It’s tough to beat the argument that even the basic green roofs are more pleasing to the eye than black-tar and asphalt roofs. Yet, the recent surge of interest in green roofs is due to environmental; not aesthetic reasons. The tradition of green roofs is strongest in Europe and most documented benefits of green roofs originate from European countries. Only recently, the data coming from the US, Canada, Asia, and Australia suggests that green roofs can be beneficial in other places too, when a carefully considered design is combined with the climatic conditions, professional installation and maintenance. All these can guarantee a long-term life of green roofs.
It is sometimes said that the benefits of green roofs are as many as there are green roofs. Evidently, the benefits are many with countless virtues being impossible to quantify. Being dependent on local circumstances is unwise to generalize those benefits. Some advantages are, however, well-documented and worth considering.
Reduce Energy Costs
One appealing reason for homeowners to install a green roof is that it will reduce energy costs. In certain conditions green roof will act as an effective insulator. In others, thanks to a thermal mass effect it will act to reduce the temperature gradient above and under the roof as the system absorbs and then releases heat. The most significant energy impact of green roofs is the reduction of heat flow into buildings during hot weather, reducing the need for air conditioning and thereby annual energy costs. On older buildings, predominantly those that lose heat through the roof, green roofs will decrease heating costs in winter.
Green vs. white roof
The so called cool roofs, especially white roofs are also associated with reduced energy costs. However, white roofs must be cleaned regularly to stay reflective and deliver the optimum performance. In addition, white roofs do not offer the full range of benefits that properly designed and maintained green roofs do. Reflective roofs that have a single-ply membrane are significantly less enduring than a green roof. Frequent replacements make such roof both more costly and less environmentally sustainable.
Beat urban heat
A huge environmental concerns arise because of vast areas of impervious surfaces. Temperatures in urban and suburban areas are 2-11°F warmer compared to nearby rural areas. This creates the so called “urban heat island effect”, that causes the temperature to reach levels dangerous to health. Green areas help keep urban areas cooler, and green roofs can help in that area. According to measurements, on a hot summer day the temperature on a green roof is much lower than that on an nearby conventional roof.
Increase market value of a building
According to a recent research, green buildings hold a premium position in the marketplace. Buildings certified by the U.S. LEED or the Department of Energy’s Energy Star program obtained higher rents and benefited from higher occupancy than similar buildings with conventional roofs. The certified buildings, especially LEED certified buildings also attracted higher sales prices per square foot. Owners of buildings with green roofs frequently cite the savings on operational costs unrelated to the marketing value.
Reduce storm water runoff
The tendency of turning land into shopping malls with vast areas of impervious surfaces generates an increased storm water runoff. When it rains, water running off conventional roofs picks up and carries deposited pollutants to rivers and other local bodies of water. Contaminants in storm water runoff include fertilizers, pesticides, oil and grease, sediment, salts and acid drainage, pet waste, and malfunctioning septic systems. During hot summer months, stormwater runoff contributes to higher temperatures in rivers and streams, potentially compromising the health of aquatic species with smaller temperature niche.
It is widely documented that that the greatest benefit of green roof is the management of stormwater runoff. Hence, stormwater management has been a leading driver of green roof construction. Green roofs help to minimize runoff from rooftops in all but the worst storms. Even in case of the worst storms, there will almost always be less of the runoff from a green roof than from a conventional roof. Rain runs off a green roof more slowly than off a conventional roof what during storms calms the intense peak flows of runoff. Even the simplest green roofs, with about 4 inches of growing medium, can capture at least 50% of the yearly rainfall and most of the rain that falls in the summer months.
Storm water fees
As the storm water fees become adjusted to reflect the real cost of storm water infrastructure and treatment, offsetting credits for green roofs will help to produce faster return of investment for green roofs.
Increase roof lifespan
Obviously, two most harmful forces for the roof are the UV sun rays which degrade the material’s ability to expand and contract and the daily temperature changes that harm the roof’s flexibility. The plants, growing medium, and other components of the green roof systems moderate the temperature on a green roof by protecting the roof’s waterproofing membrane from the sun’s ultraviolet rays and the harmful effects of temperature fluctuations. Currently about 6 to 9 million tons of discarded roofing materials are added to landfills every year in the US.
Less frequent roof replacement is better for the environment as well as the property owner as they will have primary returns on investment for building a green roof is the resulting longer life of the roofing system. Typical roofing systems have a lifespan of 15 to 20 years when left exposed to the harsh elements. By installing a green roof to protect a roofing system, the lifespan of that system will be extended to 60 years.
Boost appeal for occupants
Some benefits to green roof investment extend beyond pecuniary and environmental enhancements. The intangible benefits are noted in regard to owning, living near, working by, and interacting with green roofs. There’s both documented and anecdotal evidence that people favor to work in green buildings. According to the U.S. General Services Administration, people who worked in green and sustainably designed buildings were 27% more satisfied with their work environment than their counterparts working in a conventional commercial buildings. The greatest occupant satisfaction, with 43% satisfied workers, were identified for buildings certified LEED Gold. Green roofs are also good for medical patients. According to a study completed by Louisiana State University, medical patients recover faster when exposed to views of nature.
Preserve wildlife habitat
Insects and birds are attracted to green roof plants and when properly designed to accommodate birds’ and insects’ need for food and shelter, green roofs can play a vital role in preserving urban biodiversity.
Even simple green roofs will usually provide more visual interest for people living or working in high-rise buildings than conventional roofs, adding soothing color and humane feel to the urban environments.
Beauty aside, the purely utilitarian advantages of green roofs are too many to overlook. Should you decide that the benefits above are appealing enough to you, make sure you arm yourself with literature and non-biased professional advice. Green roofs bring life to the roof, but require commitment on the behalf of their owner, including attention and care.
Learn more about green roofs:
- The Green Roof Manual
- Planting Green Roofs and Living Walls
- Roof Gardens: History, Design, Construction
- Green Roof Construction and Maintenance