo flooring.
Common questions
Do you need underlay for vinyl plank with attached pad?
Usually not. Adding a second pad can let the joints flex and may void the warranty. On concrete, many makers still require a 6-mil poly vapour barrier underneath. Follow the install guide.
What underlay is best for laminate?
On wood subfloors, a quality foam or IXPE underlay. On concrete, one with a built-in vapour barrier or a separate 6-mil poly. For sound, look for acoustic underlays approved by the laminate maker.
Can underlay level an uneven floor?
No. Underlay only covers very small imperfections. Dips and humps must be levelled before installing a floating floor.
What underlay do condos need?
It depends on your strata bylaws, which often set a minimum IIC sound rating for the floor assembly. Use an acoustic underlay approved by the flooring maker that meets that rating.
Who's writing this: Rose and Thorn Flooring is a flooring company in Surrey, BC. We install floors for a living, so yes, we'd love to do yours. But nobody pays us to say nice things about a product, and we don't earn commission from any brand. If something here is wrong or out of date, text us at 604-716-4160 and we'll fix it.