Green Infrastructure: Green roofs consist of a series of layers that create an environment suitable for plant growth without damaging the underlying roof system. Green roofs create green space for public benefit, energy efficiency, and stormwater retention/ detention.
Structural load capacity, how much weight the roof can hold, is a major factor in determining roof design and construction. Green roofs are therefore typically defined as being either extensive or intensive.
- Extensive green roof: an extensive green roof has growing medium ( engineered media) that is 6 inches or less deep
- Intensive green roof: an intensive green roof has growing medium that is more than 6 inches deep
Semi-intensive green roofs represent a roof design intermediary between extensive and intensive roof. The following table summarizes characteristics of the different types of green roofs.
General characteristics of extensive and intensive green roofs (adapted from Green Roofs for Healthy Cities and the Cardinal Group, 2006).
Link to this table.
| Characteristic | Extensive | Semi-intensive | Intensive |
|---|---|---|---|
| Growing medium depth | 6 inches or less | Portions of the green roof above and below 6 inches, with a minimum of 25% of green roof area above or below 6 inches | More than 6 inches |
| Accessibility | Often inaccessible | May be partially accessible | Usually accessible |
| Fully saturated weight | Low: 10 to 35 lb/ft2 (48.8 to 170.9 kg/m2) | Varies: 35 to 50 lb/ft2 (170.9 to 244.1 kg/m2) | High: 35 to 300 lb/ft2 (170.9 to 1464.7 kg/m2) |
| Plant diversity | Lower | Greater | Greatest |
| Cost | Low | Varies | High |
| Maintenance | Varies, but generally lower than for intensive green roofs | Varies | Varies, but generally higher than for extensive green roofs |
| Stormwater management | Best cost-benefit balance | More growing medium and more vigorous plant growth provides marginally greater stormwater volume benefits | More growing medium and more vigorous plant growth provides marginally greater stormwater volume benefits |
Related pages
- Green roofs
- Overview for green roofs
- Types of green roofs
- Design criteria for green roofs
- Construction specifications for green roofs
- Assessing the performance of green roofs
- Operation and maintenance of green roofs
- Calculating credits for green roofs
- Cost-benefit considerations for green roofs
- Plant lists for green roofs
- Case studies for green roofs
- Links for green roofs
- References for green roofs
- Supporting material for green roofs
- Green roofs terminology and glossary
- Green roof fact sheet
- Requirements, recommendations and information for using green roofs as a BMP in the MIDS calculator
This page was last edited on 23 November 2022, at 22:44.