855773644-LEED-v5-BD-C-Reference-Guide-Launch-Edition - Page 133

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Option 2. Natural Land Cover Conditions (3 points)

Calculate the difference between the projected runoff volume under the proposed design conditions and the runoff volume under natural land cover conditions that existed prior to any disturbance. Retain (e.g., infiltrate, evapotranspire, or collect and reuse) on-site the increase in runoff volume using LID and GI practices.

For zero lot line projects only Project teams may combine on-site and off-site strategies to retain runoff from the associated percentile regional or local rainfall event for points, according to Table 1. Engage with local or regional authorities to coordinate off-site rainwater management strategies that meet the credit’s intent, such as participating in community-wide rainwater management programs.

REQUIREMENTS EXPLAINED

This credit rewards projects that manage water runoff from the site, using methods that most closely replicate a natural site hydrology process. The system awards points based on increasing thresholds for the percentage of runoff managed on-site, with additional points given if someone collects and reuses rainwater. Projects may also earn points for retaining any excess runoff anticipated due to the new development conditions.

Option 1. Percentile of Rainfall Events

Data from the percentile rainfall event allows design professionals to study changes in precipitation patterns over time, helping owners and designers understand the impacts of climate change. Using this information, projects can successfully implement strategies to mitigate these impacts.

This option requires that teams gather historical rainfall data for the project area. This data must include the amounts of daily rainfall over a minimum 30-year period. With the data collected, project teams must calculate the rainfall amount (depth) corresponding to the desired percentile of rainfall event and the runoff volume. Using the results of the runoff calculations, the project must implement appropriate stormwater management practices with LID and/or GI measures to maintain the runoff on site.

For projects encompassing larger watershed boundaries, it is crucial to ensure that stormwater management requirements comply with the chosen percentile event across the entire watershed. All development within the boundary must meet the same stormwater performance standards, ensuring consistent and effective management of runoff. This approach extends

U.S. Green Building Council LEED v5 Reference Guide for Building Design and Construction, April 2025 Launch Edition 123