Background
Anderson Acoustics was appointed by Kench Consultants to support a planning application for the relocation and replacement of an existing rooftop chiller at Thomas Tallis School in the Royal Borough of Greenwich. The proposed new plant location was within the school grounds but in close proximity to existing residential properties.
The scope of works formed part of a planning‑led programme of baseline noise monitoring, BS 4142 assessment, mitigation design and post‑installation acoustic commissioning. The commissioning assessment was required to discharge a planning condition associated with the installation of fixed building services plant within an operational education environment.
Challenge
The chiller is located within a residential context, with noise‑sensitive dwellings to the north, east and south of the site. The Royal Borough of Greenwich required plant noise emissions to achieve a minimum 10 dB margin below representative background sound levels at the nearest residential receptors, in accordance with local policy and BS 4142:2014+A1:2019.
In addition, planning consent required post‑installation testing to demonstrate compliance under operational conditions, using a methodology suitable for a constrained urban site and avoiding intrusive measurements at private properties.
What We Did
Baseline Noise Survey
We undertook a four‑day unattended background noise survey at representative locations around the school boundary to establish robust baseline sound levels, with particular focus on the lowest (night‑time) background conditions.
Plant Noise Assessment and Modelling
Noise emission limits were set based on the most stringent background levels. A detailed 3D environmental noise model was developed using CadnaA, incorporating site geometry, building screening, façade reflections and conservative acoustic assumptions. This enabled prediction of plant noise levels at all nearby residential receptors.
Mitigation Design
To control noise breakout, we specified 3‑metre‑high acoustic louvres enclosing the chiller on all four vertical sides and open at the top to maintain airflow. The design provided significant attenuation while reducing direct line of sight to neighbouring dwellings.
Post‑Installation Acoustic Commissioning
Following installation, a commissioning methodology was agreed in advance with the Local Planning Authority. The assessment combined:
- On‑site verification of installed mitigation and soundproofing measures;
- Attended sound measurements close to the plant to isolate its specific noise contribution, with corrections applied for residual rooftop noise;
- Unattended monitoring at a representative residential receptor
Noise impact was evaluated against night‑time background sound levels with the chiller operating at peak typical duty, supported by observations to identify any tonal, impulsive or intermittent characteristics.
Outcome
The commissioning assessment confirmed that the installed plant fully complies with the planning condition at all assessed receptors. Results demonstrated that operational noise levels were:
- Up to 5 dB below the planning limit at residential properties to the east
- At least 10 dB below the limit at the nearest receptor to the north
- At the permitted limit at the apartment building to the south
No tonal, intermittent or impulsive characteristics were identified, and unattended monitoring showed no discernible increase in ambient noise levels during plant operation. No additional mitigation was required.
Conclusion
This project demonstrates our ability to deliver planning‑led environmental and building acoustics support, from baseline assessment and mitigation design through to post‑installation verification. The commissioning approach combined proportionate on‑site measurement with detailed modelling to demonstrate compliance under conservative assumptions.
The completed assessment provided clear, auditable evidence to support discharge of the planning condition, confirming that the installed plant operates within agreed acoustic limits while safeguarding residential amenity.
Project Progress
Planning permission was granted by the Royal Borough of Greenwich on 3 September 2025, with post‑installation commissioning testing undertaken during the February 2026 half term to minimise disruption to the operational school.
