Effect of water content on noise attenuation over vegetated roofs: Results from two field studies

Urban traffic noise is mitigated when propagating over vegetated roofs. It is known from results of laboratory measurements that the sound absorption performance of vegetated roofs is affected by its substrate water content. In a previous study on one extensive green roof, a significant decrease of noise attenuation was found when the substrate water content increased, specifically in the frequency range between 250 Hz and 1250 Hz. This work presents new results from long-lasting in-situ experiments on two extensive vegetated roofs in Eindhoven (Netherlands), together with two different methods for obtaining the results. One scenario involves traffic noise and an artificial noise source is used in the other scenario. The sound pressure level differences over the vegetated roofs, substrate water content and meteorological conditions are measured and collected. Although a descending tendency of noise attenuation with the increase of the substrate water content as in previous research can be confirmed, the extent and frequency of this effect vary significantly between the two vegetated roofs, specifically between 400 Hz and 2000 Hz on the Cascade roof and between 800 Hz and 1000 Hz on the Strijp-S roof.