Noise through floors causes more disputes in London flats than almost anything else. It is also one of the few building problems you can substantially fix with the right flooring specification. This guide explains the two kinds of noise, the numbers used to measure them, and how to build a floor that performs.
Impact noise versus airborne noise
Impact noise is footsteps, dropped objects, chair legs and children running — energy transmitted directly into the structure. It is the type that causes complaints, and it is the type that flooring choice most affects.
Airborne noise is voices, television and music travelling through the air and then through the floor structure. Flooring helps with it far less; airborne performance is mostly determined by the mass and construction of the floor itself, and improving it usually means adding a resilient ceiling below rather than changing the covering above.
This distinction matters when you are buying underlay. A product advertised with a large decibel reduction figure is almost always quoting impact noise. If your problem is hearing conversations from the flat below, a new underlay will disappoint you.
The numbers: ΔLw, LnT,w and what they mean
Underlay performance is usually quoted as ΔLw — the improvement in impact sound insulation the product provides, measured in decibels. A budget foam underlay might offer 15–18 dB; a good acoustic underlay offers 20–24 dB; a high-performance rubber or composite system can reach 28 dB or more.
Building Regulations Part E sets the requirement for conversions and new dwellings in England: for separating floors, impact sound must not exceed 62 dB LnT,w in converted buildings, tested on site. Note that this is a whole-floor figure, not an underlay figure — the underlay contributes to it but does not determine it alone.
Because it is a site-tested figure, a manufacturer's ΔLw claim is not a guarantee of compliance. In a conversion subject to Part E, the sensible route is to use a system with published test data for a floor construction similar to yours.
- ΔLw 15–18 dB: standard foam underlay, domestic use only
- ΔLw 19–23 dB: genuine acoustic underlay, suitable for most leasehold flats
- ΔLw 24 dB+: high-performance systems for Part E conversions
- Part E conversion limit: 62 dB LnT,w, tested on site
What your lease probably says
Most London leases for flats above ground floor contain a clause requiring floors to be carpeted, or requiring the leaseholder to obtain consent before replacing carpet with a hard floor. These clauses are enforceable, and freeholders do enforce them when a downstairs neighbour complains.
Where consent is required, it is usually granted on condition that a specified acoustic underlay is used. Getting that consent in writing before you fit is far easier than arguing afterwards, and it costs nothing but a letter.
If you are buying a flat and intend to fit hard flooring, check this clause during conveyancing. Discovering after completion that your flat must stay carpeted is a common and entirely avoidable disappointment.
Build-ups that work
Carpet on a good PU underlay remains the best-performing and cheapest acoustic floor by a distance. Nothing else absorbs impact energy as effectively at the point it occurs. If noise is the priority and the aesthetics allow it, this is the answer.
For hard flooring, the effective build-up is a resilient acoustic layer between the floor covering and the structure — typically a 3–5mm rubber crumb or high-density composite mat. With LVT this can be a glue-down acoustic backing board; with click flooring it is an acoustic underlay laid loose.
Two details make or break the result. First, the resilient layer must be continuous, with no gaps at joints. Second, and most commonly missed, the floor must not touch the walls: any rigid contact at the perimeter creates a flanking path that bypasses the underlay entirely. Leave the expansion gap, and use a perimeter isolation strip in a serious installation.
Practical extras
Skirting boards should not sit hard down onto a floating hard floor. A 2mm gap, or scotia beading fixed to the skirting rather than the floor, preserves the acoustic break and prevents squeaks.
Doorway thresholds are another flanking route. A metal trim screwed through the floor into the subfloor connects the two structurally; a trim that sits on a resilient bed does not.
Rugs in traffic lanes give a further real-world improvement that no test figure captures — and in a flat where a hard floor has already caused friction with a neighbour, they are a fast, cheap way to defuse it.
Finally, be realistic. An acoustic underlay under LVT in a Victorian conversion will substantially reduce footfall noise, but it will not make a hard floor quieter than carpet. If the neighbour below is sensitive and the structure is lightweight timber, carpet remains the safest choice.
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Frequently asked questions
What is the best acoustic flooring for a flat?
Carpet on a quality PU underlay performs best. Where a hard floor is wanted, LVT or engineered wood over a 3–5mm rubber crumb or high-density acoustic underlay, with a perimeter gap to prevent flanking, is the effective option.
Can I put a hard floor in a leasehold flat?
Check the lease first — many require carpet above ground floor or written consent for hard flooring, usually conditional on a specified acoustic underlay. Get consent in writing before fitting.
What dB rating do I need in acoustic underlay?
For a typical leasehold flat, an underlay offering 19–23 dB ΔLw impact improvement is a sensible target. Conversions subject to Building Regulations Part E must achieve 62 dB LnT,w for the whole floor, tested on site.
Does acoustic underlay stop voices from below?
Not really. Underlays address impact noise such as footsteps. Airborne noise like speech and television depends on the mass of the floor structure and usually needs work on the ceiling below.