Do you need underlay beneath laminate?

Yes. Laminate is a floating floor and needs an underlay, unless the boards have one already attached. Underlay supports the locking joints, evens out very minor imperfections and reduces noise. Over concrete, a moisture barrier is normally needed as well. The right type depends on your subfloor, the room below and any underfloor heating.

Underlay isn’t an optional extra with laminate. It’s part of how a floating floor is designed to work, and the wrong one can cause as many problems as none at all.

What does laminate underlay do?

• Supports the joints. Laminate is clicked together and sits on the underlay rather than being fixed down. A suitable underlay gives the boards even support so the joints aren’t stressed as you walk on them.
• Evens out very minor imperfections. It can take up small irregularities, but it won’t fix an uneven floor. Dips and ridges still need dealing with first.
• Reduces noise. Underlay can cut the hollow “clicky” sound of footsteps in the room and reduce impact noise to rooms below.
• Protects against moisture. Over concrete or screed, a vapour barrier stops residual moisture rising into the boards.
• Adds a little comfort and warmth underfoot.

Which underlay do you need over concrete?

Concrete and screed floors can release moisture for years, especially in newer homes. Laminate manufacturers generally require a moisture barrier over these floors. That can be an underlay with an integrated vapour barrier, or a separate polythene damp-proof membrane laid with overlapped and taped joints and turned up at the walls, under the underlay.

Some laminate underlays state an SD value, which measures resistance to water vapour; manufacturers often look for a high figure (75 m or more is a commonly quoted benchmark) over concrete. A moisture barrier manages normal residual damp; it doesn’t fix a floor that is actually wet, which needs investigating first. See when to install flooring in a new-build for more on drying times.

Which underlay do you need over floorboards?

Over a sound, flat timber floor, a standard laminate underlay is usually suitable. Fibreboard underlays are sometimes used over boards because they help smooth out small gaps and add some insulation, but they aren’t compatible with every laminate or with underfloor heating, so check first.

A plastic damp-proof membrane isn’t normally recommended over suspended timber floors, as it can trap moisture in the timber, but follow the laminate manufacturer’s guidance. The boards themselves must be secure and flat; see laminate over floorboards.

Laminate with underlay already attached

Many laminates now come with a thin underlay bonded to the back of each board. In that case, adding another underlay on top is usually not allowed, because the extra cushioning can stress the joints. Over concrete, a separate moisture barrier is often still needed underneath. The product instructions say exactly what is permitted.

Underlay for flats and upstairs rooms

If you live in a flat, your lease or management company may set a minimum sound-reduction standard for hard flooring. Acoustic underlays are designed for this and quote an impact sound reduction figure in decibels. Check the lease before choosing a floor, because the requirement can apply to the whole floor build-up rather than just the underlay.

Underlay with underfloor heating

Underlay slows heat getting through to the room. For underfloor heating, choose an underlay the laminate and heating manufacturers approve, with a low thermal resistance or tog rating. Guidance often suggests keeping the combined resistance of floor and underlay to around 0.15 m²K/W (1.5 tog) or less, but check the specific products.

Is thicker underlay better for laminate?

Not necessarily. A soft or very thick underlay lets the boards flex at the joints, which can lead to gaps, creaking or broken locking edges. Laminate underlays are usually only a few millimetres thick for this reason, and manufacturers often specify the type and thickness. Never use carpet underlay under laminate; it is far too soft.

Board thickness is a separate question; see 8mm vs 12mm laminate.

Common questions

Can you lay laminate without underlay?

Only if the boards have an underlay already attached, and even then a moisture barrier may be needed over concrete. Laying laminate straight onto a subfloor without either is likely to be noisy, uncomfortable and outside the manufacturer’s instructions.

Can I reuse old underlay?

It isn’t usually worth it. Old underlay is often compressed, damaged or the wrong type for a new floor, and it’s a small part of the overall cost.

Is laminate underlay the same as LVT underlay?

Not always. Many click LVT products require a specific, firmer underlay or have one attached. See LVT subfloor preparation.

Next step

When you ask for a laminate estimate, let us know what the floor is made of if you can, or request a home measure so the right underlay for your subfloor can be confirmed. With supply and fit, the underlay is chosen alongside the flooring. See also the underlay definition.