Types Of Green Roofs Research Articles

Numerical evaluation of sound propagating over green roofs

Sound propagation over intensive and extensive green roofs was numerically studied by using the finite-difference time-domain method. The Zwikker and Kosten model was used to simulate sound propagation in the substrate layer itself. The presence of a green roof is mainly interesting in a street canyon configuration, and fits well in the concept of quiet sides. Positive effects of green roofs, relative to fully rigid roofs, are mainly observed at the octave bands with centre frequencies 500 and 1000 Hz. The source type was shown to be unimportant when considering this particular parameter. There is a linear relationship between the fraction of the roof covered with green and the decrease in sound pressure level at the non-exposed canyon. The slopes increase with octave band centre frequency. The width–height ratio of the street canyon configuration has only a limited effect. For extensive green roofs, a pronounced attenuation peak is found when varying the layer thickness, leading to a maximum reduction of up to 10 dB, relative to an acoustically rigid roof, for the octave band of 1000 Hz. A good overall efficiency is observed near the maximum layer thickness (15–20 cm) for this type of green roof. For an intensive green roof with a substrate layer thickness exceeding 20 cm, which is common, positive effects are not influenced anymore by substrate thickness.

Life-cycle cost–benefit analysis of extensive vegetated roof systems

The built environment has been a significant cause of environmental degradation in the previously undeveloped landscape. As public and private interest in restoring the environmental integrity of urban areas continues to increase, new construction practices are being developed that explicitly value beneficial environmental characteristics. The use of vegetation on a rooftop—commonly called a green roof—as an alternative to traditional roofing materials is an increasingly utilized example of such practices. The vegetation and growing media perform a number of functions that improve environmental performance, including: absorption of rainfall, reduction of roof temperatures, improvement in ambient air quality, and provision of urban habitat. A better accounting of the green roof's total costs and benefits to society and to the private sector will aid in the design of policy instruments and educational materials that affect individual decisions about green roof construction. This study uses data collected from an experimental green roof plot to develop a benefit cost analysis (BCA) for the life cycle of extensive (thin layer) green roof systems in an urban watershed. The results from this analysis are compared with a traditional roofing scenario. The net present value (NPV) of this type of green roof currently ranges from 10% to 14% more expensive than its conventional counterpart. A reduction of 20% in green roof construction cost would make the social NPV of the practice less than traditional roof NPV. Considering the positive social benefits and relatively novel nature of the practice, incentives encouraging the use of this practice in highly urbanized watersheds are strongly recommended.

The Role of Water Balance Modelling in the Transition to Low Impact Development

Abstract Low impact development (LID) is increasingly being viewed by local governments and developers alike as a viable approach to stormwater management that can effectively protect aquatic habitat and water quality. LID relies on distributed runoff management measures that seek to control stormwater volume at the source by reducing imperviousness and retaining, infiltrating and reusing rainwater at the development site. Early conventional stormwater management practices tended to focus on stormwater quantity and controlling a few extreme rainfall events, whereas the more frequent storms, which represent the majority of total runoff volume, carry most of the pollutants, and control the geomorphology of streams, were addressed in stormwater quality design practiced during the last decade. These frequent events are most effectively managed with a volume control approach, often described as stormwater source control or Low impact development (LID). Such an approach is described in this paper, demonstrating how water balance modelling can be an effective tool for evaluating and supporting implementation of LID options such as bioretention, pervious paving, numerous types of infiltration systems, rainwater reuse and green roofs. It also discusses recently developed water balance modelling software, including an Internet-based planning tool and a design optimization tool.