Useful FAQ's

The following FAQs have been divided up into subject areas to make them easier to locate, including a section called General Interest which, while not directly related to what we do, we felt was interesting nonetheless.

If you have any further queries, please see our Contact page.

What are the basic requirements of the Building Regulations Approved Document E?

ADE applies between separating (party) walls and floors, including onto common areas and is normally subject to testing. Sometimes it is technically not possible to test certain areas due to their being too small (bathrooms and corridors are common examples).


Type of Accommodation Nature of the Building Work Transmission Path Type of Party Element Performance Criterion (dB)
Dwellings Purpose Built Airborne Wall 45 DnTw+Ctr
Floor 45 DnTw+Ctr
Stairs 45 DnTw+Ctr
Impact Floor 62 L'nTw
Formed by Material Change of Use Airborne Wall 43 DnTw+Ctr
Floor 43 DnTw+Ctr
Stairs 43 DnTw+Ctr
Impact Floor 64 L'nTw
Rooms for Residential Purposes Purpose Built Airborne Wall 43 DnTw+Ctr
Floor 45 DnTw+Ctr
Stairs 45 DnTw+Ctr
Impact Floor 62 L'nTw
Formed by Material Change of Use Airborne Wall 43 DnTw+Ctr
Floor 43 DnTw+Ctr
Stairs 43 DnTw+Ctr
Impact Floor 64 L'nTw


ADE also includes criteria for sound insulation between rooms within a unit. Essentially walls and floors should have a proven sound insulation performance of 40 dB Rw. This is not subject to pre-completion testing. Note that this requirement does not apply to:-

Doors onto common areas - these should either have a proven sound insulation performance of 29 dB Rw or an area density of 25 kg/m2.

Walls with doors in them - for instance walls with doors onto corridors are not subject to testing.

Requirement E3 of the ADE states that the common internal parts of buildings which contain flats shall be designed and constructed in such a way as to prevent more reverberation around the common parts than is reasonable. There is no absolute numerical standard. There are two methods described in order to show compliance, namely Method A and Method B.

What are Rw, DnTw, L'nTw and Ctr?

These are all measures of sound insulation, described below in non-technical terms

Rw is essentially the sound insulation of 1 m2 of a material, adjusted for the acoustic properties of the test rooms. The sound insulation of a material varies across the frequency range so the Rw value is frequency weighted to express this varying insulation as a single number. It tends to be a laboratory value and should be used with great caution when considering its application to real life projects.

DnTw is an on-site measurement of sound insulation performance. It is standardised to an assumed reverberation time (eg. 0.5 s for domestic rooms) and is frequency weighted to express the varying performance across the frequency range as a single number.  As it is a sound insultation level, the higher the value, the better the performance (contrast with L’nTw below).

Ctr is an adjustment originally derived from traffic noise measurements, but most commonly found in sound insulation testing. It is a negative number, often ranging between -5 and -15 and provides an adjustment for low frequency content. For instance, a sound insulation of 54 dB DnTw and a Ctr of -9 would give an over performance of 45 dB DnTw+ Ctr and would meet Building Regulations Part E criteria.

L’nTw is used to express the impact sound level, usually measured in the room below a room with a tapping machine. Note that it is a sound level, not an insulation level. Therefore, the lower the value, the better the performance (contrast with DnTw above).

What is speech privacy?

This is the decree to which conversations on one side of a wall or floor can be heard or understood on the other side. It not only depends on the sound insulation of the wall or floor and the loudness of the speech, but also on the background noise level on the "listening" side.

Do I need sound testing for Building Regulations?

Site testing is required under Part E for residential developments (new and change of use). It is required for residential separating (party) walls and floors, but not for internal walls and floors.

Always check with Building Control which walls and floors and floors require testing but a rule of thumb is that 10% of units of a given construction require testing.

Robust details are an alternative route. If a site formally signs up to Robust Details they can avoid testing by using a set of design details which can be expected to pass the Part E requirements with a significant safety margin. The disadvantage is that they are inevitably a slight over-specification and deviating from them in any way will mean that testing is still required.

Do I need air testing for Building Regulations?

Site testing is required under Part L for new residential dwellings. As a very basic rule of thumb, you will need to test 50% of each type of unit but this can vary dramatically. Building Control will define how many units need testing and often which ones.

Do environmental noise surveys need to attended?

Opinions differ on this, but we generally recommend manned surveys wherever possible, unless we are very confident about what the sources are and that they will not change in our absence. Certain types of survey do lend themselves to unmanned surveys, such as long term monitoring, for instance wind farm applications where the noise could vary over a long period of time. Personal observations are often as important as the measurements.

What are the limits for environmental noise? Is there a legal limit for noise?

There is no legal limit. Even guidance is very varied depending on the situation. There are broadly two types of criterion, namely absolute and relative.

Absolute criteria are fixed noise level values. Very common examples are found in BS 8233 which sets design guidance for buildings of various types, such as 30 dB LAeq inside bedrooms at night represents "desirable" conditions

Relative criteria are noise levels relative to the background noise (the noise levels with the noise source in question suppressed). BS 4142 is an industrial standard which rates the likelihood of complaints by comparing the industrial noise with the background noise.

Many standards also recommend special attention being given to certain features of the noise, such as impulsiveness, intermittency, tones, etc. Music noise particularly is widely debated with some arguing for inaudibility as the appropriate criterion, but many arguing that some audibility is acceptable. As with all situations the appropriate standard depends on the environment in question - what might be acceptable in a vibrant part of the city centre might not be acceptable in quiet suburb.

How do I take action against a noisy neighbour?

Residential neighbour noise will often be music, barking dogs, raised voices, TVs, alarms, etc. We will always recommend that people try and talk to neighbours before taking any action. But if that fails or if contact is undesirable for other reasons, then the local authority will normally investigate all noise complaints via the Environmental Health department (often called Environmental Protection, Pollution Control, Housing and Environment or similar).

Industrial, entertainment and commercial neighbours will normally want to take reasonable steps to control unacceptable noise. Again direct contact is normally best but Environmental Health will help if necessary.

The nearby noisy factory (or other commercial premises) was there long before our house was built. What can I do?

Who was there first will not normally make any difference, and generally the party creating the alleged nuisance will have to resolve it.  However, context is a crucial part most assessments and it may be argued that some industrial or commercial noise is part of the general environment and would ned to be considered on a case-by-case basis.

Do I need a noise survey?

If it is likely that employees might be exposed to the various Action Values of the Control of Noise at Work Regulations then it is likely that you will require an assessment. However, since the new regulations came into force, the HSE has been keen  to encourage exposure reduction rather than assessment for assessment's sake. But it is difficult to know where to target nose control without it being properly assessed. Exposure is based on the level of the noise and duration for which a worker is exposed to it.  See our page on Noise at Work.

What are the main criteria under the Control of Noise at Work Regulations?

he regulations identify two Action Values and one Limit Value:

Lower Action Value

  • A daily or weekly exposure likely to exceed 80 dB LEX,8h
  • A peak sound pressure level of 135 dB

Upper Action Value

  • A daily or weekly exposure likely to exceed 85 dB LEX,8h
  • A peak sound pressure level of 137 dB

Exposure Limit Value

  • A daily or weekly exposure likely to exceed 87 dB LEX,8h
  • A peak sound pressure level of 140 dB

The exposure values are based upon how loud the noise is, and for how long an employee is exposed to it, including the effect of working in different areas, with different noise levels, for different lengths of time. The overall daily or weekly exposure value is therefore a single-figure representation of an employee's varying exposure.

What are the Duties under the Control of Noise at Work Regulations?

The regulations require the employer to take certain basic steps where an employee is likely to be exposed above the Lower Action Value, and further steps where an employee is likely to be exposed above the Upper Action Value. An employee must not be exposed above the Exposure Limit Value. Main duties are as follows:-


Action Required

Action Value

Action Value

Action Value

Limit Value

General duty to reduce risk, eg good practice in noise control.


Provide hearing protection for those who ask for it 

  X X X

Hearing protection to be mandatory

    X X

Reduction of exposure (usually noise control)

    X X

Provide information and training about the risks, etc

  X X X

Shall not expose (criminal offense to do so)


What is Acoustic Shock

Acoustic shock is relatively new and little understood phenomenon caused by sudden very loud noises such as in call centre headsets. It can lead to hearing damage and/or tinnitus (ringing in the ears) as well as a wide range of physiological or psychological effects. Its causes and effects are quite different from conventional hearing loss (see the FAQ on Acoustic Trauma) and it needs to be assessed in an entirely different way. See our pages on Acoustic Shock and  Expert Witnessing.

What qualifications/experience do you need to be an expert witness?

Formal qualifications are likely to be expected and considerable experience in a wide range of aspects of noise control and acoustics is absolutely essential. All of ADC's expert witnesses have these in spades. But where many expert witnesses go wrong is in taking it upon themselves to be advocates, often succumbing to pressure from their client or legal advisers. This nearly always gets them unstuck as a case progresses ultimately to cross examination. ADC's expert witnesses are proud of their reputations for consistency (having represented clients from both sides of the various forums (eg. applicants and local authorities, claimants and defendants, as well as single joint exerts). It is vital to provide thoroughly prepared, measured advice and to prepare evidence which can stand up to scrutiny without being blatantly partisan.

Please see our Expert Witnessing page and our services to the Legal Professions page.

What is the loudest noise in nature?

Opinions will inevitably vary on this but to the best of our knowledge, these are the loudest which have in some way been recorded or estimated.

Krakatoa erupted in 1883 and has been estimated to have produced 180 dB. This is a staggering 10,000 times as much sound power as the threshold of pain to humans. It was said to have been clearly audible in Perth nearly 2000 miles away.

However Krakatoa is a pin drop compared to the Tunguska Meteor which is believed to be the loudest event in earth's history . This exploded above Russia in 1908 and is estimated to have created over 300 dB.

The loudest single animal is also the largest, the blue whale, weighing in at 188 dB. However, fans of QI will know that the animal kingdom's record goes to shrimps. What is known as the shrimp layer comprises trillions of shrimps snapping their claws together in unison, creating 246 dB.

How much noise did the Big Bang make?

It was completely silent.

Firstly, for something to be called a noise or a sound it must be a vibration in a fluid (liquid or gas). Of course, there was no such fluid outside of the potential source of noise. There was nothing.

Secondly, for something to be called a noise or a sound it must be in some way possible to witness or measure it. For this you would have to be outside the big bang to do so.

Finally, let us suppose that there was air outside of the big bang when it occurred, and that somehow we could position ourselves outside it to witness the event. The force of the explosion would reach us before the sound.

Is it true that ducks' quacks don't echo?

No it's not!

An echo is simply caused by a sound bouncing off a reflective surface and being heard after the original sound as a discrete event. There is nothing special about a duck's quack that would miraculously stop this basic process from happening. In fact the story was researched by the University of Salford and this finally put the myth to bed.

If anybody knows how the myth became established in the first place we would like to know.

Why/how did the ancient amphitheatres have such good acoustics?

In fact they weren't as great as people think. It is certainly at least an exaggeration that a normal speaking voice can be heard all around the theatres. Tour guides will clap and shout as a way of demonstrating the wonderful acoustics but it really shows nothing spectacular. They had hard surfaces which will have helped to reinforce the speakers' voices but the main advantage they had was very low background noise levels compared to today.