Green Roof Benefits
Green roofs offer many public, private, and design-based benefits.
Please Note: while there are similarities among green roofs, each installation is unique. Hence, all technical performance details provided will vary by region, climate, building and green roof type and design. These figures are provided as generic examples only and should not be used for designing projects.
GRHC (Green Roofs for Healthy Cities) Corporate Members and Green Roof Professionals are an excellent source of green roof expertise. Resource manuals are available from GRHC’s Green Infrastructure Store. Online training is available through the Living Architecture Academy. For more site-specific benefits calculations, GRHC members can access the GreenSave Calculator, which lets users compare the costs and benefits of different green roof systems.
Public Benefits
Aesthetic Improvement
- Urban greening has long been promoted as an easy and effective strategy for beautifying the built environment and increasing investment opportunity.
Waste Diversion
Green roofs can contribute to landfill diversion by:
- Prolonging the life of waterproofing membranes, reducing associated waste
- The use of recycled materials in the growing medium
- Prolonging the service life of heating, ventilation, and HVAC systems through decreased use
Stormwater Management
- With green roofs, water is stored by the substrate and then taken up by the plants from where it is returned to the atmosphere through transpiration and evaporation.
- In summer, depending on the plants and depth of growing medium, green roofs retain 70-90% of the precipitation that falls on them; in winter they retain between 25-40%. For example, a grass roof with a 4-20 cm (1.6 - 7.9 inches) layer of growing medium can hold 10-15 cm (3.9 - 5.9 inches) of water.
- Green roofs not only retain rainwater, but also moderate the temperature of the water and act as natural filters for any of the water that happens to run off.
- Green roofs reduce the amount of stormwater runoff and also delay the time at which runoff occurs, resulting in decreased stress on sewer systems at peak flow periods.
- More on the stormwater management benefits of green roofs can be found in GRHC’s half-day course:Integrated Water Management for Buildings and Sites.
Moderation of Urban Heat Island Effect
- Through the daily dew and evaporation cycle, plants on vertical and horizontal surfaces are able to cool cities during hot summer months and reduce the Urban Heat Island (UHI) effect. The light absorbed by vegetation would otherwise be converted into heat energy.
- UHI is also mitigated by the covering some of the hottest surfaces in the urban environment – black rooftops.
- Green roofs can also help reduce the distribution of dust and particulate matter throughout the city, as well as the production of smog. This can play a role in reducing greenhouse gas emissions and adapting urban areas to a future climate with warmer summers.
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