Green roofs offer tangible benefits for end users, inhabitants, owners and the greater community. They can range from economic and ecological to social and aesthetic reasons.
Depending on the type and regional climate, green roof benefits include cost-savings, energy savings, environmental and wellness impacts. Overall advantages of any individual green roof depend on its design build-up, geographic location, surrounding environment and the building itself.
Improves stormwater management
During heavy rainfall, stormwater runoff from surfaces like pavements and rooftops can cause serious problems such as sewer overflow and water pollution. Green roofs slow down the water flow by retaining up to 75% of the rainwater, thus alleviating pressure on stormwater infrastructure.
| Water retention for traditional roof versus green roof (% of rainfall retained)¹ | ||
|---|---|---|
| Standard roof | Green roof | |
| Average retention | 24% | 80% |
| Retention at peak runoff | 26% | 74% |
The table above shows that a green roof retains much more water than a typical roof, thereby slowing down the movement of water through the roof.
Improves air quality and biodiversity
Green roof plants reduce air pollution by filtering out particulate molecules and converting carbon dioxide into oxygen, reducing greenhouse gas emissions.
Roof gardens also boost biodiversity by creating a natural habitat for birds, bugs and butterflies.
The addition of a vegetated roof to an otherwise unused area on a building is beneficial for the surrounding environment. Initial loss of green space and its inherent natural processes like photosynthesis are restored, now just a few stories higher.
Reduces urban heat island effect
More green roofs and fewer dark-colored roofs equal a cooler city. Dark roofs retain heat while plants naturally cool their surrounding environments through evapotranspiration cycles. Plants absorb about 50% of sunlight.
In urban areas where the ambient temperature can be up to 10 degrees Celcius hotter than the surrounding areas, green roofs can help bring the overall temperature down. They can reduce ambient temperature in a city up to 3°C. ²
Building codes, fire-resistance and sustainable requirements
Green roof systems help to meet international green building standards such as LEED, BREEAM, and more.
It creates a naturally fire-resistant layer thanks to the moisture in plants and soil.
"Green roofs are healthy, sustainable and regenerative roof landscapes that help protect our environment by diminishing developmental impacts on our communities. "
Saves energy costs, reduces energy consumption
Green roofs are great insulators. They can reduce peak energy demand by lowering a building’s cooling costs in summer months and heating costs in winter months. In hot weather, green roofs protect the interior from direct heat gain. In cold weather, green roofs create an insulation layer that keeps warmth inside. This increases the R-value – the measure of the green roof material’s resistance to heat flow. By shading the outer surface of the building with a green roof system, it is shown to be more effective than using insulation on the internal side.
They help to reduce costs of mechanical equipment by improving their efficiency. Plants reflect 30% of sunlight, meaning the air conditioning doesn’t have to work so hard.
Green roofs can also be combined with photovoltaics as a solar roof system for extra energy cost savings.
The University of Michigan did a valuation study to compare a 2,000 square meter conventional roof with a green roof across a full range of benefits. Over an estimated lifespan of 40 years, a green roof would save about USD 200,000, of which nearly two–thirds would come from reduced energy costs.
Extends roof life and increases property value
A green roof protects the roof waterproofing membrane from damaging UV rays, freeze-thaw cycling and repeated foot traffic, extending its lifespan. It may double or even triple the roof life span, thereby saving re-roofing costs. Some green roofs in Europe have lasted more than 40 years without being replaced.
Green roofs can improve marketability and increase property value, which adds value to the building thanks to the other benefits noted.
People’s well-being and aesthetics
Greenery is visually stimulating and improves the well-being of people by offering relaxing views and planted space, pleasant urban environment to look at from neighboring buildings above.
Urban amenities and education
Landscaped roofs can be designed as a roof garden with a fully accessible park-like atmosphere, which is a great area for recreation and pleasure. By choosing a green roof, you make the most of otherwise unused space, which can double as urban rooftop gardens or even food production.
You can post informational signs to educate building occupants or passersby to the many benefits of the green roof system.
Sound insulation
Soil and plants are an effective sound insulator. They act as sound insulation material and reduce the noise transmission between the inside and outside of a building. For example, they help reduce sounds of noisy mechanical equipment on the roof or airplanes flying overhead.
Summary - Pros and Cons
| Pros | Cons |
|---|---|
| Reduce energy costs, increase energy efficiency of the building | Higher upfront costs, more expensive to install |
| Saves roofing costs, extends roof lifespan | Weight load increase |
| Increases property value | Requires extra maintenance and time |
| Improves stormwater management | |
| Improves air quality | |
| Reduces urban heat islands | |
| Naturally fire-resistant | |
| Sound insulation to reduce outside noises | |
| Helps regulate temperature in a building | |
| Creates natural habitat for wildlife | |
| Meets green building standards | |
| Urban agriculture opportunities | |
| Improves people’s well-being | |
| Beautiful and visually appealing |
As you can see, the benefits of green roof systems largely outweigh the potential downsides. Green roofs are a sustainable option which benefits the environment, economic factors and general well-being of the community.
Sika offers a full range of inter-compatible systems for green roof buildups, including waterproofing membranes, thermal insulation, drainage boards, vapor control layers, prefabricated accessories, scuppers and drains. Check out the green roof systems that Sika provides.
"When you specify or choose a Sika green roof, you get more than watertight security - you get peace of mind knowing you made the right choice."
References
¹ "Green Roofs in the New York Metropolitan Region, Research Report," Rosenzweig, et. al.
² Santamouris, M. 2014. “Cooling the cities – A review of reflective and green roof mitigation technologies to fight heat island and improve comfort in urban environments,” Solar Energy 103:682–703.