An example of external plant to be tested for BS4142

Noise Assessments for External Plant; BS4142:2014

It is common within the planning process to be asked for a noise survey to be carried out to assess the noise impact of proposed external plant.

What is meant by External Plant?

Examples of External Plant Include:

  • Air Handling Unit Air Source Heat Pump
  • External Vents and ducting External Vents and Air Handling Unit

The British standard that dominates the planning requirements is BS4142:2014

What is BS4142?

BS4142:2014 has significantly changed the acoustic consultants approach to commercial and industrial noise from the previous version BS4142:1997. The fundamental change is that BS4142:1997 was a numerical demonstration of the likelihood of adverse noise impact, however, BS4142:2014 allows the acoustic consultant to demonstrate knowledge and experience by combining the numerical demonstration with uncertainty and the context of the individual situation.

The context allows the acoustic consultant to demonstrate, that in certain cases, the numerical results calculated do not always provide a true representation of the of the noise environment in question.

BS4142:2014 Method for Rating and Assessing Industrial and Commercial Sound

The significance of sound of an industrial and/or commercial nature depends upon both the margin by which the rating level of the specific sound source exceeds the background level and the context in which it occurs.

  1. Typically, the greater this difference between rating level and background level, the greater the magnitude of the impact.
  2. A difference of around +10dB or more is likely to be an indication of significant adverse impact, depending on context.
  3. A difference of around +5dB is likely to be an indication of an adverse impact, depending on context.
  4. The lower the rating level is relative to the measured background sound level, the less likely it is that the specific sound source will have an adverse impact or significant impact. Where the rating level does not exceed the background sound level, this is an indication of the specific sound source having a low impact, depending on context.


– LA90,T (Background Level) ‘A-weighted sound pressure level that is exceeded by the residual sound at the assessment location for 90% of a given time interval, T, measured using time weighting F and quoted to the nearest whole number of decibels’

– LAR,T (Rating Level) ‘the A-weighted sound pressure level of an industrial noise during a specified time period, adjusted for tonal characteristics and impulsiveness.

As members of the Institute of Acoustics, Limited carry out BS4142:2014 Noise Assessments and Surveys nationally across the UK from our offices based in Liverpool, Tamworth and London. Should you have a requirement for a survey, please do not hesitate to contact us.

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