Calculate green roof stormwater retention and detention performance. Determine water holding capacity, runoff reduction, peak flow delay, and structural loads using FLL guidelines and ASCE methodology.
For educational purposes only. Not a substitute for professional engineering judgment.
Green roofs provide stormwater management through retention (storing water in substrate and drainage layers) and detention (delaying runoff). Water is removed through evapotranspiration between storm events.
| Type | Depth (in) | Maintenance | Irrigation |
|---|---|---|---|
| Extensive | 2-6 | Low | Not Required |
| Semi intensive | 6-12 | Medium | Required |
| Intensive | 12-48 | High | Required |
Source: FLL Guidelines (2018), ASTM E2397
| Substrate Type | Min WHC | Typical WHC | Max WHC | Dry Density (pcf) |
|---|---|---|---|---|
| Lightweight mineral aggregate (expanded clay/shale) | 0.25 | 0.35 | 0.45 | 55 |
| Engineered mineral media per FLL specs | 0.3 | 0.4 | 0.5 | 65 |
| Organic-mineral blend (higher WHC, lower density) | 0.4 | 0.5 | 0.6 | 45 |
| Expanded shale/slate aggregate | 0.2 | 0.3 | 0.4 | 50 |
Source: FLL Guidelines (2018), ASTM E2399
| Climate Zone | Min ET (in/yr) | Typical ET (in/yr) | Max ET (in/yr) |
|---|---|---|---|
| Arid | 60 | 72 | 84 |
| Semi Arid | 40 | 50 | 60 |
| Humid Continental | 24 | 32 | 40 |
| Humid Subtropical | 36 | 44 | 52 |
| Marine | 20 | 28 | 36 |
Source: USGS, NOAA Climate Data