Choosing and Fitting the Right Underlay for Laminate Flooring

Underlay is the layer most people forget about when they buy laminate, yet it affects how the floor feels, sounds and lasts. The right underlay depends mainly on your subfloor, whether that is concrete, timber or a floor with underfloor heating. Pick the wrong one and you can end up with a noisy, bouncy or damp-prone floor, and sometimes a voided warranty.

This guide covers how to choose underlay, how thick it should be, how to fit it and which mistakes to avoid. At Fife Premier Handyman Services, we fit laminate flooring across Fife, so this advice comes from the floors we lay in real homes. If you are still deciding between floor types, our laminate vs vinyl flooring guide will help you choose first.

Fife Premier Handyman Services covers flooring and other home improvement jobs, so see our handyman services in Fife if you need a hand.

What Underlay Does

Underlay sits between the subfloor and the laminate, and it does several jobs at once.

• Supports the click joints by giving the boards a stable, slightly forgiving base
• Evens out small imperfections in the subfloor, within limits
• Reduces noise, both the hollow sound of footsteps in the room and impact noise passing to rooms below
• Adds a little warmth and comfort underfoot
• Protects against moisture when the underlay includes a damp proof layer
• Helps the floor last by reducing stress on the boards and locking system

Laminate is a floating floor, so it is not fixed to the subfloor. That makes the underlay an important part of how the whole floor behaves.

Types of Underlay

There are several common types, each suited to different situations.

Standard Foam

This is the entry level choice, usually thin polyethylene foam. It suits flat, dry subfloors and offers modest comfort and sound reduction. It is a sensible option in a dry room with a good subfloor, but it will not cope with damp.

Foam With a Damp Proof Membrane

Many foam underlays come with a built-in film layer, often with an adhesive strip for sealing joins. This is the usual choice over concrete, where moisture can rise through the floor.

Fibreboard

Fibreboard underlay is made from compressed wood fibre. It is firmer than foam, which helps with minor imperfections, and it offers good insulation and sound absorption. It must be kept dry, so it is better suited to timber floors or concrete floors with a separate damp proof layer.

Rubber and Acoustic Underlay

Rubber based underlays are designed to reduce sound, particularly impact noise travelling to rooms below. They are popular in flats, where lease conditions often set limits on noise.

How Thick Should Underlay Be?

For most laminate floors, underlay of around 2mm to 3mm is a good starting point. Some products go up to about 5mm, but thicker is not automatically better.

• Too thin gives little comfort or sound reduction and does not help with small subfloor bumps
• Too thick or too soft lets the floor flex, which puts strain on the click joints and can lead to gaps, creaking and joint failure
• The manufacturer sets the limit. Most laminate brands specify a maximum thickness and a minimum compressive strength, so check before buying

Firmer underlay generally suits laminate better than soft, spongy foam, because the locking system needs a stable base.

Choosing by Subfloor

The subfloor is the most important factor in your choice.

Concrete Subfloors

Concrete can hold moisture, even when it looks and feels dry. That moisture can rise into the underlay and the laminate, causing swelling, mould and musty smells.

• Use a damp proof membrane. This can be built into the underlay, or a separate polythene sheet laid first, commonly a heavy gauge such as 1000 gauge
• Overlap and tape the joints so the barrier is continuous
• Turn the membrane up at the edges so it sits behind the skirting or trim
• Check the concrete is fully dry, particularly on new screeds, which need time to cure. A moisture test is the reliable way to confirm this
• Check flatness, because concrete floors are often uneven

Timber Subfloors

Timber floors, such as floorboards or sheet material over joists, behave differently.

• Avoid plastic damp proof layers, because they can trap moisture and cause rot in the timber, especially where there is a ventilated void below
• Choose a breathable underlay, typically foam without a vapour barrier or fibreboard, and check the manufacturer’s advice
• Fix loose boards and deal with squeaks before laying
• Check for damp, rot and woodworm in the timber, and sort these out first
• Level high or uneven boards, or lay a suitable sheet overlay such as ply or hardboard if needed
• Keep underfloor ventilation clear, so air can circulate beneath the floor

Underfloor Heating

Laminate can be laid over underfloor heating, but the underlay choice is critical.

• Use an underlay approved for underfloor heating. Standard thick foam can trap heat and reduce efficiency
• Check the thermal resistance, often shown as a tog value. Manufacturers commonly advise that the combined resistance of the underlay and the floor stays low, around 1.5 tog or below, but follow the product guidance
• Check the maximum floor surface temperature, which is typically around 27 degrees Celsius for laminate, though this varies
• Bring the heating up gradually after installation, as sudden temperature changes can stress the floor
• Keep the heating off or low while laying, and follow the manufacturer’s instructions for commissioning

Where the subfloor is concrete with heating pipes, a damp proof layer is still usually needed, so choose an underlay that provides both damp protection and low thermal resistance.

Noise and Acoustic Underlay

Laminate can sound hollow or clicky underfoot, and impact noise can travel to rooms below. A good underlay helps with both.

• Look for acoustic ratings, which often show the reduction in impact sound in decibels
• Check your lease if you live in a flat, because many leases require a minimum sound rating for hard flooring
• Consider rubber or dense fibreboard for the best sound reduction
• Remember the whole floor matters, because gaps at edges and hard contact with walls can carry sound too

If noise is a concern, it is worth spending a little more on a quality acoustic underlay.

Check the Manufacturer’s Requirements

This step is often skipped, and it can be costly.

• Many laminate warranties specify the type of underlay or set limits on thickness and compressive strength
• Some laminates come with underlay already attached. In that case, do not add a second layer unless the manufacturer says so
• Instructions often set subfloor conditions, such as flatness and moisture levels
• Keep the receipts and packaging information, in case you need to make a claim

Using the wrong underlay can void the warranty, so a few minutes reading the instructions is time well spent.

Preparing the Subfloor

Underlay is not a cure for a poor subfloor. Prepare the surface properly before anything goes down.

• Make it clean. Remove dust, debris, old adhesive and anything that could create bumps
• Make it dry. Check moisture levels, particularly on concrete and in rooms prone to damp
• Make it flat. Many manufacturers require no more than around 3mm of deviation over a 2 metre span, but check the specific requirement
• Make it firm. Fix loose boards and repair damaged areas
• Check doors and thresholds. The new floor and underlay add height, so doors may need trimming
• Let the laminate acclimatise. Most manufacturers advise leaving unopened packs in the room for a set period before fitting

How to Fit Underlay

Here is a general fitting sequence. Always follow the manufacturer’s instructions for your specific products.

1. Prepare the subfloor, making sure it is clean, dry, flat and firm
2. Lay the damp proof membrane if needed, over concrete, overlapping the joins and taping them
3. Start at one wall and roll out the underlay, cutting it to fit
4. Butt the joins together rather than overlapping, unless the manufacturer says otherwise, and tape them to stop movement
5. Keep the underlay flat with no folds, creases or bumps
6. Run it slightly up the walls, and trim it later once the skirting or trim is ready
7. Lay the laminate following the manufacturer’s pattern, leaving the required expansion gap at the edges, commonly around 10mm
8. Trim and finish with skirting, beading and door bars once the floor is complete

A tidy underlay installation makes laying the laminate much easier, and mistakes are far harder to correct later.

Common Mistakes to Avoid

• Doubling up underlay, which makes the floor too soft and can break the click joints
• Choosing the wrong thickness, whether too thin to be useful or too thick for the locking system
• Skipping the damp proof layer on concrete, which can lead to moisture damage
• Using plastic damp proofing on timber floors, which can trap moisture
• Ignoring underfloor heating requirements, and using standard thick foam
• Laying over an uneven subfloor, which causes gaps, creaking and joint failure
• Overlapping the underlay joins, which creates ridges under the boards
• Forgetting the expansion gap, so the floor has no room to move
• Using carpet underlay, which is too soft for laminate
• Ignoring the manufacturer’s instructions, and risking the warranty

Illustrative Scenarios

These examples show how the advice plays out in typical homes.

A ground floor concrete living room. The owner picks a foam underlay with a built-in damp proof membrane, taped at the joins and turned up at the edges. The concrete is checked for dryness first, so moisture is not trapped under the floor.

A first floor timber bedroom. The subfloor is an old floorboard surface. The fitter fixes loose boards, checks for damp, and uses a breathable fibreboard underlay without a plastic membrane, so the timber can still breathe.

A flat with underfloor heating. The owner needs both low thermal resistance and good sound reduction for the neighbours below. A thin, approved underfloor heating underlay with an acoustic rating suits both needs, and the lease conditions are checked before buying.

Fitting in Fife

Good underlay and careful fitting make a real difference to how a laminate floor looks and lasts. Fife Premier Handyman Services fits laminate flooring across Fife, including subfloor preparation, underlay, trims and finishing around doors and skirting. We give free, no obligation quotes, and we are happy to advise on the right underlay for your subfloor before any work begins.

Frequently Asked Questions

Do I need underlay for laminate flooring?

Yes, in almost all cases. Laminate is a floating floor, and underlay supports the click joints, reduces noise and adds comfort. Some laminates come with underlay attached, in which case you do not need to add more.

What is the best underlay for laminate on concrete?

An underlay with a built-in damp proof membrane, or a separate damp proof sheet beneath a standard underlay, is the usual choice. The joins should be overlapped and taped, and the concrete should be checked for dryness first.

What underlay should I use on a timber floor?

Choose a breathable underlay, such as foam without a vapour barrier or fibreboard, and avoid plastic damp proof layers that can trap moisture. Check the manufacturer’s advice and make sure the subfloor is flat and ventilated.

How thick should laminate underlay be?

Most laminate floors suit underlay of around 2mm to 3mm. Check the manufacturer’s limits, because underlay that is too thick or too soft can strain the click joints and cause gaps.

Can I use laminate underlay with underfloor heating?

Yes, if it is approved for underfloor heating and has a low thermal resistance. Check the maximum combined tog rating and floor temperature in the manufacturer’s guidance, and bring the heating up gradually.

Can I put two layers of underlay down?

No. Doubling up makes the floor too soft and can damage the locking system. Use one layer of the right type and thickness.

Does underlay really reduce noise?

Yes. A quality underlay reduces both the hollow sound inside the room and impact noise passing to rooms below. Acoustic and rubber based types perform best, which matters in flats and upstairs rooms.

Can I use carpet underlay under laminate?

It is not recommended. Carpet underlay is too soft and compressible for laminate, and it can cause the joints to flex and fail over time.

Final Thoughts

The right underlay for laminate flooring depends on your subfloor, your floor’s requirements and how you want the room to feel and sound. Protect concrete from damp, let timber breathe, choose a low resistance underlay for underfloor heating and keep to a sensible thickness. Prepare the subfloor properly, follow the manufacturer’s instructions and avoid the common shortcuts. Get the foundations right, and your laminate floor will feel better, sound better and last longer.