Our rainwater calculations are right on the cusp of reaching the 90th percentile and earning the full three points (+ regional priority point) for this credit. In fact, our calculations met the 90th percentile until we read the v4.1 Reference Guide and realized that rainfall events equal to or less than 0.1" should be omitted. Due to this change, our civil engineer is double checking all calculations.

Typically our civil engineers follow DOEE as a firm standard when filling out the LEED forms and determining retention requirements. The DOEE regulations are more conservative for calculating on-site retention. This is typically not an issue, but with the rainfall events correction, LEED requirements have pushed past the DOEE requirements.

Does anyone know how USGBC interprets retention in bioretention and porous pavement? For example, DOEE only allows you to count 60% of water captured in bioretentions and a small fraction of the volume of water captured for porous pavement. Is our project team able to use the full stormwater volume captured in porous pavement as part of our rainwater management calculations?