It should be noted that although this is the Environmental Noise section of the NoiseNet, much of what follows is also applicable to internal noise, such as mechanical services and air conditioning plant.
The World Health Organisation recommendations of 1980 "Environmental Health Criteria 12: Noise" have been used as the basis for many assessment criteria in the UK; for example the nighttime recommendations of both PPG24 and the DTI ETSU wind farm assessment methodology are both partly based on the 1980 WHO criteria. At section 188.8.131.52 of the 1980 WHO Criteria it is stated-
With regard to external daytime noise, in order to avoid the possibility of community annoyance, a limit (presumably free field) of 55 LAeq,T is recommended.
The WHO Guidelines for Community Noise were revised in 1999 and the latest version can be read elsewhere; in brief it recommends a nighttime Leq of 30 dBA and that in general peaks of 45 dBAF or more should be avoided. As regards daytime noise the recommended limit is lowered to 50 LAeq,T.
BS 8233:1999 "Sound insulation and noise reduction for buildings - Code of Practice", amongst many other matters, has incorporated the above WHO guidance (old and new) into its section 7.6. Anonymous noise, such as that from road traffic, mechanical services or continuously running plant, is considered in Tables 5 and 6. An extract of Table 5 appears below
A footnote to this table states that "For a reasonable standard in bedrooms at night, individual noise events (measured with F time-weighting) should not normally exceed 45 dB LAmax".
With regard to the time period to be used for the assessments BS.8233:1999 states at 7.3 "Unless otherwise stated, the noise should be assumed to be steady, such as that due to road traffic... The time period T should be appropriate for the activity involved (e.g. 23.00-07.00 for bedrooms)." Therefore the time periods for the noise limits are based on 8 hours for nighttime (bedrooms) and 16 hours for daytime (living rooms).
At Section 184.108.40.206 of the British Standard, gardens are considered "As well as protection for the building. Barriers or bunds should be considered to protect the gardens. In gardens and balconies etc. it is desirable that the steady noise level does not exceed 50 LAeq,T dB and 55 LAeq,T dB should be regarded as the upper limits." On a similar basis to the above, it is considered that the time period should probably be 16 hours because we are dealing with daytime noise.
With regard to nighttime noise, there has also been a UK High Court case considering nighttime noise from industrial premises "Murdoch & an v Glacier Metal Co. Ltd" (CA Gazette 18-Feb-1998). Here noise from a nearby factory, was above the then World Health Organisation recommended level (35 LAeq); the Court determined that it was not an actionable nuisance; the Court decided that allowance should be made for the character of the neighbourhood, i.e. the fact that nighttime levels exceed the WHO 1980 levels does not automatically mean that noise levels are a nuisance.