Establishing a heuristic framework for effective attenuation of traffic noise transmission in typical naturally ventilated classrooms in urban schools in Gauteng, South Africa

Abstract

This study aimed to investigate the possible means of mitigating noise disturbance in naturally ventilated classrooms that are exposed to road-traffic noise. Specifically, the efficacy of façade design, building orientation, distance from the road and noise barriers was tested to achieve a suitable ambient sound pressure level (SPL) in classrooms. The outcome is a heuristic framework to assist school infrastructure planners and architects in the early stages of a project to choose suitable acoustic interventions. The context was the urbanised province of Gauteng, South Africa, where many new schools are needed and where urbanisation has enveloped many previously suburban schools in traffic noise. Classrooms are typically naturally ventilated with open windows that allow noise in. This increases the classroom ambient noise level which has potentially negative effects on the occupants’ health, well-being and academic outcomes. A computer model of a typical classroom, based on data collected at four Gauteng schools, was used to experiment with various sound attenuation interventions. The modelled results showed that the façade construction material is acoustically inconsequential due to the compromising effect of large openings. A suitable classroom ambient noise level (40 dBA) was only achieved for a building modelled without a barrier at the maximum distance modelled, which was 136 m from the road, provided that the building was perpendicular to the road. Barriers of varying heights (1.5 m – 7 m) were inserted, either at the school boundary (12 m from the centre of the road) or 3 m from the classroom façade. With a barrier, the closest distance from the road at which the target SPL was achieved was at 42.5 m with a 5.5 m high barrier. As the distance from the road to the building increased, the height of the barrier required decreased. Considering a maximum practical barrier height of 3.5 m, the ideal SPL was only achieved for a classroom at least 51 m from the road. Barriers inserted 3 m from the façade were more effective than barriers at the school boundary. A significant SPL decrease (≥ 6 dB) was, however, achieved in classrooms as close as 17 m from the road with the insertion of a barrier (≥ 2 m high), and a suitable signal-to-noise ratio was achieved for a classroom 17 m from the road with a 2.5 m high barrier. These findings are particularly useful for application in existing schools with limited space. The findings provided a data set that was used to develop a heuristic framework as guidance for planners in the early stages of school infrastructure design.