Green roofs offer many public, private, and design-based benefits.
Mitigate Heat Island Effect
The natural plantings and soils in green roofs mitigate the heat island effect by better modulating temperature fluctuations caused by radiant heating during the day. This leads to lower ambient temperatures in the microclimate surrounding buildings.
Energy Efficiency
Green roofs can help reduce energy costs for a building by acting as another layer of insulation between the inside and outside of the roof. This is most noticeable in intensive green roofs since there is a thicker and more consistent layer of soil, which provides a higher insulating value. The insulating properties of the soil can also help reduce sound transmission through the roof from outside the building.
Stormwater Management & Flood Control
Perhaps the most important benefit of green roofs is that they can reduce the amount of and improve the quality of stormwater runoff from a building site. The soils of a green roof will capture a significant amount of stormwater, which is absorbed and used by the planted material. Any water that is released is done so at a slower and more consistent rate, which helps prevent flooding and runoff that can be destructive to the surrounding environment. The plants and soils also filter the stormwater, which helps clean it of pollutants that can negatively affect the natural surroundings. Many jurisdictions now require building owners to collect stormwater in infiltration basins that clean and slowly release the water back into the ground to help reduce the burden on the sewer systems – green roofs help do this naturally without the need for special infiltration basins or equipment.
Improve Air Quality
The plants on green roofs can capture airborne pollutants, atmospheric deposition, and also filter noxious gases.
Increase Biodiversity
Green roofs can sustain a variety of plants and invertebrates, and provide habitat for various bird species. By acting as a steppingstone habitat for migrating birds they can link species together that would otherwise be fragmented.
- Increasing biodiversity can positively affect three realms:
- Ecosystem
- Diverse ecosystems are better able to maintain high levels of productivity during periods of environmental variation than those with fewer species.
- Economic
- Stabilized ecosystems ensure the delivery of ecological goods (e.g. food, construction materials, medicinal plants) and services (e.g. maintain hydrological cycles, cleanse water and air, store and cycle nutrients)
- Social
- Visual and environmental diversity can have positive impacts on community and psychological well-being
- Ecosystem
Urban Agriculture
- Using green roofs as the site for an urban agriculture project can reduce a community’s footprint through the creation of a local food system.
- These projects can serve as a source of community empowerment, give increased feelings of self-reliance, and improve levels of nutrition.
Reduction of Electromagnetic Radiation
Green roofs are capable of reducing electromagnetic radiation penetration by 99.4%.
Green Roof Considerations
There are a number of things to consider when designing for a green roof. One important item to design for is an increased structural load. This is especially true of intensive green roofs, which can have soil that is two feet deep or more. The structural engineer must factor in the weight of completely saturated soil since the plantings and the soil will hold a significant amount of water.
It is also important to factor in the type and lifetime of the roof membrane that will be used. Green roofs tend to improve the life of the roof membrane because it is completely covered by plantings and isn’t exposed to the sun’s harsh UV rays. However, the membrane may be exposed to plant roots, animals and insects, and fertilizer chemicals. It is important that a protective barrier be used over the waterproofing membrane.
Maintenance is also important to consider when designing a green roof. The owner should understand that a green roof requires routine landscape maintenance, which can vary from occasional to regular and can add a significant ongoing cost. In addition, space should be allocated for storage of maintenance materials. For instance, it may be inconvenient to take a lawnmower to the roof on a weekly basis if there is an area of grass that requires regular trimming.
Extensive Green Roof
Green Roof System Comparison
| EXTENSIVE | SEMI-INTENSIVE | INTENSIVE | |
| Plant Options | sedum, moss, grass | sedum, moss, grass, herbs, flowers, shrubs | sedum, moss, grass, large shrubs, trees |
| Soil Depth | 2″ to 5″ Deep | 5″ to 8″ Deep | 8″ to 30″+ Deep |
| Dry Weight | 4 to 12 kg dry weight | 12 to 18 kg dry weight | 18 to 45+ kg dry weight |
| System Types | Tray, Built-Up | Tray, Built-Up | Built-up |
| Maintenance | Minimal | Occasional / Routine | Routine |
| First Cost | Low | Medium | High |
Technical Details: Green Roofs | Sika Thailand