BS 4142 or BS 8233: which noise standard applies
BS 4142 assesses industrial and commercial sound affecting existing dwellings. BS 8233 sets internal ambient targets for the building you are creating. Here is which one a council asks for, and when both apply.
If the noise comes from your plant and affects somebody else's home, the assessment is BS 4142. If the noise comes from outside and affects people inside a building you are creating or converting, the assessment is BS 8233. That is the whole of the BS 4142 vs BS 8233 question, and almost every argument about it comes from applying one method to the other's job.
The two standards measure different things, use different descriptors and produce different kinds of answer. One produces a judgement about impact on existing neighbours. The other produces a target that your building has to achieve.
The question each standard answers
BS 4142:2014+A1:2019 covers methods for rating and assessing sound of an industrial and commercial nature. Its subject is the sound your kitchen extract fan, your condenser units, your refrigeration plant or your loading activity makes at a nearby residential window. It compares that sound against the existing background and expresses the result as a likelihood of adverse impact.
BS 8233:2014 is guidance on sound insulation and noise reduction for buildings. Its subject is the acoustic environment inside rooms, and it gives internal ambient target levels for dwellings along with external amenity guidance for gardens and balconies. It says nothing useful about whether your plant will annoy the neighbours.
| BS 4142:2014+A1:2019 | BS 8233:2014 | |
|---|---|---|
| Source assessed | Industrial and commercial sound | Ambient noise, usually road, rail or aircraft |
| Receptor | Existing dwellings outside the site | Occupants of the proposed or converted building |
| Main descriptor | Rating level against background LA90 | LAeq inside rooms, with LAmax at night |
| Output | Likelihood of adverse impact | Pass or fail against a target level |
| Typical application | Plant, extraction, deliveries, machinery | New flats, office to residential conversion |
The rating level and its corrections
BS 4142 works on a difference. The specific sound level of the source is measured or predicted at the assessment position, corrections are added for the character of the sound, and the resulting rating level is compared with the background sound level, measured as LA90 over the relevant period.
The character corrections are where assessments diverge, because they involve judgement. Tonality, for example a fan blade frequency or a compressor whine. Impulsivity, such as a bin lid or a reversing beeper. Intermittency, where the source switches on and off in a way that attracts attention. A further correction is available for other distinguishing features.
The standard's own guidance on the outcome is a sliding scale rather than a limit. A rating level around 10 dB or more above background indicates a significant adverse impact is likely. Around 5 dB above suggests an adverse impact. A rating level at or below background is an indication of low impact. All of it is then read in context, which includes the absolute level and the character of the area.
Two consequences matter commercially. A quiet residential street gives you a low background and therefore a hard target, so the same air conditioning unit can pass in one location and fail 400 metres away. And acoustic consultants earn their fee at the correction stage, because a 3 dB tonal correction can decide the application.
Internal guideline values and how a scheme meets them
BS 8233 sets indoor ambient targets for resting and sleeping, expressed for living rooms and bedrooms over the daytime and night-time periods, with separate guidance on maximum night-time events and on external amenity areas. The figures are design targets rather than statutory limits, and the Professional Practice Guidance on Planning and Noise, published jointly by the acoustics institutes, sets out how they should be used alongside the Noise Policy Statement for England's observed effect levels.
Meeting them is a glazing, ventilation and layout exercise. The chain runs: measured external facade level, glazing and frame specification, ventilator type and its attenuation, then the internal level achieved with the ventilation path open.
That last clause is where schemes fail. An acoustic case that only works with the windows shut collides with overheating, because the simplest cooling strategy is an openable window. The two assessments have to be run together, which is the practical reason the choice between TM59 modelling and the Part O simplified method is worth settling early, and why the Overheating Risk Assessment and the acoustic strategy should be written by people who have spoken to each other.
Which standard a council cites for plant noise
Environmental health officers consulting on a restaurant, gym, takeaway or small industrial unit ask for BS 4142. Expect a request for a background sound survey covering the proposed hours of operation, including the quietest period you intend to run plant.
The usual local policy requirement is that the rating level should not exceed the background level, or should sit a stated number of decibels below it. Five dB below background is a common local formulation, and some authorities use 10 dB below for night-time operation. Those are local policy positions rather than anything in the standard itself, so read the adopted local plan policy and any noise guidance note before designing the plant enclosure.
The assessment belongs in a Noise Impact Assessment, and councils expect a suitably qualified acoustician as the author. Where the application also involves cooking extract, the odour and noise cases are usually presented together with the Ventilation and Extraction Statement, because the fan that solves one problem creates the other. A draft of either should be reviewed by that professional before it goes in.
Where both apply to the same application
Mixed use schemes need both, and so do conversions above existing commercial premises. A ground-floor cafe with flats above produces a BS 4142 case for the cafe's plant affecting the new flats and the existing neighbours, and a BS 8233 case for road traffic noise reaching those flats.
Internal noise transfer between the commercial unit and the dwellings above is a third question again, dealt with through sound insulation design and Building Regulations Approved Document E rather than through either planning standard. Keep the three separate in the report, with a short paragraph saying which method answers which question. Officers read that paragraph with relief.
Survey design differs for each method
| Element | BS 4142 survey | BS 8233 survey |
|---|---|---|
| Position | At or near the affected dwelling's facade | At the proposed facade, floor by floor if needed |
| Period | Covering proposed operating hours, including the quietest | Representative daytime and night-time periods |
| Descriptor recorded | LA90 background, plus specific sound level | LAeq and LAmax, with spectral data |
| Weather | Recorded, with wind speed and direction logged | Recorded, same requirement |
| Duration | Long enough to establish a reliable background | Long enough to capture typical traffic variation |
Avoid school holidays for either, because traffic and activity patterns shift. Note the weather honestly: a survey carried out during an unusually wet week will have an unrepresentative background, and a consultee will spot it.
Conditions that fix a noise limit
A permission granted on a BS 4142 case usually carries a condition expressing the plant limit, and the wording decides how much trouble it causes you later. A condition tying the rating level to a specified number of decibels below the measured background at a named assessment position is testable. A condition requiring that plant shall cause no nuisance is not, and invites argument.
Watch for three things. A requirement for post-installation verification by measurement, which means commissioning the plant to the design assumptions. A restriction on hours of operation that may be tighter than your trading hours. And a limit expressed at a position you cannot access, which makes compliance testing dependent on a neighbour's cooperation. The difference between a condition and an advisory note on the decision matters here, as set out in our note on a planning condition or an informative.
Get the background survey done before the plant is specified, not after. Enter your postcode on PlanScope to see which reports a change of use is likely to need.
This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
Which standard applies to an air conditioning unit on a shop roof?
BS 4142:2014+A1:2019, because the unit is commercial plant affecting existing residential receptors. The assessment predicts the rating level at the nearest affected window, adds character corrections for tonality or intermittency, and compares the result with the measured background sound level. BS 8233 has no role unless the application also creates dwellings of its own.
What internal noise levels does BS 8233 expect?
It gives indoor ambient guideline values for living rooms and bedrooms across daytime and night-time periods, with separate guidance on maximum night-time events and on external amenity areas such as gardens. They are design targets, not statutory limits, and are normally applied alongside the Professional Practice Guidance on Planning and Noise and the Noise Policy Statement for England.
Can a rating level above background still be acceptable?
Yes. BS 4142 presents the difference as an indication rather than a pass or fail line, and requires the result to be read in context, including the absolute level and the character of the area. Local plan policy often sets a tighter local test, such as a stated number of decibels below background, so check the adopted policy wording.
Why does an acoustic report conflict with the overheating assessment?
Because the standard acoustic fix is to keep windows closed and ventilate mechanically, while the standard overheating fix is to open windows. Running both assessments on the same ventilation assumption resolves it. Where closed windows are needed for noise, the cooling strategy has to deliver without them, which affects both cost and the energy strategy.
Who should write the noise assessment?
An acoustician with experience of the relevant method, usually a member of the Institute of Acoustics. Both standards involve judgement calls, on character corrections in BS 4142 and on survey representativeness in BS 8233, that a consultee will test. Any draft should be reviewed and signed off by that professional before the application is submitted.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.