Economic Benefits
Publication Information
| Title: | Regent Park Redevelopment Sustainable Community Design |
| Author Surname: | Dillon |
| Author Firstname: | Consulting |
| Journal/Conference/etc.: | Public Report |
| Date of publication: | 02-OCT-2004 |
| On pages/Number of pages: | 90 |
| Publisher: | Toronto Community Housing Corporation |
Abstract
In 2001, the Toronto Community Housing Corporation embarked on a comprehensive redevelopment study for Regent Park in downtown Toronto. A key component of this study was to design a model community driven by sustainability targets and based on an interdisciplinary approach. The Sustainable Community Design Report documents the process used and the recommendations for sustainable design for Regent Park. The recommendations encompass a fully integrated sustainable design that achieves significant targets for environmental protection and enhancement including: 35% reduction in per capita water use; 75% energy use reduction; 80% reduction in green house gas emissions; significant improvements in stormwater runoff retention, quality and quantity; 35-60% solid waste diversion; improved natural environment/landscape; and reduced environmental impacts from building materials, construction and demolition.
The report includes a portion on economic analysis of green roofs in Appendix 9 where the economics of inverted roof, extensive roof and intensive roofs are compared.
Purpose of Research
The objective of the Appendix 9 of the report titled green roof life cycle costing report is to compare and contrast the life cycle costs of two types of green roofs relative to a traditional protected membrane roofing system.
Modelling Conditions
| Type of green roof studied: | Mixed |
| Size or range of sizes of green roofs studied (square feet): | 385 square meters (4,000 square feet) |
| Type of Construction: | New |
| City or cities: | Toronto |
| States or Provinces: | Ontario |
| Country or countries: | Canada |
| Plant Type: | NA |
| Growing medium depth or range of depths (inches): | NA |
| Other conditions of modelling: |
Only those cost savings that can be estimated and recouped by the investor are considered. Benefits with externalities are not considered.
Investment period: 50 years
General inflation: 2.5%
Energy escalation: 5%
NPV in 2004 dollars
Service life of traditional inverted roof: 22 years
Service life of extensive and intensive green roof: 40 years
Energy cost difference between green roof and benchmark roof for heating is $0.27 per square meter and for heating is $0.35 per square meter for cooling.
Method
A traditional life cycle costing method is used. Various input parameters are determined from the configuration of the building. Only costs and savings that can be attributed directly to the investor are considered. Costs and benefits related to externalities are not considered. Analysis is done assuming a low, high and average estimate of the costs.
Bio-Physical Benefits Addressed
The method consisted of identification of benefits, quantification of the impacts, and monetization of the benefits. All these parameters were developed based on review of existing literature and selecting appropriate models to be used for the purpose.
Research Results
The results indicate that the traditional inverted roof has the lowest LCC. That is, the energy saving ascribed to green roofs are
insufficient to warrant their higher initial, maintenance and replacement cost. The extensive roof exhibits a lower LCC than the intensive roof. The sensitivity of the two green roof investments to a change in life span from 25 to 40 years had little impact on
the results of the LCC. This outcome is primarily a function of using the higher, private sector discount rate (17%) where future costs and costs savings are discounted more heavily. These results make it evident that either the initial capital cost of green roofs would have to be considerably less, or that other benefits of green roofs need to be internalised as positive cash flows, before they would compare favourably with a traditional inverted roof investment.
To underscore the significance of capital costs the sensitivity of the green roof designs relative to that of the traditional inverted roof system was investigate. An analysis was done leaving the traditional inverted roof values unchanged (maintained average values) and the extensive and intensive green roof designs at the low values for capital and maintenance costs for the 40 year life span cases. Only at these lower cost and higher expected life span levels did the extensive roof attained a lower LCC than
the traditional inverted roof by $5,500. The Intensive roof was still $20,000 more expensive than the benchmark roof.
Summary Information
| Summary prepared by: | Hitesh Doshi |
| Date: | 19-MAY-2007 |