BS8233: 2014: ‘Guidance on sound insulation and noise reduction for buildings’ provides guidance on indoor ambient noise levels for dwellings which are applicable in this case and which are set out in Table 4 of the document.  These are set out below.

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A note to this table states:

 

NOTE 7  Where development is considered necessary or desirable, despite external noise levels above WHO guidelines, the internal target levels may be relaxed by up to 5 dB and reasonable internal conditions still achieved.

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Allowing for this relaxation the figures in Table 4 are as set out below:
 

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The 1999 edition of the document also included an internal maximum noise level standard for bedrooms at night, although this does not appear in the current version.  In accordance with World Health Organisation (WHO) guidance (which is still current), the 1999 edition recommended that an internal noise level of 45 dB LAmax should be exceeded no more than approximately 10 to 15 times per night in bedrooms. Allowing for a relaxation of 5 dB for this maximum noise criterion results in an internal noise level of 50 dB LAmax that should be exceeded no more than approximately 10 to 15 times per night in bedrooms.

 

In respect of noise levels in garden areas BS8233: 2014 states:

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“For traditional external areas that are used for amenity space, such as gardens and patios, it is desirable that the external noise level does not exceed 50 dB LAeq,T, with an upper guideline value of 55 dB LAeq,T which would be acceptable in noisier environments.  However, it is also recognized that these guideline values are not achievable in all circumstances where development might be desirable.  In higher noise areas, such as city centres or urban areas adjoining the strategic transport network, a compromise between elevated noise levels and other factors, such as the convenience of living in these locations or making efficient use of land resources to ensure development needs can be met, might be warranted.  In such a situation, development should be designed to achieve the lowest practicable levels in these external amenity spaces, but should not be prohibited.”

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Paragraph 6.2.2 of the document also states that for moderate and heavy traffic flows a 16-hour LAeq noise level can be derived from an 18-hour LA10 level by subtracting 2 dB.  This conversion factor was previously provided in Planning Policy Guidance note 24 ‘Planning and Noise’ (PPG24).