Construction noise assessment under BS 5228

A BS 5228 construction noise assessment answers one question for the case officer: will the works cause a noise impact that needs controlling, and if so, what should the condition say. The method that gets used almost everywhere in England is the ABC approach in Annex E of BS 5228-1, which compares predicted site noise at the nearest receptor against a threshold set by the existing ambient level. Get the ambient measurement wrong and every number downstream is wrong, which is why the baseline survey deserves more attention than the modelling.

The ABC method and where the thresholds come from

The ABC method sorts the receptor into one of three categories based on the existing ambient noise level, rounded to the nearest 5 decibels, then applies a threshold value to the predicted construction noise level.

The values are LAeq over the relevant period at the facade of the receptor. Category A applies where the rounded ambient level is below the category A value, category B where it equals it, and category C where the ambient is higher. So a terraced house on a quiet cul-de-sac is category A with a 65 dB daytime threshold, and the same house on an urban distributor road may be category C with a 75 dB threshold. Exceeding the threshold indicates a potential adverse effect, which triggers the mitigation discussion rather than deciding the application.

Two practical points. The ambient survey should be long enough to characterise the periods you are assessing, which usually means unattended monitoring across at least a weekday and a weekend. And where the receptor has been chosen for convenience rather than exposure, an environmental health officer will ask why, so pick the worst affected facade and justify it.

Predicting levels from plant and activity data

Prediction under BS 5228-1 is arithmetic, and it is checkable, which is the reason to set it out fully. The inputs are the sound power or sound pressure level of each item of plant, the distance to the receptor, the proportion of the period each item is operating, and corrections for screening, ground effects and reflections.

The standard's own annexes give measured levels for common plant and activities, which is where most assessments take their source data. Where you use manufacturer data instead, say so and give the reference conditions.

The assumptions that change the answer are on-time percentages and phasing. An excavator running 100 per cent of an eight hour day at 12 metres from a boundary produces a very different figure from one running 40 per cent at 25 metres. Set out a phase by phase table: demolition, site clearance, piling, substructure, superstructure, external works. Piling and demolition are usually the phases that breach a threshold, and they are also the shortest, which is the argument that supports a time limited condition rather than a permanent restriction.

State the duration of each phase in weeks. A threshold exceedance for three days reads differently from the same exceedance for four months, and BS 5228 expects duration and character to inform the judgement.

Vibration prediction and human response

Vibration is assessed under BS 5228-2 and is a separate exercise from noise, with its own source data for piling, vibratory rolling, breaking and vehicle movements. Predictions are usually expressed as peak particle velocity in millimetres per second at the receptor, using the empirical relationships in the standard, then compared against guide values for human response and for building damage.

Human response comes first, because people complain long before anything is damaged. The standard's guidance describes vibration around 0.3 millimetres per second peak particle velocity as distinctly perceptible in residential environments and around 1 millimetre per second as likely to cause complaint. Cosmetic damage guide values for residential property are an order of magnitude higher, with transient vibration guide values of 15 millimetres per second at 4 hertz rising to 20 millimetres per second at 15 hertz and above.

The gap between those two sets of numbers is the whole practical problem. A piling operation can be comfortably below any damage threshold and still generate a stream of complaints and a demand for a structural survey from every neighbour within 50 metres. Where the works are close to sensitive or historic fabric, a pre-condition survey of the adjoining properties is worth every penny, and the detail belongs in your construction vibration assessment.

Best practicable means in practice

Best practicable means is a statutory concept from section 72 of the Control of Pollution Act 1974, and it is what a council will hold a contractor to whether or not the phrase appears in the condition. It takes account of local circumstances, the current state of technical knowledge, and the financial implications.

In a BS 5228 assessment it should read as a specification, not as a list of aspirations. Useful mitigation commitments include the plant selection itself, such as choosing an auger bored piling technique over driven piling where ground conditions allow, acoustic screening at a stated height and mass along the affected boundary, locating fixed plant and compounds at the far side of the site, restricting the hours of the noisiest activities to a narrower window than the general working hours, and using electric rather than diesel plant where a supply exists.

Broken out that way, each item can be secured. A commitment to use hoardings of a stated surface mass is enforceable. A commitment to minimise noise is not, and a contractor who inherits the second will do less than one who inherits the first.

Monitoring, trigger levels and reporting

Monitoring is worth proposing rather than waiting to have imposed. It gives the contractor evidence when a complaint arrives and it gives the environmental health officer confidence to accept a less restrictive condition.

A workable regime has four parts. Fixed monitoring positions at the two or three most exposed receptors, stated as coordinates or on a plan. Trigger levels set a few decibels below the assessment threshold, so there is time to react. A defined response when a trigger is breached, naming who investigates and within what period. And a reporting frequency, usually weekly during the noisiest phases and monthly thereafter, sent to the council.

Set trigger levels honestly. A trigger set at the threshold itself produces breaches with no time to act, and a trigger set 15 decibels below produces so many alerts that everyone stops reading the reports.

Handling complaints on site

The complaints procedure is part of the assessment for a reason. Most enforcement problems on construction sites start with a resident who could not find anyone to speak to.

Commit to a named site contact with a telephone number displayed at the entrance and on a letter to the surrounding streets before works start, a log of every complaint with the time, the activity underway and the response, and a notification letter ahead of the noisiest phases with dates. Piling notified two weeks in advance generates a fraction of the complaints of piling that starts unannounced on a Monday morning.

Where a council has served a notice under section 60 of the Control of Pollution Act 1974, or the contractor has obtained prior consent under section 61, the monitoring and complaint arrangements will usually be written into it. That statutory regime runs alongside planning conditions, and the two can impose different hours, which is a conflict worth resolving before work starts rather than after. A planning condition also cannot cure a statutory nuisance, as set out in statutory nuisance and planning.

Where the assessment lands in the planning documents

On a major application the construction noise assessment usually sits inside the Noise Impact Assessment or as its own chapter, with the mitigation commitments carried across into the Construction Management Plan that the council will condition.

Keep the two consistent. Where the assessment says screening will be 3 metres high along the eastern boundary and the management plan says 2.4 metres, the discrepancy will be found at discharge of conditions stage, and the assessment will have to be redone. Councils usually expect a suitably qualified author for noise work, and professional review is strongly advised before submission.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified acoustician before relying on it, because thresholds, monitoring expectations and hours differ between authorities.

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