Underlay
A layer of material installed beneath flooring to provide cushioning, sound insulation, thermal insulation, and moisture protection.
Underlay is the hidden layer of material that sits between your subfloor and the visible floor covering. Though you will never see it once the floor is laid, underlay plays a critical role in how your flooring looks, feels, and performs over time.
What underlay does
- Sound insulation — reduces impact noise (footsteps) and airborne sound travelling between floors. Essential in flats and apartments where noise transfer to neighbours is a concern.
- Thermal insulation — adds a layer of warmth, particularly important on ground floors and concrete subfloors
- Cushioning — makes the floor more comfortable underfoot and protects the flooring material from minor subfloor imperfections
- Moisture protection — a built-in or separate moisture barrier prevents damp from the subfloor reaching the flooring above
Types of underlay
Different flooring types require different underlay:
- Carpet underlay — typically foam, rubber, or felt. Thicker and softer for cushioning. Rubber underlays last longer and provide better support.
- Laminate and engineered wood underlay — thin foam or cork sheets, often with an integrated moisture barrier. Must be firm enough to support the click-lock joints.
- LVT underlay — some LVT products have underlay built in. If not, use a thin, firm underlay specifically designed for vinyl — standard carpet underlay is too soft and will cause the floor to flex.
When underlay is not needed
Glue-down flooring (both LVT and engineered wood) typically does not use underlay because the flooring is bonded directly to the subfloor. Always check the flooring manufacturer’s recommendations — using the wrong underlay (or no underlay when one is required) can void the product warranty.
Cost considerations
Underlay is often overlooked in renovation budgets, but it adds up across a whole property. It typically costs between 10-20% of the flooring cost itself. When comparing flooring quotations, check whether underlay is included or listed as a separate line item — this is a common area where quotes differ.