Green Roof Technology

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16/2/2012 UC SUMMER SUSTAINABILITY RESEARCH SCHOLARSHIP GREEN ROOF TECHNOLOGY – RESEARCH, DESIGN AND IMPLEMENTATION OF A GREEN ROOF AT THE UNIVERSITY OF CANTERBURY (EcoFriendly, 2008) Nathaniel Claridge | Luke Edwards i EXECUTIVE SUMMARY In cooperation with the University of Canterbury Sustainability Office and the Department of Civil and Natural Resources Engineering, this study aimed to identify and investigate the benefits of green roof systems and how they could be implemented in Chris
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  i   16/2/2012 (EcoFriendly, 2008) Nathaniel Claridge | Luke Edwards   UC   S UMMER S USTAINABILITY R ESEARCH S CHOLARSHIP G REEN R OOF T ECHNOLOGY  –   R ESEARCH ,   D ESIGN AND I MPLEMENTATION OF A G REEN R OOF AT THE U NIVERSITY OF C ANTERBURY    1 EXECUTIVE SUMMARY In cooperation with the University of Canterbury Sustainability Office and the Department of Civil and Natural Resources Engineering, this study aimed to identify and investigate the benefits of green roof systems and how they could be implemented in Christchurch conditions. Green roofs have successfully been installed throughout Europe and North America with proven success and are becoming a popular option for stormwater reduction, urban heat island effect mitigation and insulation. In a New Zealand context the Auckland Regional Council has published ‘Extensive Green (Living) Roofs for Stormwater Mitigation’ which was compiled by Elizabeth Fassman, Robin Simcock and Emily Voyde. This technical report publishes work and findings from green roof projects that were completed in Auckland; namely the University of Auckland Green Roof and the Tamaki Mini Roofs. ‘Extensive Green (Living) Roofs for Stormwater Mitigation’ is the only official New Zealand set of guidelines and covers comparison to overseas standards, substrate development, site construction, plant criteria and selection, structural analysis and codes and technical implementation. The document goes into extensive detail regarding substrate testing, development and properties which this report does not cover. The Auckland Regional Council document has been used as a guide to green roofs for our study and along with a detailed literature review has allowed a knowledge base to be gained. Unlike Auckland scenarios, which took a development approach, our goal is to establish a green roof in Christchurch from proven materials, with the intent to monitor the system and provide data to emphasize the effectiveness of green roofs in local conditions. The system consists of vegetation grown in a predominantly mineral substrate of varying depths, atop drainage and protective layers. The substrate material is engineered to be lightweight yet with a high water holding capacity – characteristics which are often at odds to each other. Much research has been completed into the ideal make up of a green roof and the results are varied. However the prevailing conclusion is that a green roof system should be designed to optimize the intended purpose and to suit the local conditions. The structural capacity of a building, particularly for a retrofit application is often the limiting factor for design specifications and it is necessary to account for the complete saturated system weight in calculations. In such a case the substrate depth and the vegetation have to be chosen to meet these criteria. However research has shown that even thin substrate layers can still provide positive stormwater retention along with other benefits. Where weight is not an issue deeper ‘intensive’ systems can be installed which allow for a diverse plant pallet that may require maintenance. Shallower ‘extensive’ systems are common options where maintenance is intended to be minimised. Plant growth is dictated by the substrate depth along with climatic conditions and it is necessary to choose plants that are hardy and/or suited to local conditions for green roofs. The vegetation holds the substrate together along with playing the vital role of evapotranspiration, transpiring water from the system back into the atmosphere along with direct evaporation.  2 As a result of a number of large earthquakes Christchurch faces a large rebuild which encompasses much of the central city. A clear desire from the public was to have a greener city and green roofs stand as an appealing option if such a path is taken. Green roofs will provide habitat establishment and ecological corridors for wildlife along with enhancing the visual appeal of the city. Due to urbanization cities face a growing problem with the pollution of stormwater and the ability of green roofs to decrease runoff volumes from roof tops may provide one of the largest benefits to Christchurch. This report elaborates on the benefits of green roof systems, explores the characteristics associated with material and vegetation selection and outlines the necessary structural considerations; culminating with the design schematic for implementation of a green roof at the University of Canterbury.  3 CONTENTS Executive Summary ....................................................................................................................................................... 1   List of Equations ........................................................................................................................................................ 5   List of Tables .............................................................................................................................................................. 5   List of Figures ............................................................................................................................................................. 5   List of Appendices ...................................................................................................................................................... 6   1.0 Research Objectives ................................................................................................................................................. 7   2.0 Introduction ............................................................................................................................................................. 7   2.1 Benefits ................................................................................................................................................................ 8   2.2 Prominent Green Roof Examples in New Zealand: Retrofit and New Build ........................................................ 9   2.3 Climatic Conditions of Christchurch................................................................................................................... 10   3.0 Hydrological Considerations .................................................................................................................................. 11   3.1 Hydrological Balance ......................................................................................................................................... 11   3.1 Evapotranspiration ............................................................................................................................................ 13   3.2 Substrate Permeability ...................................................................................................................................... 14   4.0 Substrate and Vegetation considerations ............................................................................................................. 15   4.1 Substrate Composition ...................................................................................................................................... 15   4.2 Vegetation ......................................................................................................................................................... 17   5. Structural Considerations ........................................................................................................................................ 20   5.1 The Importance of Limiting the Structural Load ................................................................................................ 20   5.2 Determination of the Additional Permanent Load, G ........................................................................................ 21   5.3 Worst Case Loading – Saturated Drainage Layer, S u  .......................................................................................... 21   5.4 Contribution to Seismic Loading of the Structure ............................................................................................. 21   5.5 Wind Loading Considerations ............................................................................................................................ 22   6.0 Case Study – Experimental Green Roof at the University of Canterbury .............................................................. 22   6.1 Site Selection ..................................................................................................................................................... 22   6.2 Hydrological Calculations ................................................................................................................................... 24  
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