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Acoustical characteristics of vegetated roofs - contributions to the ecological performance of buildings and the urban soundscape

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Title: Acoustical characteristics of vegetated roofs - contributions to the ecological performance of buildings and the urban soundscape
Author: Connelly, Maureen Rose
Degree Doctor of Philosophy - PhD
Program Interdisciplinary Studies
Copyright Date: 2011
Publicly Available in cIRcle 2011-10-19
Abstract: The multiple benefits of vegetated roofs have been proven to reduce the adverse effects of urban densification on infrastructure, natural systems and health. However, the lack of consideration of the acoustical characteristics and benefits of vegetated roofs has limited the ability of design professionals to implement vegetated roofs as an acoustical design solution for noise mitigation and soundscape enhancement. This research, the first of its kind, addressed this problem by measuring the sound absorption and transmission characteristics of vegetated roofs, and by a case-study comparative analysis of vegetated and non-vegetated roof-top play areas. A sound absorption evaluation of substrates, using an impedance tube method, determined that substrates absorb significant sound, and that porosity, percentage of organic matter, moisture content and compaction are acoustically relevant. A multi-variable regression model, developed to optimize the specification of substrates for sound absorption, indicated that a 12.5% increase in the percentage of organic matter increased sound absorption by 9%. The spherical decoupling method was applied to measure the noise reduction coefficient (NRC) of 25 in-situ roof level test-plots with three plant communities established in viable substrate depths. The NRC of the test-plots ranged from 0.2 to 0.6. Measurements of transmission loss (TL) from an indoor-to-outdoor sound transmission lab commissioned for this research, and field evaluations of vegetated roofs of varied substrate depth, water content and plant species, confirmed that the TL values of vegetated roofs are greater than those of non-vegetated reference roofs by 10 and 20 dB in the low and mid frequencies ranges, respectively. The case-study ambient soundscape analysis of vegetated and non-vegetated rooftop play areas demonstrated that vegetated roofs alter the roof level soundscape by the effect of their sound-absorptive characteristics. Most pronounced was the introduction of sounds of birds supported by the vegetated roof habitats and the sounds generated by people interacting with vegetation on the rooftop. The findings are summarized in design guidelines and application notes for synthesis into the landscape/architectural design process.
URI: http://hdl.handle.net/2429/38090
Scholarly Level: Graduate

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