What Is BS4142?

BS4142 is a British Standard that describes the procedures and methods for measuring and assessing noise to determine if it will cause noise complaints at residential properties. BS4142 can be used to assess the potential impact of noise from commercial or industrial noise sources affecting residential properties. BS4142 assessments are commonly requested by Local Planning Authorities.

Most local planning departments will ask for a BS4142 noise survey to be carried out when any noise making activity, or equipment, is going to be introduced close to where people live. A BS4142 noise assessment can be required in order to install air conditioning units, ventilation equipment, water pumps and any other type of mechanical plant which may give rise to noise complaints.

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To carry out a BS4142 assessment, the background noise level (LA90) at the position of the affected residential properties in the absence of the industrial or commercial noise is measured. The background noise level is defined as the noise level exceeded for 90% of a given time period.

The background noise level represents the underlying noise environment at the site in the absence of short-term and atypical noise events.

Having established the background noise level at the position of the residential properties, the average noise level (LAeq) can be measured or predicted from the new commercial or industrial noise source under investigation at the same positions.

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The likely impact of the commercial or industrial noise on the residential properties can then be assessed by comparing the predicted or measured commercial or industrial noise level with the background noise level at each residential position. BS4142 states that, for commercial or industrial noise with no distinguishable features:

  • The louder the commercial/industrial noise is compared to the background noise level, the greater the magnitude of the impact
  • If the commercial/industrial noise is 10 dB or more higher than the background noise level then this is an indication of a significant adverse impact (i.e. this is not normally acceptable)
  • If the commercial/industrial noise is around 5 dB higher than the background noise level then this is an indication of an adverse impact (i.e. this should be avoided if possible)
  • If the commercial/industrial noise is lower than the background noise level, this is an indication of a low impact (i.e. this is normally acceptable). The lower the commercial noise level is, the lower the likely impact.

BS4142 also provides corrections that should be applied to the predicted or measured commercial/industrial noise levels where the commercial/industrial noise contains characteristics that make the noise more intrusive. These characteristics include tonality, impulsivity, and intermittency. The corrections can be significant, meaning that noise containing these characteristics may be severely penalised. The corrections are summarised below.

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Importantly, more than one correction may apply. For example, if a noise is both highly tonal and impulsive then a correction of +15 dB may be applicable. In this case, even if the commercial/industrial noise level was equal to the background noise level, the BS4142 rating would be +15 dB above background, and therefore deemed to result in a “significant adverse impact”.

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