Acoustic properties of green walls: Absorption and insulation

In the past few decades, the issue of environmental quality in the urban environment is a recurring theme. Green walls and roofs have demonstrated great efficiency in the attenuation of adverse effects such as heat islands. The thermal characterization of these systems are well studied, however few studies have been carried out on their acoustic potential. The characterization of the acoustic performance of green walls may provide better results for the acoustic simulation of urban environments where such elements are employed. This paper presents experimental results of the sound absorption and insulation tests for a modular system of vegetable panels. Each module was composed of a baseplate made of laminated plywood, equipped with 9 geotextile bags in which was inserted a highly porous substrate, and grown a specie of plant with high leaf density. Absorption tests were conducted in a reverberation room, where sound absorption coefficient over frequency was measured. The sound absorption of the panels were analysed in three different situations, in order to better characterize the contribution of each part of the system: (I) baseplate + geotextile bags, (II) baseplate + geotextile bags + substrate, and (III) plate base + geotextile bags + substrate + vegetation. Façade insulation tests were performed with the same types of sample placed on a concrete block façade of a small building. Results showed a significant increase of sound absorption coefficients at the whole spectrum when substrate and vegetation were inserted on the baseplates in each situation. Both the standardized level difference and the weighted standardized level difference showed a small improvement in the insulation for the sample with vegetation.