Acoustic Underlay for Wood Flooring: A Complete UK Guide

Acoustic underlay for wood flooring is a thin, resilient layer laid between a floating wood floor and the subfloor to cut impact noise, level minor surface flaws and add a little thermal insulation. It is normally 2–10 mm thick and is used under engineered wood, laminate and some solid boards. This guide explains how it works, which materials suit UK homes and what the Building Regulations expect.

• Approved Document E requires new-build separating floors in England and Wales to achieve at least 45 dB DnT,w + Ctr for airborne sound and no more than 62 dB LnT,w for impact sound, with conversions set at 43 dB.
• Acoustic underlay for floating wood floors is normally supplied between 2 mm and 10 mm thick, with 3–5 mm the most common range for engineered wood and laminate.
• Manufacturers of tested acoustic underlay systems commonly quote impact-noise improvements of 15–25 dB, measured in laboratory conditions rather than in occupied rooms.

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What is acoustic underlay for wood flooring?

Acoustic underlay for wood flooring is a resilient sheet or mat that sits between a floating wood floor and the subfloor, decoupling the two layers so impact noise and minor unevenness are absorbed rather than transmitted.

Wood flooring is hard, dense and thin compared with carpet, so footsteps, dropped objects and furniture legs pass almost straight through to the structure below. An acoustic underlay interrupts that path. It is a compressible layer — usually foam, rubber, cork or fibre — laid across the whole floor area before the boards go down.

It differs from a plain levelling underlay, which only fills small troughs in a screed or timber subfloor. Acoustic products are specified by dynamic stiffness and tested impact-sound performance, not just by thickness. A good underlay may also act as a vapour barrier or thermal break, depending on the material.

Underlay is generally used with floating floors: engineered wood, laminate and click-together boards. Solid timber that is nailed or fully glued down usually cannot take a soft layer, because the fixings must reach the subfloor for stability.

How does acoustic underlay reduce noise?

It reduces impact noise by absorbing the vibration created when something strikes the floor, and it can add a small amount of airborne sound insulation by sealing gaps and adding damping.

Impact noise — footsteps, chairs, washing machines — travels through the structure as vibration. A resilient underlay compresses slightly under load and converts part of that energy into heat, so less reaches the ceiling of the room below or the neighbouring flat.

Airborne noise, such as speech or a television, behaves differently. Underlay helps far less here, though a dense, well-sealed system with taped joints can contribute a decibel or two. Where airborne performance matters, underlay is normally combined with a floating screed or a separate acoustic ceiling.

Manufacturers commonly quote 15–25 dB of impact-noise improvement for tested systems, measured in laboratory conditions. Real installations often deliver less, because flanking paths through walls, joists and service openings bypass the underlay entirely. Treat the figure as a comparison tool rather than a guarantee.

Which underlay materials suit wood flooring?

Foam and rubber are the most common choices for wood flooring, while cork, wood fibre and felt offer better natural damping and are often preferred where underfloor heating or a more sustainable specification is involved.

Closed-cell polyethylene foam is inexpensive, light and easy to cut, and it works well under laminate. Crumb rubber is denser and heavier, so it performs better under impact and helps flatten minor undulations. Both are typically supplied in 3–5 mm sheets or rolls.

Cork is a natural option with good resilience and low thermal resistance, which makes it a favourite under engineered wood on underfloor heating. Wood fibre boards are firmer and add a little rigidity, while felt feels quiet underfoot but can compress over time in busy areas.

For flats, look for products with documented dynamic stiffness and a tested DnT,w figure rather than a marketing decibel claim. Many suppliers publish these values in technical data sheets, and a factor such as s' measured in MN/m³ is worth checking before you buy.

How thick should acoustic underlay be?

For most floating wood floors, 3–5 mm is the practical range; thicker does not automatically mean quieter, and soft layers above roughly 10 mm can let joints flex and fail.

Thickness matters less than density and stiffness. A 3 mm rubber mat will usually outperform a 10 mm soft foam, because it does not collapse under load and keeps the floor base stable across the whole room.

Too much give is a genuine problem. Click-lock joints rely on a firm base; if the underlay compresses at the edges, the locking profile can crack and the finished floor will creak. Follow the flooring manufacturer's maximum underlay thickness, which is usually stated in the installation guide.

Underfloor heating adds a further constraint. Aim for a combined tog rating below about 1.5 for the whole floor build-up, and choose cork, rubber or a dedicated thin acoustic product rather than a thick insulating foam that traps heat.

What do UK Building Regulations require?

Approved Document E of the Building Regulations sets minimum sound insulation standards for separating floors, and acoustic underlay is one of the tools used to meet them.

For new-build dwellings in England and Wales, separating floors must achieve at least 45 dB DnT,w + Ctr for airborne sound, with a maximum impact-sound level of 62 dB LnT,w. Conversions have a slightly lower airborne requirement of 43 dB.

Scotland and Northern Ireland publish separate guidance, though the underlying principles are similar. In every case the requirement applies to the complete floor construction, not to the underlay on its own. Underlay cannot rescue a floor that lacks mass or has unsealed service penetrations.

If you are converting a house into flats or adding an extension with a habitable room above, expect your building control body to ask for evidence — either a tested system specification or a post-completion sound test on site.

How should acoustic underlay be installed?

Install it over a clean, flat subfloor with joints tightly butted and taped, run it across the full floor area without gaps, and leave a small expansion gap at the perimeter.

Preparation matters more than the product. Sweep or vacuum the subfloor, check for high spots, and secure any loose boards or protruding nails. Where the base is concrete, lay a damp-proof membrane first unless the underlay itself is moisture-resistant.

Butt the underlay strips together and seal the joints with the tape recommended by the supplier; a gap lets sound and draughts pass straight through. Carry the layer right to the walls and trim it after the floor is down, keeping about a 10 mm expansion gap around the perimeter for the wood.

Do not overlap the underlay, and do not double it up hoping for better performance — stacked layers become unstable and voids form. Once the floor is laid, seal skirting, pipe collars and door thresholds to close the remaining noise paths.

What does acoustic underlay cost in the UK?

Expect to pay roughly £3 to £12 per square metre for acoustic underlay in the UK, depending on material, thickness and whether tested performance data is supplied.

Basic foam starts at around £2–£4 per m², crumb rubber and cork generally sit between £5 and £10 per m², and high-performance systems with full test certificates can exceed £12 per m². A typical 20 m² room therefore costs £60–£240 in underlay alone.

Factor in tape, a damp-proof membrane and any levelling compound, which together often add a third to the underlay budget. Buying larger rolls usually reduces the unit price, but only if the leftover material is genuinely usable on another room.

Cheap underlay can be a false economy in flats. If a sound test fails, lifting and relaying the floor costs far more than the price gap between unbranded foam and a certified acoustic product. Our blog covers related materials and specification choices.

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