ABSTRACT
The green roof and green wall systems investigated include the Zinco green roof and the Canevaor green wall substrates, both 20 cm in depth, whose sound absorption properties have been studied in laboratories of the University of Bradford (West Yorkshire, U.K.) and University of Shefeld (Shefeld, U.K.), respectively, in accordance to ISO 10534-29 and ISO 354:200310 (cf. Van Renterghem et al.,11 and in Chapter 4 of this volume). The absorption coefcient of green roof substrate is small, between 0.08-0.2, in the low frequency range (i.e., below 125 Hz). Thereafter, it gradually increases with frequency and is about 0.6-0.7 at frequencies above 200 Hz. In the case of green wall substrate, the absorption coef-cient increases from 0.1 to 0.8 in the frequency range of 50-100 Hz, it then drops to 0.6 at 200 Hz, and reaches a stable value of about 0.7 at frequencies above 200 Hz. All data described above are representative for substrates that are dry. Adding moisture to them had a small effect on the absorption coefcient, which is true for the Canevaor green wall substrate, but not true for green roofs, although other types of substrate may exhibit higher dependence on the water content. This characteristic should be considered when selecting substrate partly as a noise abatement measure in an urban environment. Also, the coverage of substrates by vegetation brings a slight reduction in absorption coefcient at higher frequencies, but some improvements at lower frequencies.12
