Water quality and lifecycle assessment of green roof systems in semi-arid climate

Non-point source pollution contributes significantly to stormwater contamination in urban areas. Low impact development (LID) techniques and technologies are developed as a response to these challenges. Green buildings incorporate environmentally responsible and resource-efficient technologies to reduce environmental impacts over their life cycle. Green roof systems are broadly recognized as LID practices that may improve urban environmental quality by reducing stormwater runoffs. Potential impact of green roofs on the quality of runoff may be a deterrent to wider application of green roof systems. Organic and inorganic fertilizers in growing media, for example, may contaminate runoff and generate non-point source pollution. Recently, various environmental assessment methods have been developed to assess the environmental performance of green building technologies. Methods developed to date, however, are insufficient for accurate quantitative estimation and evaluation of triple-bottom-line (TBL) sustainability performance objectives (i.e. economic, environmental, and social) in the context of green building technologies. This study has two main objectives. First, it aims to investigate the performance of green roofs in the context of runoff water quality in the semi-arid environment of Kelowna, British Columbia, Canada. An experimental investigation has been conducted to enhance green roof performance by addition of a supplemental filtration layer. Runoff and precipitation samples were analyzed for water quality parameters including pH, nitrate and ammonia. In the next step, a quantitative sustainability evaluation framework for green building technologies was developed. The proposed framework integrates fuzzy-analytical hierarchy process (FAHP) integrated with a ‘cradle-to-grave’ life cycle assessment to address interactions and influence of various TBL criteria. The experiment results showed that the generic green roofs runoff is acceptable for domestic reclaimed water used under Cnadaian guidelines for domestic reclaimed water. The analysis shows that green roofs are able to reduce non-point source nitrate and ammonia concentrations. The installation of extensive green roofs could decrease a large amount of non-point source nitrate and ammonia emissions in an urban area during their lifespan. The utility of the FAHP approach is demonstrated by comparing sustainability performance of two generic green roof systems with a conventional roof. The results show that an ‘extensive’ green roof system is a more desirable option in terms of long-term sustainability performance criteria.Applied Science, Faculty ofEngineering, School of (Okanagan)Graduat