Green Roof Benefits

Green Roof Benefits

Let us first try to understand what exactly is a green roof. It is a roof of a building that is covered with vegetation, either partially or completely, over a water proofing membrane. It is a proper method of growing plants on the roof top and does not refer to green colored roof tiles. Green roofs are also known as "eco-roofs" and are divided into two main types, namely, intensive and extensive. There is semi-intensive roofing as well which requires less deep soil than intensive roofing. Along with the depth of soil, intensive roofing, often referred to as traditional roof gardens, require feeding, irrigation, more labor and overall maintenance. Extensive roofing, on the other hand, is self-sustaining, grown on a very thin layer of soil and requires less maintenance, probably just a yearly weeding or so.

Benefits of Green Roof

Through these green roofing systems, both humans and the environment benefit equally and so these green roofs are gaining popularity day by day.

Natural Habitat for Birds and Insects

Man has captured major areas of land and transformed them into huge buildings which has severely affected the environment and the natural habitat of birds and insects. This applies especially to urban areas where the landscape is sealed by human building activities. But green roofing compensates for that. It creates a natural habitat for creatures like bees, grasshoppers and other insects, who find their food on these roofs and feel closer to their natural habitat.

Energy Efficient

Modern roofs need a lot of energy to moderate the temperatures in winter and summer. Whereas green roofs offer greater insulation and reduce the amount of energy required for moderating temperatures, thus making them energy-efficient.

Maintains Fresh Air

We all know that plants absorb carbon dioxide and release oxygen. The grass or the plants on the green roof not only absorb a huge amount of carbon dioxide but also absorb a number of pollutants present in the air. This green vegetation becomes a kind of natural air conditioner preventing air pollution.

Retains Storm Water

As vegetation requires a water supply, there is an inbuilt water retention layer in the green roof system. This layer is beneficial to retain otherwise wasted storm water. When it rains, because of this water retention capacity, you don’t have to water the green roof vegetation. It uses the rainwater and prevents wastage. During heavy rains, rainwater runs off the flat or slanting roof and causes tremendous overflow in the sewage. A green roof prevents this overflow by slowing down the velocity and volume of running water. Researchers have also found that the nitrogen and phosphorous in rainwater is reduced by a green roof system.

Protects the Roof

During the construction of the structure/house, every builder installs a water proofing membrane to protect the structure/house from difficult weather conditions. Many people think that green roofing might adversely affect the water proofing membrane of the roof. But rather, it protects the membrane from ultraviolet radiation and micro-tearing caused by the constant exposure to weather fluctuations.

Increases Aesthetic Value

Green roofs can compensate for the lost greenery in urban areas and increase the aesthetic value of an area. Your building will look beautiful, coated with green vegetation. These roofing systems can serve as local community gardens. In addition to the attractive look, it will also create a natural atmosphere around you, causing physical and psychological benefits like reducing stress levels in people and keeping them physically fit.

Offers Recreational Space

Nowadays, there is no space left for recreational activities like social gatherings, kids’ activities and other community functions. Green roof systems are capable of offering space for all these activities. People can start their own small-scale cultivation and experience the pleasure of gardening.

Increases Property Value

As green roofing is highly energy-efficient, it can act as an incentive for people who are interested in green roofing systems and their benefits. It will increase the market value of the building and fetch the owner, a great share of profit. It becomes an important asset to the property for which consumers are ready to spend hundreds of dollars. According to studies carried out in the U.S. a green roofing system can add almost 15% to the property value.

Every useful thing has some negatives or drawbacks. Green roofing too, has a few disadvantages. I just want to make you aware of some difficulties associated with such a roofing system. Firstly, it weighs a lot and old buildings might not be able to bear it. So be careful before you install it on a very old building. Secondly, the method of building a green roof system is a little difficult, and if you make even a small mistake, everything might just go down the drain. Lastly, the initial cost of green roofing is considerably high. Hence, if you have proper way out for the above difficulties, go ahead and install a green roof system.

Green on the Go

ESRI’s green roof provides many benefits, including adding 700 square feet of usable space without increasing the rent. The company makes this space available to employees and has even used it for customer receptions and employee gatherings.

Green on the Go

The green roof at ESRI Canada reinforces the company’s brand as an environmental leader. The project includes a space for outdoor meetings, gravel walkways, and plantings that incorporate sedums, herbs, and scented plants to create an interesting texture.

Green on the Go

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Photos courtesy of Scott Torrance Landscape Architect Inc.

Green on the Go

ESRI installed pre-planted trays and gravel trays on top of the building’s existing 2-foot by 2-foot pavers that act as ballasts, allowing the roof to be returned to its original state if ESRI relocates.

Green on the Go

Unlike traditional built in place systems with individual layers of components, modular roofing systems consist of pre-planted trays that include all components. These trays are delivered to the roof and then installed.

Green on the Go

As building owners and cities realize the positive impacts and potential benefits of vegetated roofs – both on individual buildings and areas as a whole – the number of green roofing projects is growing.

From Chicago’s well-known Millennium Park, a 24.5-acre intensive green roof that was completed in 2004 and designed to conceal a parking structure and transportation infrastructure while providing public green space – including an outdoor music facility and a free culture venue – to more recent and much smaller (less than 200 square feet), extensive green roofing projects on individual university buildings – including examples at Kansas State University, Iowa State University, and Cornell University – green roofs are sprouting up everywhere.

As the projects become more popular and widespread, the methods used to create them become more varied. Traditionally, all components of a green roofing system were individually transported to the rooftop where the system was built in place, which is a time-consuming and labor-intensive process. Now there are two main options – traditional built in place systems and modular systems.

With modular systems, all key components of the green roofing system are integrated into relatively easily moved and installed trays. They include many of the same benefits as traditional vegetated roofing systems, along with a few additional benefits not provided by these built in place systems.

GIS Giant Goes Green

ESRI Canada, the Canadian component of ESRI, a company focused on geographic information system (GIS) solutions, recently installed a vegetated roof at its headquarters building in Toronto. "We’re an environmental company," explains Alex Miller, president and founder of ESRI Canada. "The GIS solutions we provide are used in government, business, and education to manage our world sustainability. We wanted to set an example of what a company could do to improve our environment."

The company opted to install a modular system, rather than a traditional system, on the paved terrace adjacent to its 9th floor offices, providing an additional 700 square feet of usable space without increasing the rent. "The modular design allowed us to have a green roof that was fully grown upon being installed, instead of requiring another few years of growth," he says. "It also allowed for easy installation and removal without doing any damage to the building’s roof structure." One reason for this concern, and consideration, is that ESRI leases its office space – the company does not own the property.

The building already had the additional structural loading capacity needed for a vegetated roofing system. "The structural loading capacity was built in, so even with the snow load we were able to get 6 inches of growing medium in certain areas," says Scott Torrance, Scott Torrance Landscape Architect Inc. the company behind ESRI Canada’s green roof. "Then in other areas, along the beams, we were actually able to get 2 feet of depth of soil, and right on top of the columns we were able to point-load trees."

The plants ensure year-round interest, as a variety of plant species including sedums, grasses, evergreens, and flowering plants were chosen. Staff members also wanted trees, which aren’t an easy feat to include in extensive green roofing projects, as they are heavy and require a relatively great depth of growing medium. Torrance opted for Hindu Pan pruned Scotch pines, as Scotch pines are very drought tolerant and the Japanese pruning technique keeps the tree in scale with the size of the planter.

More than 40 different species of plants were used, along with 4-inch- and 6-inch-high modules. Shrubs were planted in 2-foot high planters, while the trees were planted in 4-foot-high planters.

Raise the Roof

With traditional built up vegetated roofing systems, each component of the system is transported to the site and up to the roof. The soil used in the system is often blown up onto the roof. “The ESRI building is a glass building, so blowing soil up nine stories could have been a bit of an issue,” Torrance says. “When it gets that high, the blower tube resonates quite a bit and you don’t want a giant resonating tube right beside an entire glass building. But, a bunch of trays can be brought up to the site.”

Modular systems provide the filtering component, drainage capacity, growing medium, and plants all in one tray, providing for relatively easy and quick installation. “Literally, the ESRI garden was built and finished within a few days,” he says.

One option for modular roofing systems, and an option that ESRI Canada chose to include when designing its roof, is that fully pre-planted trays can be transported to the roof and installed, providing an instant green roof. “Modules can be grown in and hardened off at a nursery off site, well in advance of construction of the actual roof,” explains Linda  Velazquez, ASLA Associate, GRP, LEED AP, and publisher and design consultant of greenroofs.com .

“It’s instant,” says Torrance. “You don’t see a lot of bare earth like you do even in a landscaping project at grade. The whole project comes in as done, it looks completed. That allows a building owner, a tenant, anybody that is building this roof garden, to really present a strong image of success on the opening day. ”

Modular Includes Mobility

Mobility is one advantage of modular green roofing systems – both in terms of installation and repair. “There are multiple benefits associated to modular systems as compared to traditional built in place systems,” Velazquez says. “The obvious one is that they are mobile! Why is that important? What if you were a tenant of a building and not an owner? With a modular system, you could literally pick it up and take it with you when you move.”

While ESRI Canada intends to remain in its current location for a long time, incorporating portability into the design provides flexibility and transferability in case the company does relocate. The modular system also allows the company to easily return the area to its paved, pre-vegetated state if the landlord or future tenant doesn’t want the vegetation.

Ready for Repairs

“Another, perhaps more important, strong reason is a simple one,” Velazquez says. “If you need to repair the roof for whatever reason, all you have to do is pick up the modules from the affected area, fix the problem, and then replace them. No digging up the entire system – drainage, overburden (the growing media/engineered soil), filter fabric, etc. and plants.”

Green Roof Benefits

Modular systems still require soil-to-soil contact between trays. But even with the contact and plant roots crossing from one tray to another, because all components of a modular green roofing system are relatively confined into individual trays, only portions around the area of the roof needing maintenance can be removed. “To pull a tray out, you cut it out like a piece of sod on your lawn,” says Torrance. “You could reach down – you would have some spillover, it’s not like pulling out a tray – but all the growing medium is in one thing so you don’t have to shovel it out. It is a much neater way of doing things, for sure.” After the roof is fixed, the trays can then be replaced and the disturbance to vegetation can go widely undetected.

The vegetated roof system can also be easily repaired in the same way. “Even the trays can be replaced if they weren’t doing well with a particular plant or if there was a plant in one area that someone was very allergic to – you could pull out those five trays and ask the modular supplier to give you five trays of a different plant,” he says.

Is Convenience Worth the Cost?

While modular systems offer the same benefits of traditional systems plus a few more, the ease and extra perks of a modular system come at a price. “They still come in a little more expensive than a built up system, but you have the advantage of instant success, lower maintenance, and some lower maintenance costs,” Torrance states. “Those things should even out a little bit, because weeds aren’t as big of a problem because you don’t have as much bare soil and plants are more established, and they have reduced watering needs.”

Raving About the Roof

ESRI Canada is happy with its choice to install a modular green roofing system. “Our building overlooks a busy highway,” explains Miller. “Now, when you go out to the green roof, you can’t tell that there was a highway below because it filters the noise and air pollution. The great visual is stimulating and improves the office environment. It also delivers savings in heating and cooling costs and provides additional usable space without increasing rent. We’ve made the green roof accessible. We’ve used it for a number of customer receptions and employee gatherings over the year.”

Though the project is just a year old, it has been very well received by office staff and members of the Toronto and green roof communities. “We said that we’d like to set an example to others with the green roof,” Miller says. “I believe that we’ve been fairly successful at that.”

Kylie Wroblaski (kylie.wroblaski@buildings.com ) is associate editor of BUILDINGS.

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 Energys 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 roofs waterproofing membrane from the suns 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.


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