Acoustics case study

Noise Impact Assessment


The North Wales Police proposed the installation of an outdoor air handling unit (AHU) to provide sufficient ventilation to one of their sites in North Wales. SRL provided a noise impact assessment to support the planning application for the proposed AHU, to be submitted to the local council.


The location of the proposed AHU is close to residential housing therefore concerns were raised from the local council regarding the potential noise impact on the neighbouring properties. The planning application was initially refused on the basis that a noise impact assessment was required. SRL were appointed to provide a noise impact assessment to predict the impact of noise from the new AHU on the nearest noise sensitive receptors, and propose any mitigation measures if an adverse impact was likely.


SRL provided a noise impact assessment in line with the British Standard 4142:2014+A1:2019 ‘Methods for rating and assessing industrial and commercial sound’ to submit to the local council in support of the planning application. The assessment consisted of an environmental noise survey of the surrounding area to obtain baseline noise levels representative of the nearest sensitive receptors, which in this case are residential properties. Typical background noise levels were measured during the same time of day and night that the AHU is likely to operate. The measured background noise levels were compared to the predicted noise levels from the AHU at the nearest receptors, which were calculated using 3D noise propagation modelling software. The noise model considered the maximum noise levels likely to be produced, the directivity of the AHU’s exhaust and intake louvres, and local topography. We helped the North Wales Police to determine whether attenuators were required on the AHU and whether any additional noise mitigation measures were necessary to prevent adverse impact on the receptors.