Life cycle assessment (LCA) is used to evaluate the benefits, primarily from reduced energy consumption, resulting from the addition of a green roof to an eight story residential building in Madrid. Building energy use is simulated and a bottom-up LCA is conducted assuming a 50 year building life. The key property of a green roof is its low solar absorptance, which causes lower surface temperature, thereby reducing the heat flux through the roof. Savings in annual energy use are just over 1%, but summer cooling load is reduced by over 6% and reductions in peak hour cooling load in the upper floors reach 25%. By replacing the common flat roof with a green roof, environmental impacts are reduced by between 1.0 and 5.3%. Similar reductions might be achieved by using a white roof with additional insulation for winter, but more substantial reductions are achieved if common use of green roofs leads to reductions in the urban heat island.
This paper details the role of infrastructure in promoting sustainability at the neighbourhood scale. A sustainable neighbourhood design process is outlined and the importance of adopting a systems perspective and considering infrastructure interconnections is emphasized. The performance of local infrastructure systems (e.g., buildings and local transportation network) is influenced by interactions with the greater urban region and with other local infrastructure. Through a broad review of the literature on transportation, water, building, and urban forestry systems, this paper identifies many of these extra- and inter-neighbourhood interactions. The paper concludes that it is difficult to achieve neighbourhood sustainability objectives without infrastructure systems at the urban scale that support these micro-scale goals. Furthermore, interactions between local infrastructure systems can have a positive or negative impact on infrastructure performance and environmental impacts. Careful consideration of these relationships during neighbourhood design could yield significant improvements in infrastructure resource efficiency as well as reductions in pollutant emissions and overall costs.Key words: sustainable neighbourhood design, infrastructure systems, transportation, water, buildings, urban forestry.
When is it better to retrofit a building as opposed to demolishing and rebuilding it? Life cycle environmental and economic analyses are used to address this question through the study of a typical four bedroom detached house in Toronto. Three vintages of the reference house are used: 1930s solid masonry; 1960s wood frame; and post oil crisis, 1980s wood frame. Retrofit studies considered include insulating the attic and basement walls and air leakage sealing. Over a 40-year life cycle, the rebuild option has lower life cycle energy, global warming potential, and air pollution, which are predominantly associated with building operation. But the retrofit options have lower water pollution, solid waste generation, and weighted resource use, associated with material flows. The retrofit options also have lower life cycle economic costs than rebuilding. In this respect, the preferred options are basement plus air leakage sealing retrofit for the 1930s house, basement retrofit for the 1960s house, and no change for 1980s house. There are ways to overcome the trade-off in negative environmental impacts between retrofitting and rebuilding, such as use of renewable energy sources or re-use and recycling of deconstruction and demolition materials in new construction.Key words: life cycle assessment, life cycle costing, building retrofits, sustainable development.
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