BS 8233 or ProPG? What the council is actually asking for.

A council asks for a BS 8233 assessment, or a ProPG assessment, or a noise assessment "in accordance with BS 8233 and ProPG", and the applicant reasonably wonders whether these are three different reports. For new homes affected by transport noise, all three nearly always mean one report. ProPG is the framework. BS 8233 supplies the internal target values the framework tests against. The useful question is not BS 8233 vs ProPG, but which parts of that one report the council's wording is pointing at.

This note sets out how the two fit together, what each ProPG stage asks for, how night maximum levels are handled, where BS 4142 comes in, what the report must contain, and the misreadings on both sides of the planning desk.

Two documents doing different jobs

BS 8233:2014 is a British Standard giving guidance on sound insulation and noise reduction for buildings of many kinds, not only homes. For planning, its most quoted content is the table of internal ambient noise levels for dwellings: 35 dB LAeq,16hour in living rooms and bedrooms by day, 30 dB LAeq,8hour in bedrooms at night, with guidance on gardens and balconies alongside. It says what a room should achieve. It does not say whether a site is suitable for housing, how the layout should respond, or what the officer should be told to decide. Our BS 8233 explainer sets out the full table and how it turns into a glazing specification.

ProPG: Planning & Noise is professional practice guidance, published in 2017, for new residential development exposed mainly to transport noise. It is not a British Standard and it is not policy. It is a process: assess the risk the site carries, show through four elements that the design responds to it, then make a recommendation. When it reaches internal noise levels, it uses the BS 8233 values. So a ProPG assessment contains a BS 8233 assessment. A BS 8233 assessment on its own is the narrower piece: the internal level calculation, the glazing and ventilation that follow from it, and usually a check of gardens and balconies.

ProPG asks whether the site and the design work. BS 8233 tells it what a room should sound like when they do.

BS 8233 or ProPG: which one the council means

The wording tells you. A validation checklist asking for a noise assessment in accordance with ProPG wants the whole framework, from the risk assessment to an acoustic design statement. A condition requiring internal levels in accordance with BS 8233 before occupation is usually a narrower request: show that the rooms meet the values, specify the glazing and ventilation that get them there, and sometimes verify the result once built. The officer's report and the environmental health consultation response normally say what prompted the request, and are worth reading first.

Where the wording is loose and the source is transport, the ProPG structure is the safer answer. A report that works through ProPG's elements in order also answers a BS 8233 request completely; the reverse is not true. Where the wording is plainly narrow, such as a condition being discharged after the layout has been approved, the report should answer that condition and not reopen design questions the council has already settled.

Stage 1: the initial site noise risk assessment

ProPG starts with the site as it is. The day and night transport noise levels across it, measured or predicted, place it in a risk band: negligible, low, medium or high. The levels are taken without the mitigation the scheme might later add, because the point is to show how much the noise will have to shape the design. Frequent loud events at night count too: a site where high maximum levels recur through the night should not be treated as negligible risk on the strength of a low average.

Two things the risk band is not. It is not a decision: a high-risk band warns that the risk of refusal rises and that a detailed design response will be needed, not that the scheme will be refused. And above negligible it is not the end of the work: low, medium and high all lead into the full assessment and an acoustic design statement, scaled to the risk.

Stage 2: the four elements, and where BS 8233 sits

• Element 1, good acoustic design: evidence that layout, orientation, massing and room arrangement respond to the noise, and that ventilation and overheating were designed alongside the acoustics rather than after them
• Element 2, internal noise levels: the BS 8233 values for living rooms and bedrooms, plus a maximum level check for bedrooms at night. This element, with Element 3, is where the BS 8233 assessment sits
• Element 3, external amenity: gardens, balconies and shared space against the BS 8233 external guidance, with a reasoned case where a compromise is unavoidable
• Element 4, other relevant issues: national and local policy, how far the scheme meets the guidance overall, likely occupants, unintended adverse consequences of the acoustic design, and the wider planning objectives it balances

Element 1 comes first for a reason. Good acoustic design is not glazing. A report that jumps straight to Element 2 has produced a BS 8233 assessment and labelled it ProPG, and the officer's first question will be about the layout, not the glass. Our ProPG explainer covers each element in more depth.

ProPG then closes with a recommendation to the decision maker: grant without noise conditions, grant subject to conditions, or refuse on noise grounds, either to avoid significant adverse effects or to prevent unacceptable ones. The report should say which outcome the evidence supports; the decision is the council's.

Maximum levels at night

An LAeq is an average over the period. A bedroom can meet 30 dB LAeq,8hour and still have a freight train or a passing HGV wake its occupant several times a night. BS 8233 recognises this: where regular individual noise events occur, it notes that a separate guideline value may be needed, set as a maximum level or a sound exposure level. ProPG gives the working expectation. In most circumstances good acoustic design can keep individual events in bedrooms at night from normally exceeding 45 dB LAFmax more than 10 times a night. Where that is not reasonably practicable, acceptability turns on the source, number, distribution, predictability and regularity of the events, not on the maximum level alone.

Three details decide whether this part of an assessment holds up. The index: the criterion is LAFmax, the maximum with fast time weighting, and a slow-weighted maximum can read lower for short events, so the two are not interchangeable. The count: the criterion is about how often, so the report has to state how many events occurred and which one it designed to, rather than quoting only the single loudest or an average of all of them. The survey: the night data has to capture the events that matter, which beside a freight line or a road carrying night-time HGVs means logging right through the night and attributing the peaks. On many bedroom facades it is the maximum level, not the LAeq, that sets the glazing.

When BS 4142 also applies

ProPG is built for transport noise. A commercial or industrial neighbour, such as rooftop plant, a workshop, a service yard or a delivery bay, is assessed under BS 4142:2014+A1:2019, which compares a rating level outside the home with the background sound level. Our BS 4142 explainer sets out how the rating level is built.

The two methods do not merge. BS 4142 is an external comparison: it rates sound outside the home against the background sound level outside, and is not a method for setting indoor levels. So on a site with both a road and a commercial neighbour the report carries two strands: ProPG with BS 8233 for the transport noise, and BS 4142 for the commercial source. The BS 8233 values then apply again to the rooms facing that source, with lower targets considered where it has a specific character, such as tones or strong low-frequency content, since the BS 8233 table covers only noise without one. Folding everything into one LAeq and testing it against BS 8233 alone loses the corrections that make BS 4142 sensitive to tonal and impulsive sound. Music and voices from licensed premises are not what BS 4142 is designed to rate and need their own assessment. Under the agent of change principle, the new homes are expected to carry the mitigation, not the business already there.

What the report has to contain

A full ProPG assessment contains the following. A narrow BS 8233 condition needs the survey, internal levels, specification and conclusion.

• The council's wording quoted at the front, and the standards and guidance the report relies on named
• The survey method to BS 7445: dates, durations, positions, Class 1 instruments with current laboratory calibration certificates, field calibration checks before and after, and the weather
• The Stage 1 risk band, with the day and night levels that put the site there
• The Element 1 narrative: what the layout does about the noise, and what was considered and set aside
• Internal levels room by room, day and night LAeq and night LAFmax, with windows open and closed
• Glazing and ventilation specified in performance terms, coordinated with the overheating strategy where Approved Document O applies
• External amenity results, and the reasoning wherever a compromise is proposed
• A BS 4142 assessment of any commercial or industrial source
• A conclusion and recommendation that follow from the numbers and say what they depend on

Common misreadings by applicants

• Assuming a site is negligible risk from the daytime traffic alone, without measuring the night or looking at maximum levels
• Meeting BS 8233 with the windows shut and stopping there. Closed windows need an alternative ventilation route that is itself assessed for noise, and on a new-build scheme the Approved Document O strategy may depend on opening them at night
• Starting at the glazing schedule and skipping Element 1
• Reading the BS 8233 allowance to relax the internal targets by up to 5 dB, where development is considered necessary or desirable, as a design margin. It is a case for the decision maker to accept, not headroom to design into
• Submitting a ProPG assessment of the road and saying nothing about the plant room next door

Common misreadings by officers

On the officer's side, the misreadings are rarely about acoustics. They are about the status of the numbers.

• Conditioning the BS 8233 values as absolute limits to be met at all times with windows open. The standard presents them as guideline values, and a condition worded that way can be unachievable on a site the officer is otherwise content to approve
• Treating the external amenity guidance as a pass mark for every balcony on a city-centre scheme, where BS 8233 itself accepts that a compromise may be necessary
• Asking for BS 4142 to be applied inside the home, or to road and rail noise, neither of which it is designed for
• Requesting a ProPG risk assessment where the only source is a commercial neighbour. BS 4142 answers that question, though the principles of good acoustic design still apply
• Treating 45 dB LAFmax as a ceiling never to be crossed, when ProPG frames it around how often events occur
• Reading the Stage 1 risk band as the outcome of the application

None of these is a reason to argue with the officer. The answer is a report that states the status of each number plainly, so the condition that follows is one the scheme can meet.

Getting the scope right

Most of the cost of getting this wrong comes from answering the wrong question well. Send us the condition, the checklist entry or the environmental health response with the postcode, and the engineer who will run the survey reads the wording first and quotes a fixed fee for what it actually asks. The report lands within five working days of the survey. Our residential noise assessments page sets out how one runs.