Noise report outline for restaurant plant in a courtyard

A restaurant plant noise report for a courtyard installation has one job that a standard template will not do for you: show what the enclosing walls do to the sound. A free field calculation assumes sound spreading over open ground with nothing to reflect off. A courtyard enclosed on three sides by brick, with flats above, is the opposite of that, and the difference shows up when the council's verification test is carried out after opening.

So write the report in the order below, and put the enclosure into the calculation rather than into a caveat at the end.

Describing the plant and its duty cycle

Start with a schedule, one row per item. Kitchen extract fan. Make-up air supply. Refrigeration condensers, each one listed separately. Cellar cooler. Air conditioning condensers. Any gas booster or pump.

For each item give the make and model, the sound power level in decibels with octave band data where available, the source of that figure, and the mounting arrangement. Say whether the manufacturer's figure is a sound power level or a sound pressure level at a stated distance, because mixing the two is the single most common arithmetic error in these reports.

Then the duty cycle, hour by hour across a 24 hour period. This matters more than most applicants realise. The extract runs during opening hours against a daytime background. Refrigeration cycles all night, against a background that may be 20 dB lower. The night-time case almost always governs, and a report that assesses only the daytime has assessed the easy question.

Give the worst case combination explicitly: which items run simultaneously, at what time, and why that is the worst case.

Survey position and background determination

Choose the assessment position by reference to the nearest noise sensitive window rather than by convenience. In a courtyard scheme that is often a flat directly above or across the yard, sometimes three metres away.

State the position, the microphone height, whether the measurement was free field or facade, and the distance to any reflecting surface. If a facade measurement was taken, say what correction was applied to convert it.

Survey over a period long enough to show a representative pattern, covering the quietest times the plant will operate. Record the weather, note any atypical events, and exclude them with an explanation rather than silently. Then present the background sound level for each relevant reference time interval, daytime and night, with a short justification of the value taken forward.

The lowest representative background is what the assessment turns on. Selecting a background from a busier hour to make the arithmetic work is the thing an environmental health officer will look for first.

Source data and manufacturer figures

Three columns tell the reader whether to trust the rest of the report: the quantity, its value, and where it came from.

Use manufacturer data sheets and append them. Where a figure is quoted at 1 m or 3 m, show the conversion to sound power. Where octave band data is available, use it, because the attenuation you later propose will perform differently at different frequencies and a single figure calculation cannot show that.

Derate where the installation differs from the test condition. A condenser mounted hard against a wall, or on a bracket rather than a plinth, or with restricted airflow forcing the fan to a higher speed, will not perform as the sheet says. State the allowance and the reason.

Propagation and courtyard reflections

This is the section that distinguishes a real assessment from a spreadsheet.

Sound from plant in an enclosed courtyard reaches the receptor by a direct path and by multiple reflected paths off the enclosing walls, and those reflections raise the level above the open ground prediction. The enclosure also lengthens the decay, so the character of the sound at the receptor is more continuous than the source suggests.

Handle it in one of three ways, and say which you used.

1. A three dimensional acoustic model of the courtyard, with surface absorption coefficients stated.
2. A calculation including reflection terms for each enclosing surface, with the assumptions set out.
3. A measurement of a comparable installation in a comparable enclosure, with the differences explained.

What is not acceptable is a hemispherical calculation with a sentence noting that reflections may increase levels. And be explicit about the courtyard geometry: plan dimensions, wall heights, surface finishes, whether the yard is open to the sky, and the position of the receptor windows relative to the plant.

Where the plant is proposed at roof level instead, the propagation case changes entirely and often improves, so test that option and report the comparison even where the client has already decided.

Rating level and character corrections

Build the rating level transparently, in a table a reviewer can check line by line.

Every correction needs a reason. Fan and compressor noise frequently carries a distinguishable tone, and a report that applies a zero tonality correction to a condenser without explaining why will be challenged. Cycling plant attracts an intermittency correction. Applying the standard's ranges honestly is what makes the conclusion defensible.

Then interpret the excess in context rather than mechanically. The standard treats a larger excess as indicating a greater likelihood of adverse impact, and it also requires the absolute level, the character of the sound and the sensitivity of the receptor to be taken into account. Say what the context is here: a residential courtyard at night, with windows likely to be open in summer, is a sensitive context and should be described as one.

Attenuation options and their effect

Present the options as a hierarchy with a figure against each, showing the rating level before and after.

• Relocation, to roof level or to a less enclosed elevation.
• Plant selection, choosing a larger slower fan over a smaller faster one.
• Acoustic enclosures and lined plenums around condensers.
• Attenuators or silencers in extract and supply ductwork.
• Acoustic louvres to the courtyard.
• Anti-vibration mounts and flexible duct connections, for structure-borne transmission.
• Operational limits, such as reduced night-time capacity or restricted hours.

Operational limits belong last, because they will become a condition and they constrain the business. As an illustrative example, a scheme relying on refrigeration being switched off between 11pm and 7am is not a scheme, and an officer will say so.

Design in headroom. A proposal that lands exactly on the condition limit will fail a verification test once the plant is dirty, the filters are loaded and the fan is running faster than the design point.

Conditions the council will expect

Three conditions, and it is worth offering wording for all of them.

A numerical limit, expressed as a rating level relative to the background sound level at a defined assessment position, with the method named. A requirement to submit a scheme of attenuation for written approval before installation. And a verification test by a suitably qualified person within a stated period of the plant becoming operational, with the results submitted and any remedial works carried out.

Negotiate the numerical limit before the decision. A condition requiring the rating level to be 10 dB below background at a courtyard facade three metres from the plant may be undeliverable, and discovering that after permission is granted leaves you applying to vary a condition you have already breached.

Keep the acoustic work consistent with the rest of the submission. The extract route in the Ventilation and Extraction Statement has to match the duct run the attenuator sits in, any Odour Assessment has to assume the same discharge point and velocity, and the Planning Statement should summarise the position in a paragraph rather than leaving the officer to read three technical appendices.

And remember that planning permission is not a defence to a statutory nuisance complaint. A condition met on paper and a neighbour kept awake are not the same thing, which is the practical reason to build in margin. The full methodology and reporting expectations sit in the Noise Impact Assessment.

Enter your postcode on PlanScope to see which reports a change of use to a restaurant 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. Councils usually expect a noise assessment to be prepared by a suitably qualified author, and professional review is strongly advised. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.