Experimental investigation of the sound absorption characteristics of vegetated roofs: Fid-Bau Portal

Experimental investigation of the sound absorption characteristics of vegetated roofs

Connelly, M. / Hodgson, M.

Abstract An experimental investigation of the sound absorption characteristics of vegetated roof substrates and plots has been completed. First, an impedance tube was used to measure the normal-incidence absorption coefficients of substrates and their constituents. Substrates provided significant sound absorption, with coefficients varying from 0.03 at 250 Hz to 0.89 at 2000 Hz. Absorption increased with the percentage of organic matter and decreased with moisture content and compaction. A multi-variable regression model was developed for predicting the absorption of substrates. Secondly, the sound absorption of vegetated roof plots was investigated using the spherical-decoupling method. An optimal method, validated in an anechoic chamber, was used to determine the diffuse-field absorption coefficients of unplanted and planted rooftop test plots. Sound absorption increased with increased substrate depth (without vegetation) and decreased with the addition of vegetation and plant establishment. The mean noise reduction coefficient of established vegetated roof plots, with distinctly different plant communities in substrate depths of 50–200 mm, ranged from 0.20 to 0.63 when evaluated over a two-year period. The results confirm that the sound absorption of vegetated roofs is a function of substrate depth, plant community establishment, and moisture content in the plants and substrate.

Highlights • The absorption of roof substrates and their primary constituents were measured in lab. • 25 vegetated rooftop plots, 25 mm incremental substrate depth, were measured in-situ. • Model inputs - organics, moisture and compaction - predicts the absorption of substrates. • The absorption coefficient of vegetated roofs is not dependent on the gradient of depth. • Plant communities' characteristics affect the level of sound absorption of vegetated roofs.