Approved Document E — UK Sound Insulation Requirements Guide | AcousPlan

Approved Document E (ADE) is the UK Building Regulations guidance document that covers sound insulation between dwellings. First published in 1990 and significantly revised in 2003 (with a 2004 amendment), ADE sets out the legally required acoustic performance for separating walls and floors between new-build and converted residential properties in England and Wales. Scotland has equivalent provisions in Technical Standard Section 5 (Noise); Northern Ireland has similar requirements in Technical Booklet G.

This guide covers ADE requirements in detail: performance targets, measurement methods, the pre-completion testing regime, the Robust Details alternative, and the construction types that reliably achieve compliance.

The Legal Context

ADE derives its force from the Building Regulations 2010 (SI 2010/2214) — specifically Requirement E1 (Protection against sound from other parts of the building and adjoining buildings) and E2 (Protection against sound within a dwelling-house etc.). Building Regulations apply to:

• New residential buildings with two or more dwelling units separated by walls or floors
• Conversions of non-residential buildings to residential use
• Material change of use (e.g., office to apartment)
• Extensions that create new separating elements

Performance Targets

ADE requires a minimum level of acoustic performance, measured in the field after construction and before occupation (pre-completion testing, or PCT). The metrics used are:

DnT,w — Normalised level difference, weighted. Measures airborne sound insulation between rooms. Measured per ISO 16283-1.

DnT,w + Ctr — DnT,w with a low-frequency correction factor. The Ctr term penalises assemblies that perform poorly at low frequencies (typically 100–315 Hz), which affects assemblies that provide high STC-equivalent values through mass but poor low-frequency performance. ADE 2003 requires DnT,w + Ctr for walls.

L'nT,w — Standardised impact sound pressure level, weighted. Measures impact sound insulation for floors. Lower values are better. Measured per ISO 16283-2.

New Build — Separating Walls (Section 0, Table 1a)

Note: Some newer guidance documents and NHBC Standards specify DnT,w ≥ 45 (without Ctr) for walls where the Ctr value makes a material difference. Always reference the version of ADE in force at time of building control application.

New Build — Separating Floors (Table 1b)

Both the airborne and impact criteria must be met simultaneously.

Conversions — Separating Walls (Table 1c)

Conversions use the same performance targets as new build but recognise that existing building fabric may limit what is achievable:

• Walls: DnT,w + Ctr ≥ 43 dB (2 dB lower than new build to reflect existing construction constraints)
• Floors: DnT,w + Ctr ≥ 43 dB, L'nT,w ≤ 64 dB

The DnT,w vs Rw Distinction

A common source of confusion is the difference between DnT,w (in-situ field measurement) and Rw (laboratory measurement). They are measuring different things:

Rw (or R'w) is the laboratory sound reduction index — the acoustic property of the assembly alone, tested in a laboratory without flanking. It is a property of the product.

DnT,w is the in-situ normalised level difference — the actual performance measured in the completed building, including flanking transmission through the structure. It is a property of the installed system.

The relationship is approximately: DnT,w ≈ R'w − K, where K is a flanking correction factor typically 2–8 dB depending on structure type and flanking paths. This means an assembly with R'w = 50 dB (laboratory) may achieve only DnT,w = 43–48 dB in the field.

Design implication: Do not specify an assembly rated R'w = 45 dB and expect to meet DnT,w ≥ 45 dB. Build in a margin. For new build, specifying assemblies with R'w ≥ 52–55 dB provides reasonable confidence of achieving DnT,w + Ctr ≥ 45 dB after flanking.

Robust Details Scheme

The Robust Details (RD) scheme provides an alternative to pre-completion testing for new-build housing. Developers who register plots with Robust Details Ltd and construct exactly to an approved RD specification are deemed to satisfy ADE without PCT.

How it works:

1. Developer selects an approved RD specification from the RD Handbook (published annually by Robust Details Ltd)
2. Developer registers each dwelling unit on the RD website and pays the per-plot fee (currently £225 + VAT)
3. Robust Details Ltd issues a registration certificate
4. Construction must exactly follow the RD drawing package — no modifications
5. Building control accepts the RD certificate in lieu of PCT results

• Separating walls: masonry (E-WM-1 to E-WM-37), timber frame (E-WT-1 to E-WT-35), steel frame (E-WS-1 to E-WS-15)
• Separating floors: concrete (E-FC-1 to E-FC-28), timber (E-FT-1 to E-FT-35)

Limitations: Construction must exactly follow the RD specification — any deviation invalidates the registration. On-site variation is common (substituted materials, changed details) and creates liability. RD monitoring visits (approximately 5% of registered plots are inspected) can identify non-compliance and remove deemed-to-satisfy status retrospectively.

Cost comparison: RD registration at £225/plot is typically cheaper than PCT (£600–£1,200 per dwelling for a specialist acoustic tester), particularly for volume housebuilders.

Common Construction Types and Performance

Masonry Construction

Masonry separating walls remain the simplest way to achieve ADE compliance reliably. Performance depends primarily on mass per unit area.

Cavity masonry walls with mineral wool infill represent the gold standard for masonry ADE compliance and are included in several RD specifications.

Timber Frame Construction

Timber frame is more challenging for acoustic performance because the lightweight structure provides less mass and the timber skeleton bridges cavities, creating flanking paths.

Achieving DnT,w + Ctr ≥ 45 dB in timber frame construction almost always requires double stud framing — a single frame with resilient channels is insufficient due to flanking through the common plates.

Concrete Frame Construction

In-situ concrete construction provides high mass and relatively low flanking risk, making ADE compliance more straightforward.

For floors, the impact insulation (L'nT,w ≤ 62 dB) is the more challenging criterion. A 200mm concrete slab achieves L'nT,w of approximately 72–78 dB without soft floor finishes or a floating system — well above (worse than) the 62 dB maximum. A floating screed (50–65mm depth, resilient layer below) reduces L'nT,w to approximately 50–60 dB.

Pre-Completion Testing Process

When PCT is required (i.e., Robust Details is not used), the testing process follows BS EN ISO 16283-1 (airborne) and BS EN ISO 16283-2 (impact).

Finding an Accredited Tester

Testing must be carried out by an accredited tester registered with a UKAS-accredited body. The Acoustics Testing Service Register (maintained by ANC) lists accredited testers. Typical testing costs:

• Single apartment pair test (airborne wall): £400–£600
• Floor/ceiling test (airborne + impact): £600–£900
• Full floor plate of 10 apartments: £2,500–£4,500 (economies of scale)

Test Procedure

1. The tester brings a speaker, amplifier, and calibrated omnidirectional microphones
2. The speaker plays broadband noise (pink noise) in the source dwelling
3. Sound pressure levels are measured at multiple positions in the source and receiving dwellings
4. The normalised level difference (DnT) is calculated at each third-octave frequency from 100 Hz to 3,150 Hz
5. DnT values are combined using ASTM E413-equivalent weighting to produce DnT,w
6. The Ctr correction factor is applied: DnT,w + Ctr = ADE metric
7. Result is compared to the minimum requirement (45 dB for new build)

Consequences of Failure

If a test fails — DnT,w + Ctr < 45 dB for a wall, or L'nT,w > 62 dB for a floor — the developer must:

1. Investigate the cause (flanking, penetrations, workmanship defect)
2. Carry out remedial works (add drywall layer, install resilient channels, seal penetrations)
3. Re-test at the developer's cost

Flanking Transmission: The Primary Failure Mode

The majority of ADE test failures in both masonry and timber frame construction result from flanking transmission — sound bypassing the separating element through adjacent structural connections.

Most common flanking paths:

1. Intermediate floor to separating wall junction: In masonry construction, the concrete floor slab is often built continuously through the separating wall, creating a rigid bridge. This can reduce DnT,w by 5–10 dB relative to the theoretical prediction.

1. External cavity wall to separating wall: In cavity wall construction, the outer leaf of the external wall connects to the separating wall. Sound can travel from one apartment's external wall along the brickwork into the adjacent apartment.

1. Continuous ceiling void: In timber frame construction, a continuous ceiling void above two separating units allows sound to propagate along the void and re-radiate in the adjacent unit.

1. Service penetrations: Back-to-back electrical outlets, waste pipes penetrating the separating floor without acoustic collars, and unlined duct penetrations all create short-circuit paths.

Summary Table: ADE E1 Minimum Requirements

ADE compliance is achievable with standard construction when flanking is controlled and the separating assembly is appropriately specified. The most reliable path to compliance is to use Robust Details specifications where the project type and construction programme allow — they eliminate test risk and have a strong track record of delivering compliant performance in practice.

For projects that require PCT, engage an acoustic consultant at RIBA Stage 2 to review the proposed separating assemblies and flanking details before they are fixed in the design, rather than discovering failures after construction.