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adding soundproofing to an extension

UK Homeowners: Avoid 80–100mm Loss When Soundproofing an Extension

Practical steps for UK homeowners to soundproof an extension. Specify airtight linings, add mass and decoupling at design stage to avoid costly retrofits...

The Extension Works 23 September 2026
UK Homeowners: Avoid 80–100mm Loss When Soundproofing an Extension

UK Homeowners: Avoid 80–100mm Loss When Soundproofing an Extension

Acoustic wall layers inside a rear extension

The most reliable way to soundproof an extension is to combine added mass, airtight sealing and, where the noise is severe, a decoupled lining rather than relying on insulation alone. Party walls and shared floors need more work than internal partitions, and specifying these measures during the build is almost always cheaper and less disruptive than retrofitting them afterwards.

TL;DR:

  • Adding mass and decoupling during construction offers the most cost-effective way to significantly reduce both airborne and structureborne noise.
  • Sealing gaps around sockets, junctions, and at every joint can improve noise reduction more than expensive wall upgrades alone.
  • Materials like mismatched plasterboard layers and mineral wool in cavities enhance soundproofing, especially against mid to high frequencies.
  • Retrofit solutions such as resilient clip systems and secondary glazing work but may reduce room depth and require careful installation.
  • Soundproofing must be specified at the design stage for best results and compliance, especially for separating walls between dwellings.
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Table of Contents

Prioritised methods: mass, decoupling, damping and sealing

Get the order of operations wrong and you will spend money on the wrong fix first. Sound control works in layers, and each layer solves a different problem.

Mass stops airborne noise, the sort that travels through the air (voices, television, traffic). Doubling up plasterboard layers, or adding a sheet of mass loaded vinyl (MLV) between boards, gives sound waves more material to push through before they reach the other side. It is the single cheapest upgrade you can make to a stud wall.

Decoupling deals with structureborne noise and bass, the low-frequency thump that mass alone struggles to stop. An independent stud wall, or resilient clips and channels fixed to the existing structure, breaks the physical path sound uses to travel through timber and masonry. This is where most of the improvement in bass reduction comes from.

Damping uses a viscoelastic compound sandwiched between two rigid boards to convert vibration into heat rather than letting it pass through. It gives the biggest gain when applied to an existing wall you cannot easily decouple, such as a shared party wall you are not rebuilding.

Sealing is the cheapest and most neglected step. Acoustic sealant around skirting, putty pads behind electrical sockets, and proper sealing at every junction close the gaps that let sound leak straight past your expensive wall build-up.

  • Quick wins: acoustic sealant, socket pads, secondary glazing, an extra layer of plasterboard
  • Comprehensive rebuilds: independent stud walls, resilient clip and channel systems, full MLV build-ups

Pro Tip: Fit acoustic putty pads behind every socket and switch on a party wall before boarding. A single unsealed back box can undo the benefit of an otherwise well-built wall.

What materials and build details actually work

Specifying materials correctly matters more than the brand name on the bag. Mineral wool (Rockwool or similar) at 100mm density in a stud cavity absorbs mid and high frequencies effectively and costs little compared with the boards around it.

For plasterboard, two layers staggered with different thicknesses (commonly 12.5mm and 15mm) outperform two identical sheets, because mismatched panels resonate at different frequencies rather than reinforcing each other. Adding a 10kg MLV layer between boards, as used in the Advanced Acoustics pro independent wall soundproofing system, brings the whole build-up to around 80mm and is aimed at genuinely loud, persistent noise rather than everyday household sound.

What materials and build details actually work — overview diagram

Resilient clip systems sit between basic mass upgrades and full independent walls. The AcoustiClip direct-to-wall system reports a tested reduction of up to 63dB on a specific brick wall construction, at a system depth of roughly 77mm. That figure applies to a particular wall type under manufacturer test conditions, so always ask a supplier to confirm expected performance for your actual wall build before you commit.

Windows and doors deserve equal attention:

  • Secondary glazing, particularly with a wider air gap and acoustic laminate, often beats new double glazing for noise reduction, and Historic England’s guidance on secondary glazing notes it needs adequate ventilation to avoid condensation between the panes.
  • Solid-core doors with compression seals close another common leak point, and door options built for noise reduction show how much a hollow internal door undermines an otherwise sound-treated room.

When to add soundproofing: build stage versus retrofit

  1. Specify it during the build. Insulation, lining choices and window selection get baked into the design and price, and there is no need to strip out finished walls later.
  2. Retrofit when the extension already exists. Direct-bond boards, clip and channel systems, and secondary glazing all work, but expect some loss of room depth (typically 80 to 100mm per treated wall) and a full re-decorate afterwards.
  3. Call in a survey when noise is severe or the property is listed. An acoustician can measure the actual problem frequency rather than guessing, which avoids paying for a fix that targets the wrong type of noise.

Building regs and compliance: what Part E actually requires

Approved Document E governs resistance to the passage of sound, and it matters more than most homeowners expect once an extension creates a new separating wall or floor between dwellings.

  • Part E applies to separating walls and floors between dwellings or between a dwelling and another residential space, not to ordinary internal partitions within your own home.
  • Pre-completion testing is generally required for new dwellings or material changes of use, with at least 10% of new dwellings tested under Part E guidance; most single-storey rear extensions to an existing house fall outside this testing requirement.
  • Guidance documents reference example laboratory targets, such as an Rw of around 40dB for internal partitions, as a benchmark for demonstrating reasonable resistance to sound.
  • If your extension does create a separating element, involve building control early and keep a written record of the construction details used, since you carry the responsibility to demonstrate compliance.

For period or listed properties, Historic England’s guidance on managing change favours acoustic measures that avoid damaging historic fabric, which usually means secondary glazing and non-invasive linings over invasive structural changes.

DIY versus hiring a specialist: what to take on yourself

Sealing gaps, adding cavity insulation, and fitting secondary glazing are all realistic DIY jobs if you are reasonably competent with basic tools. Resilient channel installation, any structural alteration, acoustic testing, and rerouting services behind a new lining are specialist territory, because a poorly fixed channel system can perform worse than no treatment at all.

Persistent bass problems, or any work on a listed building, are red flags that should send you to a qualified acoustician or an experienced contractor rather than a general builder. Before hiring anyone, ask for the specific system they intend to use, its tested performance figures, and how they plan to treat electrical outlets and junctions.

Pro Tip: If a contractor cannot name the acoustic system they are quoting for, or point you to its manufacturer test data, treat that as a warning sign, not a minor detail.

DIY versus hiring a specialist: what to take on yourself — overview diagram

Applying this in a managed rear-extension project

Sound control works best when it is decided at the same time as your windows, wall build-up and room layout, not bolted on afterwards. The Extension Works builds insulation and lining choices into the design and pricing stage of every single-storey rear extension it manages, so the specification, sequencing and finishing all sit under one fixed, VAT-inclusive price and a 12-month workmanship warranty, rather than being handed between separate trades.

Homeowner perspective: realistic expectations and trade-offs

Perfect silence is not on offer at any sensible budget. The honest goal is a noticeable, liveable reduction, and sealing every gap properly usually delivers more for your money than the priciest board on the market. Decisions made before first fix matter far more than anything added afterwards.

— Esskay

Get a fixed-price quote that specifies soundproofing from day one

A managed service that avoids piecing together separate acoustic products and trades uses one in-house team to specify wall build-up, windows and insulation together, building to a fixed, VAT-inclusive price with a workmanship warranty to reduce risk of omissions at handover.

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Retrofitting sound control after the plasterers have gone home almost always costs more and disrupts your finished rooms. Get an instant online quote that bakes acoustic specification into the design from the outset, or check the booking process and fees to see how sequencing works before your extension starts on site.

Sources

FAQ

Can you soundproof a room from noisy neighbours?

Yes, though results depend on whether the noise is airborne (voices, TV) or structureborne (bass, footsteps). A combination of added mass, decoupling and thorough sealing gives the biggest improvement, and a resilient clip system such as AcoustiClip can reach tested reductions of up to 63dB on suitable masonry walls.

How can I stop sound travelling between floors in my house?

Impact noise between floors responds best to a floating floor with a resilient underlay, which breaks the path vibration takes into the joists below. Sealing skirting boards and pipe penetrations around the floor perimeter adds a further, low-cost improvement.

Approved Document E requires new separating walls and floors between dwellings to give reasonable resistance to sound, but it does not apply to ordinary internal partitions within a single home. Most single-storey rear extensions fall outside pre-completion testing requirements unless they create a new separating element between dwellings.

How can I block noise from a shared wall?

Start with airtight sealing around every socket, skirting board and junction, since gaps undermine even the best board build-up. For persistent or bass-heavy noise, add mass with an extra plasterboard layer and MLV, or move to a decoupled system like MuteClip clips if the noise remains a problem after sealing and mass alone.

What does The Extension Works charge to include soundproofing in an extension?

Soundproofing specification is built into the design and pricing of every project rather than sold as a separate add-on, so there is no separate published figure for it. Homeowners can get a fixed, VAT-inclusive price for the whole extension, including material choices, through the instant quote tool.