BS 4142 or ProPG: choosing the right noise method

Pick the method from the direction of the problem. BS 4142:2014+A1:2019 is for industrial and commercial sound arriving at residential receptors, so it is the method when your scheme makes the noise. ProPG, the Professional Practice Guidance on Planning and Noise for new residential development, is for the opposite case, where you are putting dwellings into an existing noise climate dominated by transport. Choosing the wrong one is the single most common reason an acoustic report comes back from environmental health with a request for more work.

The two documents answer different questions, use different descriptors and produce different outputs. They are not alternatives you can select on preference.

What BS 4142 actually measures

BS 4142 compares a rating level with a background sound level and reports the difference, then interprets that difference in context. The specific sound level is the LAeq,Tr of the source alone over the reference time interval, which is one hour during the day and 15 minutes at night. The background is the LA90,T over the same periods, representative of the quietest conditions the source will be heard against.

The rating level is the specific sound level plus acoustic feature corrections. Tonality, impulsivity, intermittency and other distinguishing characteristics each attract a correction, and the standard sets out how to derive them, including a subjective route and objective methods. A rating level around and above 10 dB over background indicates a significant adverse impact depending on context. Around 5 dB indicates an adverse impact. At or below background the impact is low.

Context is not decoration in this standard. The 2019 amendment made clear that the initial estimate must be modified by the absolute level, the character of the residual sound and the sensitivity of the receptor. An uncritical plus-five-equals-refusal reading will be picked apart.

What ProPG asks you to demonstrate

ProPG runs a two stage process. Stage 1 is an initial site noise risk assessment that places the site in a negligible, low, medium or high risk band using measured or modelled external levels. Stage 2 is the full assessment, and it has four elements: demonstrating good acoustic design, achieving internal noise levels, providing acceptable external amenity space, and dealing with other relevant issues such as ventilation and overheating.

The internal targets come from BS 8233:2014, generally 35 dB LAeq,16hr in living rooms during the day and 30 dB LAeq,8hr in bedrooms at night, with external amenity areas treated as desirable at 50 dB LAeq,T and an upper guideline of 55 dB. ProPG expects you to show the design steps taken before you reach for glazing specifications, because mitigation by layout, orientation and massing is more durable than a window that has to stay shut.

That last point is where ProPG collides with Approved Document O. If your acoustic strategy relies on closed windows and your overheating strategy relies on open ones, the two reports contradict each other and an officer will notice. Resolve it in the design, and keep the overheating risk assessment and the acoustic work in the same conversation.

Source and receptor decide the method

The fourth row is the one people get wrong. If you are building houses next to an operating business, the agent of change principle means your scheme carries the mitigation burden, and the assessment usually needs both methods: BS 4142 to characterise what the existing operator emits, and ProPG to show the dwellings will be acceptable. Presenting only one half invites a holding objection.

Background sound is measured differently in each

For BS 4142 you need the background level at the receptor during the periods the source will operate, including the quiet ones. Measuring a 24 hour survey on a Tuesday and taking a single overall LA90 defeats the purpose, because the night-time background that governs the assessment sits somewhere inside that dataset.

For ProPG the relevant quantity is the ambient level, typically free field LAeq over 16 hours and 8 hours plus LAmax,F for individual events at night, because the assessment is about what the future occupants will experience rather than about a single source standing out.

Practical points that survive scrutiny:

1. Log in short intervals, five or fifteen minutes, so you can re-cut the data later rather than re-measure.
2. Record weather, and discard periods with wind speeds that compromise the microphone.
3. Photograph the position and give coordinates, heights above ground and the distance to the facade.
4. State whether values are free field or facade, and apply the correction consistently.
5. Keep the calibration records. Environmental health officers do ask.

Presenting results so environmental health can agree them

Write the report so a busy officer can find four things in under a minute: the measurement positions, the assumed plant or transport source levels, the comparison against the relevant criterion, and the mitigation that closes any gap. Put the raw time history in an appendix rather than the main text.

Where mitigation is needed, propose the condition wording yourself. A condition expressed as a rating level not exceeding a stated value relative to the measured background at a defined position is enforceable and gives the operator room to select equipment. A condition naming a particular fan model is neither. If a condition later proves unworkable, changing it means a section 73 application rather than a phone call.

Noise Impact Assessments sit in the group councils expect a suitably qualified author to prepare, and professional review is strongly advised before submission. PlanScope drafts the Noise Impact Assessment structure, the policy framing and the method narrative from your project details, then routes it for sign-off through the professional review directory. Measurement and interpretation remain the acoustician's work.

Errors that send a report back

The recurring ones, in the order officers seem to raise them:

• Applying BS 4142 to road traffic noise, which the standard expressly excludes.
• Omitting acoustic feature corrections for a tonal fan or an impulsive process, then reporting a comfortable result.
• Taking background measurements on a day when the dominant existing source was itself unrepresentative, such as during a road closure.
• Assessing only the daytime period when the plant runs overnight.
• Stopping at internal levels under ProPG without addressing external amenity space or ventilation.
• Treating the plus 5 and plus 10 figures as pass and fail lines rather than indicative of impact before context.
• Using a single figure for a site with several distinct receptors at different distances and orientations.

None of these are exotic. They happen because the method was chosen after the measurements rather than before.

Get the direction of travel clear at the first site visit, and the rest of the assessment follows. If you want to see which technical reports a scheme like yours usually needs alongside the acoustic work, enter the postcode on PlanScope and the recommendation engine will list them.

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.