How Sound Insulation Testing Works

Part E of the Building Regulations requires pre-completion sound insulation testing on all new residential developments and conversions. Understanding how the test works – and what affects the result – is essential for contractors and developers aiming for a first-time pass.

A sound insulation test measures how well a separating wall or floor resists the transmission of sound between two adjoining spaces. Tests are carried out by a qualified acoustic engineer after all finishes are complete but before carpets are laid. Each test places a loudspeaker in one room and measures sound levels in both the source and receiving rooms; the difference, adjusted for the room’s reverberation characteristics, produces the test result.

Two types of test are required under Part E:

Airborne Sound Testing

Airborne tests measure resistance to sounds carried through the air – voices, television, music. The result is expressed as DnT,w+Ctr in decibels. The Part E minimum for walls and floors between new dwellings is 45 dB – higher values indicate better performance.

Impact Sound Testing

Impact tests apply to floors only and measure resistance to sounds generated by physical contact – footsteps, dropped objects. A standardised tapping machine strikes the floor while microphones measure the transmitted level below. The result is expressed as L’nT,w in decibels. The Part E maximum for new dwellings is 62 dB – lower values indicate better performance.

The number of tests depends on development size, type, and whether Robust Details have been used. Under the standard regime, a minimum of one set of tests is required for every ten dwellings of each type. Each full set consists of two floor tests (airborne and impact) and two wall tests (airborne). Agree the test programme with building control before work starts – they have discretion to require additional tests.

Where Robust Standard Details (RSDs) are used for all separating elements, reduced sampling is permitted. RSDs cover a range of masonry, timber frame and steel frame construction types. If any non-RSD element is present, full testing applies to those elements.

The most frequent cause of failure is flanking transmission – sound travelling via indirect paths through connected structural elements rather than through the separating element itself. Common failure points include concrete floor slabs running continuously through separating walls, poorly fitted resilient layers, gaps at separating wall junctions, and inadequate acoustic floor screeds.

Build Energy carries out pre-completion acoustic surveys to identify likely failure points before the formal Part E test. Remediating problems before testing is substantially cheaper than failing, remedying, and re-testing – and avoids delays to building control sign-off.

A failed element must be remediated and re-tested before building control can issue a completion certificate. Common remediation routes include additional acoustic floor screed, sealing gaps at separating wall junctions, or additional resilient layers. Build Energy advises on remediation strategies and carries out re-tests across England and Wales.

For sound insulation testing services, see Sound Insulation Testing. For acoustic design advice, see Acoustic Consultancy. Return to the Acoustics hub.

What is airborne sound insulation?

Airborne sound insulation measures how well a separating element (wall or floor) resists the transmission of airborne sounds – voices, television, music and similar. It is expressed as DnT,w+Ctr in dB; higher values indicate better performance. The Part E minimum for new dwellings is 45 dB.

What is impact sound insulation?

Impact sound insulation measures how well a floor resists the transmission of impact sounds – footsteps, dropped objects and similar. It is expressed as L’nT,w in dB; lower values indicate better performance. The Part E maximum for new dwellings is 62 dB.

What are Robust Standard Details (RSDs)?

Robust Standard Details are pre-tested construction details approved by the government for use in new-build residential developments in England. If a developer uses a registered RSD for all separating elements, reduced sound insulation testing (sampling) is permitted. RSDs cover a range of wall and floor types for masonry, timber frame and steel frame construction.

Can flanking transmission cause a sound insulation test failure?

Yes. Flanking transmission – sound travelling via indirect paths around a separating element through connected structural elements – is one of the most common causes of Part E test failures. It typically occurs through concrete floor slabs, connecting masonry walls, or lightweight steel framing. Build Energy advises on flanking control at design stage.

What equipment is used for sound insulation testing?

Sound insulation tests use calibrated loudspeakers, microphones and sound level meters conforming to ISO 10140. Build Energy uses equipment that meets the requirements of ISO 140 and Approved Document E for all site measurements.