What you put under vinyl flooring matters as much as which planks you pick. The right base layer keeps the floor flat, blocks moisture coming up from a slab, softens the feel underfoot, and stops you from hearing every footstep echo through the room. Get it wrong and you’ll see telegraphing of subfloor bumps within months, hear hollow taps where planks aren’t supported, or — worst case — pull the floor up two years in because moisture has wrecked the underlay. Here’s how to think about each layer.
Start with the subfloor — the layer most people skip
Vinyl is thin and flexible. Anything under it shows through, eventually. The single biggest determiner of how a vinyl floor looks and lasts is whether the subfloor was properly prepared before the first plank went down.
- Flat, not just level. Manufacturers typically specify a tolerance of around 3 mm over 2 metres. A floor can be perfectly level overall but have local high and low spots that need patching with self-levelling compound.
- Clean. No paint flecks, plaster lumps, screws, or grit. Anything sharp will eventually press up through the wear layer.
- Dry. Concrete slabs less than 60 days old still hold construction moisture. New slabs need a moisture test before vinyl goes down.
- Structurally sound. Squeaky timber subfloors don’t get fixed by laying vinyl over them. Re-screw or pack any loose boards first.
For the slab side specifically, our notes on how to lay vinyl on a concrete floor cover the prep checklist and what to do if the slab is uneven.
Moisture barrier: when you need one, when you don’t
Moisture barriers are non-negotiable on concrete slabs, especially ground-floor slabs in Brisbane and Sydney where humidity is high year-round. A 200-micron polyethylene sheet between the slab and the underlay (or directly under the planks for some click-lock systems) blocks water vapour rising up from the concrete. Without one, vapour can pool under the floor, swell MDF-core products, and grow mould on the slab side of the underlay.
On a timber subfloor in a properly ventilated upper level, you usually don’t need a separate moisture barrier — the airflow underneath the joists handles it. Always check the manufacturer’s install spec, though. Some SPC hybrid products void warranty if a moisture barrier isn’t fitted on a slab.
Underlay — and when it’s already in the box
Underlay is the layer between the moisture barrier (or subfloor) and the vinyl planks. Its job is acoustic dampening, slight cushioning, and minor levelling of small subfloor imperfections. Whether you need a separate underlay depends on the product:
- Click-lock SPC hybrid with pre-attached IXPE pad: the underlay is already bonded to the back of each plank. Adding a second layer of foam underlay on top isn’t recommended — too much give underfoot causes the click joints to flex and eventually fail. We’ve covered this in detail in do you need underlay for vinyl flooring.
- Click-lock LVP without a pre-attached pad: needs a thin (1.5-2 mm) foam or IXPE underlay. Don’t go thicker — vinyl needs a firm base, unlike laminate which can sit on 3 mm foam.
- Glue-down LVP: bonds directly to the prepared subfloor. No underlay. The adhesive is the bond layer.
- Loose-lay vinyl: sits on the subfloor with friction-grip backing. Some products allow a thin underlay, most don’t. Check the spec sheet, and see our notes on the expansion gap on loose-lay vinyl while you’re at it.
Foam, IXPE, cork or rubber?
If you do need a separate underlay for click-lock vinyl, here’s how the common types compare:
- Foam (EVA or PE): the cheapest option. Fine for a small bedroom over a flat slab. Compresses faster than higher-density alternatives.
- IXPE (cross-linked polyethylene): denser and more resilient than basic foam. Better acoustic performance, longer service life. The default upgrade pick.
- Cork: good acoustic dampening and a slight thermal benefit. More expensive, and not the right pick over a slab without an integrated moisture barrier — cork can hold moisture.
- Rubber: the highest acoustic spec, used in apartments where impact-noise ratings are required by strata. Heavy, more expensive, and overkill for most family homes.
Acoustic upgrades for apartments and upper levels
Strata buildings often spec a minimum impact-insulation rating for any hard flooring on upper levels. If that’s you, the underlay is a compliance item, not a comfort one. A 3 mm rubber or dense IXPE acoustic underlay paired with a glue-down LVP is the standard solution. Get the body corporate’s flooring policy in writing before you order — replacing an underlay after install is expensive.
The short version
Prep the subfloor properly. Use a 200-micron poly moisture barrier on every slab. For click-lock SPC with pre-attached IXPE, no extra underlay. For bare click-lock LVP, a thin IXPE pad. For glue-down, no underlay. For apartments, check the strata acoustic spec before you buy. If you’re picking the vinyl product itself for a wet zone or pet household, our waterproof flooring options guide is the next read. Drop into our Sydney or Brisbane showroom if you want us to look at your subfloor photos before you commit.
Ready to shop? Browse our full vinyl plank flooring range online, or drop into our Sydney or Brisbane showroom to see the range in person.