Overview:

Summary: Green roofs cool the surrounding air and reduce building heat through a layer of vegetation or other plants. Green roofs can also serve as additional green space. There are two main types of green roofs: intensive and extensive.

Implementation: Encourage or require green roofs through multiple mechanisms: changes to zoning or codes to include green roofs or requirement for green roofs for developments over a certain size.

Considerations for Use: Green roofs need sufficient structural support and do not work on steep-sloped roofs. Green roofs require maintenance and upkeep every year. Roofs that are open to the public require safety precautions. Intensive green roofs provide more co-benefits (such as stormwater management) are much heavier than extensive roofs and require more structural support, irrigation, and fertilization as well as additional maintenance. Green roofs are generally more feasible and cost-effective in new construction versus retrofits. Given the costs required to install and maintain green roofs, requirements to install them must be carefully considered.

• Policy Levers:
  
  
  MandateMandates are government regulations that require stakeholders to meet standards through building codes, ordinances, zoning policies, or other regulatory tools.
• Trigger Points:
  
  
  City planning processesIncludes city initiatives such as the development of climate action plan, pathway to zero-energy, master plan, transit plan, energy mapping etc.
  Introducing new or updated zoning/codesIncludes codes, zoning requirements or by-laws pertaining to urban planning and building construction activity.
• Intervention Type:
  Green/natural Infrastructure
• Sectors:
  Buildings

Impact:

• Target Beneficiaries:
  Property owners, Residents
• Phase of Impact:
  Risk reduction and mitigation
• Metrics:
  Decrease in temperature at building, Energy savings, GHG emission decrease, Number of permits and total area of completed and in progress projects, Stormwater runoff reduction

Case Studies:

• Toronto Green Roof (ULI, Pg 54)
• Seattle Green Factor Ordinance (UNEP, Pg 204)

Implementation:

• Intervention Scale:
  Building
• Authority and Governance:
  City government
• Implementation Timeline:
  Medium-term (3-9 Years)
• Implementation Stakeholders:
  City government, Private developers, Property owners and managers
• Funding Sources:
  Grants and philanthropy, private investment, Public investment
• Capacity to Act:
  High, Medium

Benefits:

• Cost-Benefit:
  High
• Public Good:
  Medium
• GHG Reduction:
  Medium
• Co-benefits (Climate/Environmental):
  Improve stormwater management, Preserve biodiversity, Reduce air and water pollution
• Co-benefits (Social):
  Build social cohesion, Improve human health, Increase property values, Save on utilities