Acoustic services - frequently asked questions

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Basic Principles

What is sound insulation?

Sound insulation provides resistance to the passage of sound. In buildings sound can be defined as 'airborne sound' (i.e. sound generated and transferred directly in the air by talking or home entertainment systems) or 'impact sound' (i.e. sound generated by the impact of an object striking the floor and transmitted through it, such as footfall noise).

What is sound insulation testing in buildings?

A method of quantifying the resistance to the passage of sound provided by an element of the building (e.g. a wall or floor which separates different dwellings, hotel rooms etc. from each other, or a façade which insulates occupants from external noise).

What is flanking sound?

Sound that travels directly through a construction element separating two spaces (e.g. a separating wall between two flats) is referred to as 'direct sound transmission'. However, sound may also travel between spaces via other paths (e.g. via an adjoining external/internal wall) and this is referred to as 'flanking sound transmission'.


Why carry out sound insulation testing in buildings?

Building Regulations require that builders demonstrate the sound insulation performance of separating walls/floors in new-build dwellings or rooms for residential purposes (as well as those newly formed by a material change of use) where they are attached to another dwelling/building or part of the same building not exclusively used by the same occupants.

The regulations set minimum performance requirements for sound insulation between spaces so as to provide reasonable conditions for living. Performance can be demonstrated either by testing a sample of as-built constructions/properties or (in England, Wales & Scotland) by registering to use Robust Details.

Sound insulation testing may also be required in non-residential buildings (e.g. schools, hospitals, workplaces), where as-built performance needs to be demonstrated to ensure noise sensitive areas (e.g. classrooms, wards, meeting rooms) are suitably insulated from noisier areas.

What are the applicable Regulations?

England & Wales

Approved Document E 2003 (incorporating 2004 amendments) sets out the applicable regulations for England and Wales.

  • Requirement E1 covers  the requirements for protection against sound from adjoining buildings or other parts of the same building
  • Requirement E2 covers the protection against sound within a dwelling
  • Requirement E3 covers reverberation in common internal parts
  • Requirement E4 covers acoustic conditions within schools.


Section 5 of the Scottish Building Standards 2010 sets the sound insulation requirements for Scotland.

Standard 5.1 deals with separating walls and floors

Standard 5.2 deals with internal walls and floors.

Northern Ireland

Part G of the Northern Ireland Building Regulations contains the regulations for Northern Ireland.

Parts G1, G2 and G3 deal with separating walls and floors.

Credit based schemes

Schemes like the Code for Sustainable Homes offer credits within their assessment process for undertaking a sound insulation testing regime and further credits where measured performance exceeds the Building Regulations minimum requirements.

Can I get BREEAM credits for acoustics?

Yes. It is possible to get credits for acoustic performance under Hea 05 and Pol 05. We can provide design stage advice to ensure your development satisfies the relevant criteria and carry out pre-completion testing to verify compliance.

When did sound insulation testing become mandatory?

England and Wales

On 1 July 2003 pre-completion testing became a requirement for rooms for residential purposes and houses and flats formed by material change of use. On 1 July 2004 the requirement was expanded to include new-build developments and in addition, Robust Details became an alternative to sound testing.


On 1 October 2010 post-completion sound insulation testing along with higher performance requirements became a mandatory requirement. However transitional arrangements were made such that testing was only required in new flats from 1 May 2011, and in houses and conversions from 1 October 2011. From January 2012 specific Robust Details that meet the Scottish performance requirements provide an alternative to sound testing.


Part G is currently out for consultation.

Do detached properties need to be tested?

No. Only attached properties are tested.

What is the difference between Rw and DnT,w?

DnT,w is an in-situ measured performance parameter which demonstrates the level of resistance to sound transmission between two adjacent spaces (both direct sound transmission and flanking sound transmission will contribute to the measured performance).

Rw is a performance parameter that describes the level of sound transmitted through a single element, such as a wall, floor, door or window and it is measured in a laboratory where flanking sound transmission is negligible.

The DnT,w of a separating wall or floor will typically be of the order 5 to 7 dB lower than the specified Rw for the single element, due principally to the contribution from flanking sound transmission around the element when it is built on site.

What are Robust Details?

Robust Details are specific design details approved by Robust Details Ltd (RDL) for use as separating walls and floors and have been tested to show their sound insulation performance. They can therefore be used as an alternative to pre-completion testing.

The specific details in the RDL handbook must be followed explicitly and each plot formally 'registered' with RDL. RDL carries out visual inspections and spot check tests before completion of registered plots to check that the plot(s) meet the requirements of the scheme. Robust Details cannot be used in developments formed by a material change of use (e.g. conversions) and so pre-completion testing must be undertaken.

As the specific details in the Robust Details scheme may not allow for flexibility in the design of a development or may not prove cost effective, pre-completion testing may prove a more suitable and effective route to demonstrate compliance.

How much testing is needed?

England and Wales

Approved Document E 2003 states that one set of tests is required for every 10 units in a group or sub-group. A group or sub-group is defined where significant differences in construction or layout occur.

  • Houses - a set of tests would usually comprise two airborne sound insulation tests of a separating wall
  • Flats - a set of tests would usually comprise: two airborne sound insulation tests on the separating wall; two airborne sound insulation tests of a separating floor; two impact sound transmission tests of a separating floor
  • Rooms for Residential Purposes (student accommodation, hotel rooms, care homes etc) - a set of tests would usually comprise: one airborne sound insulation tests of a separating wall; one airborne sound insulation test of a separating floor; one impact sound transmission test of a separating floor.


The sampling rate for testing depends upon the type of dwelling and the form of construction adopted.

Northern Ireland

Either use 'Acceptable constructions' or 'Acceptable upgrading' methods as detailed in Part G, or submit test evidence of construction performance in line with the 'Similar Construction Method' option. Requirements involve obtaining a sample 'set': the mean of the result set must achieve a specific level of performance and each individual result within the set must achieve a different specific level of performance.

How are plots selected for testing?

The building control officer, warranty provider or other concerned parties may require you to carry out tests in specific areas or plots. However where this has not been stipulated we can advise accordingly. Where this is determined in advance of the testing, it should ideally be checked with the concerned party. Tests are usually conducted between pairs of rooms, so adjacent plots will be required.


How is a sound insulation test carried out?

Airborne sound insulation test

A controlled noise is generated by an amplifier and loudspeaker across a broad range of frequencies on one side of a separating wall or floor and the noise level is measured in decibels (dB) using a sound level meter. Measurements are also made on the opposite side of the separating wall/floor (i.e. in the neighbouring dwelling) in order to determine how much of the controlled noise being generated in the source room is transmitted through to the receiving room.

Impact sound transmission test

A calibrated tapping machine which comprises 5 metal 'hammers' driven up and down by a cam and electric motor, is used to simulate footfall noise on the floor surface. The resulting noise is measured in the neighbouring dwelling below, using a sound level meter.

What is reverberation time?

For both airborne and impact tests, the reverberation time (the time taken for sound to decay) is measured in the receive room and forms part of the calculation of the sound insulation performance.

Preparation, timing and testing

Will sound insulation testing disrupt work on site?

During the test, high levels of noise are generated but in order to make accurate test measurements, relatively quiet conditions are needed. Anyone working in the testing area will have to leave temporarily and any noisy works in the vicinity of the test rooms will need to be halted.

The time taken for testing varies with site conditions, but generally a set of tests on houses takes about one hour and a set of tests on flats between two to three hours. During the test we will need free uninterrupted access to the rooms in both properties.

How do I know if I'm ready for a test?

Plots should be at least at second fix stage - for further details please refer to our checklist.

Testing readiness checklist

Sound insulation testing in occupied properties following noise complaints from residents can be carried out at any time when suitable access can be arranged.

Do I need doors and windows on?

Yes, all internal and external doors must be fitted and operable.

What if I only have 110 volt on site?

We can still undertake testing but please make sure you let us know in advance so that we can ensure the correct equipment is brought to site.

Do I have to inform my neighbours of the testing?

If the building is attached in any way to occupied properties then it would be advisable to inform the residents as they are likely to hear the test due to high noise levels generated. In some instances tests may be required that include neighbouring properties. We recommend you check this with Building Control and request access to the neighbouring properties accordingly.

Can I get some peace of mind that I'll pass, prior to testing?

If you would like us to review your designs/proposals and comment on their suitability, please speak to us about our acoustic design advice service.

Can I observe the sound test?

We'll happily give you a brief overview of the test and demonstrate what we do, however, during the formal test(s) there are stringent rules governing the presence of personnel within various rooms so you will need to leave our engineer to it.

Results and failures

Can you email the report to me?

Yes, the completed and signed report will be emailed to you. Printed copies are available if required.

Can you send the report straight to Building Control?

Yes, we do by default where you use NHBC Building Control, to save you time (unless you choose to opt out of this at order stage). We can send them to other Building Control bodies and other parties such as your Code Assessor as long as the details are provided at the time of booking in the testing work.

What happens if a test fails?

In line with the regulations you are required to carry out remedial works to ensure the development meets the relevant performance requirements and re-test. If you don't know what to do by way of remedial works then we can advise you.

You may also be asked by Building Control to test further examples of the construction elsewhere on the development in order to restore confidence and/or highlight the extent of the issue.

Can anyone with the right equipment do the tests?

Approved Document E states that the testing body should preferably be UKAS accredited, or a member of the ANC (Acoustic Noise Consultants) and have joined their PCT registration scheme.

BSRIA is UKAS accredited to undertake sound insulation testing and as such we produce the necessary certificates ourselves rather than relying on a third party to provide the certificates.

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