APEX GREEN ROOFS: Stormwater Retention Study
A Boston Area Green Roof will Retain ~64% of Storm Water
• Statistical Analysis for 10 -years of Local Rainfall Data (Boston area)
• Runoff Volume Coefficient (lower is better for retention on roof)
Avg Annual = 36%
Winter 59%
Spring 27%
Summer 22%
Fall 35%
• This is essential information for the design of rainwater harvesting systems
Green Roofs Reduce Peak Runoff Rate
Data for 1,2,10 yr storms C1 = .37 C2 = .39 C10 = .42
Reference: Open space/park C = .20 City C = .90
• Statistical analysis for 10 -years of local rainfall data (Boston area)
• Rational Coefficient = peak runoff rate/rainfall intensity (Lower is better)
Pennsylvania State Green Roof Research
