Green Roofs - Living Architecture Monitor - Fall 2008 - (Page 29)

over the frequency range of interest. The substrate and green roof materials of gr2 increased the tl over the low-mid frequency range of 50 Hz to 2000 Hz by 5 dB to 13 dB, and in the higher frequency range by 2 dB to 8 dB. This is a significant decrease in low and mid frequency sound level transmission; recall that a reduction of 6 to 10 dB sounds like “half the volume.” The green roof therefore provides the opportunity to eliminate the need for ceiling installations for the purpose of increasing sound transmission loss. Comparable sound transmission loss through the addition of a ceiling and insulation may not even be attainable at low frequencies. In summary, current construction practices, driven in part by sustainable building rating programs, have led to an increased use of lightweight metal roof assemblies and a decreased use of ceilings. Given that current sound transmission models do not adequately predict sound transmission through light-weight roof systems or green roofs, these research findings provide supporting evidence of the improved sound transmission loss properties of green roofs. Sound energy is dissipated in the substrate, and the substrate provides mass loading and damping to the light-weight roof deck. Green roofs will improve tl throughout the full architectural frequency range, which is specifically desirable in residential and institutional occupancies developed below aircraft flight paths. Decreasing transmission of unwanted sound is one of many acoustical benefits of green roofs. The absorption of sound striking the rooftop may also reduce urban noise build-up, the introduction of plants and habitat supported by the green roof may alter the rooftop soundscape by reducing noise propagation and introducing positive sounds. Stay tuned for further research findings and discussion. Maureen Connelly is Director, Faculty at the Centre for Architectural Ecology, School of Construction and the Environment, British Columbia Institute of Technology in Vancouver, BC, Canada. Murray Hodgson is a Professor of Acoustics at the School of Environmental Health and Department of Mechanical Engineering at the University of British Columbia in Vancouver, BC, Canada. The authors would like to acknowledge the funding support of National Science Engineering Research Council, and the industry partners of the British Columbia Institute of Technology, Centre for Architectural Ecology (formally, the Centre for the Advancement of Green Roof Technology). These findings were published in 2008 Conference Proceedings, Sixth Annual Greening Rooftops for Sustainable Communities available on CD at www.greenroofs.org. REFERENCES 1. Connelly, M & Liu, K 2005, Green Roof Research in British Columbia An Overview. Version of Greening Rooftops for Sustainable Communities, May 5-6, 2005, Washington, D.C. pp. 1-17. 2. Sharp, BH 1973, A Study of Techniques to Increase the Sound Insulation of Building Elements. US Department of Commerce PB 222 829, Washington. 3. Friberg, R 1973, Transmission Loss and Absorption Factors for Corrugated Steel Roofs, Insulated on the Outside, Proceedings of Inter-Noise, Copenhagen, 1973, pp.213-217. 4. Alexander, NJH & O'Connor, DE & Orlowski, RJ 1980, Industrial Claddings: Sound Absorption and Transmission, Department of Applied Acoustics’, University of Salford, Salford. 5. Bradley, JS 1998, Insulating Buildings Against Aircraft Noise: A Review, National Research Council, Ottawa, Internal Report IRC-IR-760. 6. Bradley, JS & Lay, K & Norcross, SG 2002, Measurements of the Sound Insulation of a Wood Frame House Exposed to Aircraft Noise, National Research Council, Ottawa, Internal Report IRC-IR-831 7. Oelze, ML & O'Brien, WD & Darmondy, RG 2002, Measurement of Attenuation and Speed of Sound in Soils, Soil Science Society of America Journal , vol. 66, pp.788-796. D http://www.greenroofs.org http://www.rooflite.us http://www.rooflite.us http://www.rooflite.us

Table of Contents Feed for the Digital Edition of Green Roofs - Living Architecture Monitor - Fall 2008

Green Roofs - Living Architecture Monitor - Fall 2008 Contents From the Founder: A Robust Economy Letters Strata - People, Products & Projects: Austin's Hotspot for Habitat & Baltimore Hilton Goes Green A Green Roof for a County Courthouse Research Grant for Design Tool On the Roof With... A New Vue on Downtown Open Space Sound Transmission Loss of Extensive Green Roofs On Target Optimizing for Sustainability First GRHC Green Roof Symposium in Florida Welcome New Corporate Members Professional Calendar Experts Reflect on the Value of the GRP

Green Roofs - Living Architecture Monitor - Fall 2008

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