St John’s Square – ASHP Acoustic Enclosure

Following an initial report by Sound Solutions that highlighted a number of challenges, Sound Planning recently completed a project at St John’s Square in Clerkenwell, London.

The project focused on an air conditioning unit installation that was subject to an environmental noise impact assessment. The assessment was carried out in accordance with British Standard BS4142:2014 to establish the potential noise impact of the two air conditioning installations on the nearest neighbouring properties. Installations of this nature are governed by the Noise Policy Statement for England (2010), which is a legislation aimed at ensuring noise does not impact adversely on people’s health and quality of life.

The assessment was also required to consider the potential noise impact of a proposed third unit that may be installed in the future. Appropriate noise mitigation measures were then recommended to adhere to the local council’s specified noise criteria. Units were installed externally to provide both cooling and heating to offices on the site. Located 3m from neighbouring first-floor office windows and 8m from the nearest noise-sensitive residential living room window, they were to be restricted to daytime use only – from 7am to 11pm.

The environmental sound survey identified that the units’ rating levels were predicted to be below the measured background sound level, indicating a low impact in accordance with British Standard BS4142:2014. However, the rating levels failed to meet the local authority’s noise criteria of 5dBA below the measured background level. As a result, noise mitigation was required at the site to meet the council’s specifications. The challenges faced by Sound Planning included finding a suitable solution for the confined space available, where adequate airflow was required. A concrete overhang further exacerbated the problem, especially due to the units’ close proximity to noise-sensitive offices.

The air conditioning units had vents to the top and the sides, so any form of noise mitigation had to address the noise output at both points. It was recommended that an enclosure, consisting of acoustically treated louvres, should be constructed around the units in question. An acoustic louvre screen around the exposed perimeter of the plant was recommended, in addition to a solid roof structure, as the site was overlooked by the nearest neighbouring premises. The recommended enclosure was predicted to provide 17dB of attenuation.


The subsequent noise-reduction measures by Sound Planning successfully reduced the existing units’ rating levels, conforming to the local authority’s noise criteria of 5dBA below the measured background level. The assessment also predicted the measures would facilitate the use of a third air conditioning unit, should it be installed at a later date.

The rating level of the two existing units was reduced from +2dB to -10dB as a result of the acoustic solution provided by Sound Planning. The prediction for three air conditioning units saw the rating level fall from +4dB to -8dB, indicating the success of the noise mitigation solutions.

The assessment concluded that the installation of the specified acoustic enclosure and anti-vibration footings would facilitate the use of up to three air conditioning units, ensuring compliance with the local authority’s noise criteria and national planning policy. Noise, therefore, should not be a factor that would prohibit the granting of planning permission.

If you require more information on our bespoke solutions, please don’t hesitate to contact Sound Planning. We can provide reliable acoustic solutions to even the most complex challenges.


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