Acoustic Underlay & Soundproof Flooring

Noise travelling through floors, footsteps, dropped items, muffled voices from below, is one of the most common complaints in UK homes, particularly in flats and Victorian terraces with timber joists. The most practical and affordable first step is a quality acoustic underlay fitted beneath your chosen floor covering. Done correctly, it can make a measurable difference without lifting floorboards or pouring concrete.

Acoustic underlays work on two distinct sound paths: impact sound (vibrations travelling through the structure itself, like footsteps) and airborne sound (voices, music passing through air gaps). Most products target impact sound, which is where underlay has the greatest effect. For airborne noise you generally need a combination of mass and decoupling, underlay alone will not stop sound carrying between flats.

How Sound Reduction Is Measured

Impact sound improvement is expressed as ΔLw (delta Lw) in decibels, the higher the number, the better the product. A ΔLw of 20 dB roughly halves the perceived loudness of footstep noise.

Building Regulations Part E sets minimum standards for new-build flats and houses converted into flats:

The two figures come as a pair and the pair depends on how the flats were made:

• Purpose built separating floor: impact L’nT,w ≤ 62 dB, airborne sound insulation DnT,w + Ctr ≥ 45 dB¹
• Formed by a material change of use, which is what a house split into flats is: impact L’nT,w ≤ 64 dB, airborne DnT,w + Ctr ≥ 43 dB

Mixing 62 with 43 is the common slip, and it is the combination that appears in neither column

If you are converting a house into flats in England, you must demonstrate compliance with Part E. An acoustic underlay alone is rarely sufficient, you will typically need a floating screed, resilient batten system, or specialist acoustic floor build-up tested to Part E. Speak to an acoustic consultant before starting conversion work.¹

For owner-occupiers improving sound comfort within their own home (e.g., reducing noise between floors in a house), Building Regs do not apply, and a good underlay can deliver a satisfying improvement.

Types of Acoustic Underlay

Foam underlays are the cheapest option but offer modest acoustic performance. They compress quickly under point loads, reducing effectiveness within a year or two.

Crumb rubber (often from recycled tyres) strikes a good balance of performance and cost. It is resilient, does not compress significantly under furniture, and works well under floating engineered boards.

Recycled felt (shoddy felt) is a popular choice under carpet and solid wood. It provides warmth underfoot and good mid-range acoustic performance but can absorb moisture in poorly ventilated spaces.

Cork is a natural option with reasonable impact reduction and thermal insulation. It works best under rigid boards and is worth considering in rooms where thermal performance matters.

Combination products laminate rubber with foam or felt to achieve the highest residential ΔLw figures. These are the go-to choice if you are trying to maximise impact sound reduction without structural intervention.

Acoustic mats (dense loaded vinyl or mineral-filled products) are primarily designed as part of a tested system for Building Regs compliance. They are thicker and heavier than standard underlays and require careful specification.

Acoustic Underlay for Different Floor Types

Laminate & Engineered Wood (Floating)

Look for an underlay with a combined thickness (underlay + floor) that does not exceed the floor manufacturer’s specification, typically underlay should be no thicker than 3–5 mm for most floating systems. Exceeding this can void the floor warranty. A crumb rubber or combination product at 5 mm is often the sweet spot.

Solid Wood (Glued or Secret-Nailed)

If gluing or nailing solid boards to a subfloor, a thin acoustic mat (2–3 mm) can be bonded beneath the boards. Thick compressible underlays are not suitable as they create movement under fixed floors.

LVT (Luxury Vinyl Tile / Plank)

Many LVT products have a pre-attached underlay. Adding a second layer can cause excessive flex and damage click joints. Check manufacturer guidance, some allow a 1–1.5 mm acoustic underlay; most rigid-core LVT does not.

Carpet

Carpet underlay is traditionally sold for comfort, but many products also carry useful acoustic ratings. A recycled felt or PU foam product at 8–10 mm will outperform a thin foam on impact noise. Combined carpet and underlay systems can achieve ΔLw of 25–32 dB.

What Affects the Cost?

The main cost driver is the ΔLw rating and material quality. At the budget end, a 3 mm polyurethane foam underlay for a 20 m² room will cost roughly £40–£80 in materials alone. A high-performance 10 mm combination product for the same area runs £120–£240.

For a typical 20 m² living room:

Most acoustic underlays are straightforward to lay yourself, cut to size with scissors or a knife, butt-join without overlapping, and tape joins with the manufacturer’s recommended tape.

When Underlay Alone Is Not Enough

If you live in a flat and your neighbour’s footsteps are clearly audible, underlay will help but is unlikely to eliminate the problem. For significant improvement you typically need:

• Floating floor system, floor boards on resilient cradles or battens, decoupled from the structure
• Floating screed, 65–75 mm sand-cement or anhydrite screed on acoustic insulation quilt (adds significant mass)
• Ceiling treatment below, independent ceiling on resilient bars, or acoustic ceiling tiles, to address the flanking path

These systems cost £25–£80/m² installed and require structural assessment. An acoustic engineer (typical fee £500–£1,500 for a flat) can specify a compliant solution and may save you money by avoiding over-specification.

Key Things to Check Before Buying

1. ΔLw rating, confirm the figure is independently tested, not just a manufacturer claim.
2. Compatibility with your floor, check the floor manufacturer’s underlay thickness limit.
3. Moisture barrier, if your subfloor is concrete, choose an underlay with a built-in DPM (damp-proof membrane) or use a separate 250 µm polythene sheet.
4. Underfloor heating (UFH) compatibility, acoustic underlays with high tog values will impede heat transfer. For UFH, look for underlays rated below 0.15 m²K/W (thermal resistance) and confirm UFH compatibility explicitly.
5. Part E testing, if you need Building Regs compliance, only use products that form part of a tested system with published test data.¹

A well-chosen acoustic underlay is one of the highest-value improvements you can make for floor noise, affordable, quick to install, and immediately noticeable underfoot.