Changes

*Do not require ground level space, so particularly well suited where ground space is limited or sites with large flat roofs,*May not require additional sewer connections, *Easy to retrofit if structural support and waterproofing are adequate,*Relatively low cost compared to green roofs (no vegetation requirements),*Potential for evaporative cooling and reduction of urban heat island effect.

*Limited application on sloped roofs or sites with small building footprints,*Do not provide any co-benefits such as habitat creation or air quality improvements associated with vegetated practices,*Mechanical systems and other rooftop architectural features must not be adversely impacted by ponded water.