Approved Document E Explained: Sound Insulation Between Dwellings
Two housing projects can meet the same acoustic requirement through different compliance routes. One may use a registered separating wall or floor detail. The other may rely on measurements taken near completion. That early choice affects design freedom, procurement, site checks, testing costs and the amount of risk carried towards handover.
Approved Document E explains sound insulation between dwellings and other aspects of building acoustics. Kimber Acoustics advises project teams on the design and compliance implications, with Robert Kimber MIOA providing direct senior input.
What Is Approved Document E?
Approved Document E gives practical guidance on meeting Part E requirements for resistance to the passage of sound.
Approved Documents describe common ways to satisfy Building Regulations requirements. Alternative solutions may be used when the project team can provide suitable evidence. Building Control decides whether the submitted design and evidence meet the applicable requirements.
England and Wales publish separate national guidance. The English Approved Document E (gov.uk) covers dwelling-houses, flats, rooms for residential purposes and schools. Projects in Wales should use the current Welsh Approved Document E (gov.wales). The relevant version and any project-specific interpretation should be confirmed at the outset; however, there is currently no material difference in the residential acoustic requirements discussed here.
A striking atrium space with sweeping curved walkways and layered floors, the kind of multi-dwelling design where sound insulation between levels.
Which Sound Insulation Requirements Apply Between Dwellings?
Part E addresses four broad areas: sound from adjoining buildings and other parts of a building, sound within a dwelling, reverberation in communal internal areas, and acoustic conditions in schools. For houses and flats, separating walls and floors are usually the main focus, and the same requirements shape residential acoustic design from the earliest layout decisions.
Airborne And Impact Sound Targets
Airborne sound includes speech, television and music passing through or around a separating construction. Impact sound comes from direct contact with a floor, such as footsteps, and is assessed for separating floors and stairs.
The Approved Document E performance table (gov.uk) gives these on-site values:
| Dwelling Type | Minimum Airborne Performance, DnT,w + Ctr | Maximum Impact Performance, L'nT,w |
|---|---|---|
| Purpose-built houses and flats | 45 dB for separating walls, floors and stairs | 62 dB for separating floors and stairs |
| Houses and flats formed by material change of use | 43 dB for separating walls, floors and stairs | 64 dB for separating floors and stairs |
A higher airborne result is better. A lower impact result is better.
The Construction Works As A System
A wall or floor build-up cannot be assessed from its headline product alone. Mass, cavities, linings, resilient layers, junctions, penetrations and the connected structure all affect performance. This is why a familiar board or insulation product may be suitable in one build-up and ineffective in another.
How Do The Two Compliance Routes Compare?
For many residential developments, the practical choice is between Robust Details and Pre-Completion Testing. Both can support compliance, although they place cost, control and evidence at different points in the programme.
| Decision Factor | Robust Details | Pre-Completion Testing |
|---|---|---|
| Usual fit | Eligible new adjoined houses and flats | Conversions and projects using project-specific constructions |
| Evidence | Registration and construction to a published detail | Measurements from completed dwellings |
| Design freedom | Limited to the chosen registered detail | Greater freedom to develop a specific design |
| Main cost items | Registration, specified materials and site quality control | Acoustic design, test sets, access and programme allowance |
| Main control task | Keep procurement and workmanship aligned with the detail | Coordinate design, test groups, readiness and contingency |
| Main risk | A change may fall outside the registered specification | Performance is proved late in the programme |
Using Robust Details
Robust Details are registered separating wall and floor constructions for eligible new adjoined dwellings. The scheme’s plot registration guidance (robustdetails.com) excludes conversions, extensions and refurbishments. It also requires houses or flats to be registered before work starts and built to the chosen specification.
This route can give a repetitive new-build scheme a clear construction standard and a predictable inspection process. Control is the price of that predictability. A substituted block, changed cavity, different lining or altered junction can take the construction outside the registered Robust Detail. Where a change is not accepted within the detail, the affected plots may need to be removed from the Robust Details scheme and subject to pre-completion sound testing.
Using Pre-Completion Testing
Pre-Completion Testing measures the performance achieved in the finished building. It suits projects where a registered detail is unavailable or where the team needs more freedom over structure, materials and junction details.
The Approved Document E guidance for England and Wales (gov.uk) calls for the first property in every construction group or subgroup to be tested. If tests pass, Building Control should require at least one set for every ten houses, flats or rooms in each group or subgroup. A varied scheme may therefore need more test sets than a simple count of dwellings suggests.
Testing should be undertaken by an appropriately qualified body with appropriate third-party accreditation. Approved Document E states that test bodies should preferably have UKAS accreditation for field measurements and also regards members of The Association of Noise Consultants testing scheme (association-of-noise-consultants.co.uk) as suitably qualified to carry out pre-completion testing . Where another testing arrangement is proposed, its acceptability should be agreed with Building Control before testing is undertaken. Kimber Acoustics carries out sound insulation testing of walls and floors against Building Regulations, planning conditions and design targets, including preliminary testing during construction to check progress against the acoustic specification. Kimber Acoustics issues test reports for Building Control, BREEAM submission and client handover.
Where Does Part E Performance Commonly Weaken?
Acoustic performance can be lost through the main separating element and through indirect paths around it. The design and site inspection strategy should address both.
Mass, Resilient Layers And Substitutions
Increasing the mass of a partition can impede airborne transmission. Dense aggregate blocks or multiple plasterboard layers may form part of an effective design, provided the complete build-up and junctions are suitable.
Impact isolation relies on the resilient layer being continuous, correctly installed and not bridged by rigid connections. Rigid fixings through that layer, debris in the build-up or hard contact at the perimeter can create a path for vibration. Procurement changes should be reviewed before installation because matching thickness or appearance does not establish equivalent acoustic performance.
Gaps, Services And Flanking Paths
Flanking transmission occurs when sound travels through the façade, floor slab, internal walls, roof construction or another connected element. It bypasses some or all of the intended separating wall or floor.
Unsealed pipe and cable penetrations, incomplete perimeter seals, gaps behind skirting and back-to-back socket boxes can also reduce airborne performance. Once finishes conceal these details, diagnosis and remedial work become more disruptive. Early coordination should cover service routes, wall-to-floor junctions, floor edges, external walls, beams and roof interfaces.
Which Route Offers Better Cost And Project Control?
Neither route is always cheaper. The useful comparison is the whole compliance cost, including design input, registration, specified materials, procurement checks, inspections, testing, programme allowance and any investigation or retesting.
A repeated new-build design may suit Robust Details when the contractor can maintain close control over materials and workmanship. A conversion or unusual structure may justify the testing route because it preserves design freedom. Robert Kimber MIOA’s professional view is that the compliance route and acoustic design should be resolved before tender, with layouts, separating constructions and critical junctions sufficiently developed to avoid acoustic design being deferred into construction.
When A Site-Specific Review Helps
Generic guidance reaches its limit when eligibility, unusual junctions or proposed substitutions remain uncertain. Kimber Acoustics can review plans and separating constructions, identify likely flanking risks, advise on acoustic details and help define an appropriate testing strategy. That work sits within our building and architectural acoustics service.
At the Perfume Factory development in North Acton, a 450-apartment scheme bounded by a railway corridor and major road network, acoustic input ran from baseline surveys through planning, detailed design and condition discharge to commissioning. It included mitigation of flanking transmission within the building fabric alongside verification testing.
That advice supports the project team’s route decision. Building Control retains responsibility for accepting the compliance evidence.
What Happens If A Pre-Completion Test Fails?
A failed set of tests requires cause-led investigation. The Approved Document E guidance on failed tests (gov.uk) says suitable remedial treatment should address the cause of failure. It also allows Building Control to request evidence for similar untested rooms or dwellings and to increase the testing rate until the issue is resolved.
Work may involve opening finishes or removing skirting so perimeter gaps and service penetrations can be sealed. Structural flanking may require a project-specific lining or isolation detail. Further testing will normally be used to assess whether remedial treatment has worked. Diagnosis should come first, since treating a visible gap alone may leave another transmission path unchanged.
Getting The Compliance Scope Clear
As a former Robust Details inspector, Robert Kimber has first-hand understanding of how the scheme operates, the construction issues that commonly cause problems, and how to deal with situations where substitutions or departures from a registered detail result in affected plots being removed from the scheme and requiring pre-completion testing.
If you are choosing a Part E route, share the site plans, proposed wall and floor build-ups, new-build or conversion status, plot types, programme constraints and any Building Control comments. Robert Kimber personally reviews and scopes each enquiry, retains senior oversight through assessment and technical advice, and will recommend a proportionate level of acoustic consultancy support.