For projects that include open space, what is the minimum percentage of rainfall that must be managed?

For projects that include open space, the requirement is to manage at least 95% of rainfall. This standard aligns with the LEED (Leadership in Energy and Environmental Design) guidelines wherein managing rainfall is crucial for reducing runoff, protecting water quality, and promoting the sustainable use of water resources.

Managing such a high percentage of rainfall helps to recharge groundwater and supports the ecological health of the site. It also minimizes potential flooding and associated issues caused by excess runoff. The emphasis on 95% is part of a broader strategy to encourage sustainable stormwater management practices, which include the use of permeable surfaces, rain gardens, green roofs, and other landscape features that enhance water absorption.

The other percentages listed, while they may reflect certain thresholds or variables in specific contexts, do not meet the rigorous standard set forth in current LEED requirements. The higher percentage reflects an increasing recognition of the critical role that stormwater management plays in overall environmental performance within building design and construction.