Building Regs Part E (Sound) Explained — A 2026 Compliance Guide for UK Trades

What Part E Actually Covers

Approved Document E supports Part E of Schedule 1 to the Building Regulations in England. It sets out requirements in four areas, and it helps to know which ones bite on your job:

• E1 — Protection against sound from other parts of the building: the separating (party) walls and floors between dwellings, and between dwellings and other parts of the same building. This is the headline requirement and the one that gets tested.
• E2 — Protection against sound within a dwelling: internal walls between a bedroom or a room containing a WC and other rooms, and internal floors. These are not tested, but they have a laboratory performance standard the construction must meet.
• E3 — Reverberation in the common internal parts of buildings containing flats: stairs, corridors and entrance halls need sound-absorbing treatment.
• E4 — Acoustic conditions in schools: at a high level, schools have their own acoustic requirements set out separately, so any conversion or new build for education has additional standards to meet.

Approved Document E is the guidance for England. Wales, Scotland and Northern Ireland each have their own equivalent. Wales uses its own version of Approved Document E, Scotland deals with noise under Section 5 of its Technical Handbooks, and Northern Ireland addresses it under Technical Booklet G. The principles are similar everywhere, but the exact figures and test regimes differ, so always work to the document for the nation the job is in.

The Performance Standards in Plain Terms

Part E is a performance-based requirement. It does not tell you exactly how to build — it tells you the result your construction has to achieve. There are two things being measured on separating elements:

Airborne sound insulation — how well a wall or floor stops voices, TV and music passing through. This is measured as a DnT,w + Ctr value in decibels, where higher is better. For separating walls and floors between dwellings in purpose-built (new build) homes, the standard is at least 45 dB. For walls and floors formed by a conversion of an existing building, the bar is slightly lower at a minimum of 43 dB, because you are working with an existing structure. The Ctr term is a correction that accounts for low-frequency noise such as bass — it makes the standard harder to meet and is the reason a wall that "sounds fine" can still fail.

Impact sound insulation — how well a floor stops footsteps, dropped objects and furniture being dragged. This is measured as L'nT,w in decibels, and here lower is better because you want less sound transmitted. For new build separating floors the maximum is 62 dB; for floors created by conversion the maximum is 64 dB. Impact sound only applies to floors, not walls.

Internal walls and floors under E2 have a single laboratory airborne figure to meet (Rw 40 dB) and are demonstrated by construction rather than by site testing. The key thing to remember: separating elements are judged on what they achieve on site after everything is built, including the effect of the surrounding structure.

Where and When Part E Is Triggered

Part E applies whenever you create a separating element between dwellings or rooms used for residential purposes. The common triggers on trade jobs are:

• New build flats and apartments — every separating wall and floor between units.
• Converting a house into flats — the new walls and floors that divide the property into separate dwellings.
• Change of use to residential — turning a shop, office, barn or pub into flats or houses brings the separating elements into scope even if no new walls are built, because the use has changed.
• Houses in multiple occupation (HMOs) — rooms for residential purposes, such as bedsits with separating walls and floors, fall under Part E. This catches a lot of landlords and conversion specialists who assume Part E is only about flats.
• Material alterations that affect existing separating elements.

A single dwelling house being refurbished for the same family generally does not trigger E1 testing, because there are no separating elements between dwellings. The moment you split occupancy — two flats, a granny annex that is a separate dwelling, or HMO rooms — Part E is live.

How Compliance Is Demonstrated: Testing vs Robust Details

There are two routes to show building control that a new build separating element meets Part E, and choosing the right one early saves money and risk.

Pre-completion sound testing

This is the default route. An accredited tester (UKAS-accredited or a member of a scheme recognised by building control) attends near the end of the job and carries out on-site measurements of airborne insulation on walls and floors, plus impact insulation on floors, using the relevant BS EN sound testing standards. A proportion of the separating elements in the development is tested — building control will agree the sample, typically a set number per construction type and per group of units. If the elements pass, you have your evidence. If they fail, you have to find and fix the problem and re-test, which means returning to finished rooms.

Testing applies to conversions too. For a house-to-flats conversion or a change of use, pre-completion testing is normally the only route — Robust Details are a new-build scheme and do not apply to conversions.

Robust Details (new build only)

For new build attached dwellings you can avoid pre-completion testing altogether by using a Robust Detail. Robust Details Ltd publishes a handbook of separating wall and floor constructions that have been tested extensively and shown to perform well above the Part E minimum, with margin built in to cover normal site variation. If you register the plot with Robust Details Ltd, pay the per-plot fee, and build exactly to the specified detail, building control accepts that as compliance without a sound test.

Robust Details registration must happen before work starts on the relevant plots. You receive a purchase statement and plot numbers, and the site must build precisely to the chosen detail — substituting a different plasterboard, mineral wool density or floor build-up voids the detail. The trade-off is simple: a registration fee and strict adherence to a prescribed detail, in exchange for no testing risk at completion.

Who Arranges and Pays for Testing

On most jobs the responsibility for arranging and paying for sound testing sits with the person carrying out the building work — usually the builder, developer or main contractor, not the building control body. Building control sets the requirement and agrees the testing schedule; you book and pay the accredited tester. On a developer-led scheme the developer carries the cost; on a small conversion the builder commonly prices it into the job. Either way, the cost and the programme time for testing — and for any remedial work and re-test — should be in your quote and your build programme from day one, because a failed test at the end is expensive and embarrassing if no one budgeted for it.

Build the test into your sequence: schedule it once finishes are in but with enough float to fix and re-test before handover. Testing too early gives misleading results; testing too late leaves no room to remedy.

How Part E Interacts With Building Control

Part E compliance runs through your building control application, whether that is the local authority or an approved inspector. Discuss the route at the outset: confirm whether you are going down the testing route or using Robust Details, and agree the testing sample if testing applies. Building control will want to see the test results or the Robust Details purchase statements as part of signing off the work. No evidence, no completion certificate — and on flats and HMOs that can stall sale, mortgage and occupation. Treat the sound evidence as a deliverable on the same footing as the electrical certificate or the air-tightness result.

Build Details That Pass

Part E performance comes from the whole assembly working together — mass, isolation, absorption and airtightness. The details that consistently pass share the same principles. For drylining and plastering contractors and joiners, these are the things that matter on site:

• Independent / twin walls: two separate leaves with no rigid connection between them stop sound bridging across. Independent linings on an existing masonry party wall are a common conversion fix.
• Resilient bars: mounting plasterboard on resilient metal bars rather than fixing it directly to studs or joists decouples the board and improves both airborne and impact performance. Long screws that bridge the bar back to the timber kill the benefit entirely.
• Acoustic mineral wool: the correct density of mineral wool in the cavity or between joists absorbs sound. Wrong density or no wool at all is a frequent failure.
• Floating floors: a floating screed or batten system on a resilient layer isolates the walking surface from the structure and is key to hitting the impact standard.
• Sealing flanking paths: sound travels around an element as much as through it. Seal the perimeter, fill gaps at wall-floor junctions, use flexible sealant at edges, and avoid rigid mortar bridges between leaves.
• Correct plasterboard spec: the number of layers, board mass and board type are specified for a reason. Substituting a thinner or lighter board is one of the most common causes of failure.

For E3, reverberation in common parts of blocks of flats is dealt with by adding sound-absorbing material — typically an absorbent ceiling treatment in entrance halls, corridors and stairwells — rather than by testing. Plan it in so it is not forgotten at the end.

Common Failures

When elements fail a Part E test, the cause is almost always one of a handful of recurring issues. Knowing them lets you design them out:

• Flanking transmission: sound travelling through the surrounding structure — continuous floor screeds, junctions, services and the inner leaf of an external wall — bypassing the separating element. This is the single biggest reason good-looking walls and floors fail on site.
• Gaps and penetrations: service holes, sockets fixed back-to-back, recessed downlights, unsealed perimeters and poorly filled junctions. Even small gaps wreck airborne performance.
• Wrong plasterboard spec: too few layers, the wrong board, or board that is too light for the detail.
• Skipped acoustic detail: resilient bars short-circuited by long fixings, mineral wool of the wrong density or left out, a floating floor battened straight to the structure, or a Robust Detail built "close enough" rather than exactly.

The pattern is consistent: Part E is unforgiving of shortcuts. A wall that is 99% right but has a sealed-perimeter gap or a hard bridge between leaves can still fail. Build the detail in full, every time, and you keep the test as a formality rather than a gamble.

Quick Reference: Part E Elements and What's Required

Figures are the England headline standards under Approved Document E and are given as a guide — always work from the current edition for the nation the job is in.

Frequently Asked Questions

Does Part E apply to a loft conversion in a single house?

Not for E1, if the house stays one dwelling for one household — there are no separating elements between dwellings. E2 internal sound requirements can still apply to new internal walls and floors. The moment the property is split into separate dwellings or used as an HMO, E1 is triggered.

Can I use Robust Details for a conversion?

No. Robust Details is a new-build scheme. Conversions and changes of use are demonstrated by pre-completion sound testing, so budget the test and remedial float into the job.

Who pays for the sound test?

The person carrying out the work — usually the builder or developer — arranges and pays for the accredited tester. Building control sets the requirement and agrees the sample but does not carry out or fund the test. Price it into the job.

What happens if an element fails the test?

You must find the cause, carry out remedial work and re-test. Because testing happens late, this can mean returning to finished rooms — which is exactly why getting the detail right first time, or registering Robust Details up front, matters so much.

Is Part E the same across the UK?

The principle is the same, but the documents differ. England and Wales each use their own Approved Document E; Scotland covers it under Section 5 of the Technical Handbooks; Northern Ireland under Technical Booklet G. Work to the right one for the job's location.