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.”
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 (firstname.lastname@example.org) is associate editor of BUILDINGS.