Sound insulation of lightweight extensive green roofs

This paper examines factors affecting the sound insulation of lightweight extensive green roofs. The research had three objectives: (1) To examine the extent to which the sound insulation of lightweight extensive green roofs is affected by the variable conditions of their substrate and vegetation layer (soil's distribution, water content and compaction level); (2) To quantify how sound insulation is affected by the main elements making up the roof (substrate and vegetation layer, drainage layer and added cavity); (3) To identify applications for such roofs in relation to their sound insulation performance. For objective 1, it was found that the variable conditions of the substrate and vegetation layer do not significantly affect the sound insulation properties of lightweight extensive green roofs (variations in Rw of no more than 1 dB). For objective 2, results indicated that the addition of a cavity represents the most effective solution for improving sound insulation (+13 dB in Rw for a 50 mm deep cavity with mineral wool), whilst increasing the amount of substrate or using heavier drainage layers tend to provide more limited improvements in Rw (+3 dB for 25 mm of substrate and +2 dB for gravel vs. lightweight drainage membrane). Finally, regarding objective 3, the systems tested were found to provide appropriate sound insulation for both commercial and residential types of constructions. All the results were obtained from tests carried out on small 1 m2 samples, so their accuracy and validity will need to be identified through comparisons with large scale tests.