The Proof Is on the Roof
- By Sandy McCullough
- August 1st, 2006
For many, a drive on Chicago’s famed Lake Shore Drive is an architectural adventure. One passes some of the grandest and most elegant high-rise apartment buildings in the city. Many of these were built in the early 1920s, and some include apartments with 10, 15 or more rooms.
However, a problem — or shall we say an internal conflict — found in many of these buildings centers around their windows. As the buildings age, their windows need to be replaced. And because this can be a costly project, even if it saves the homeowners money in the long run, it is not uncommon for some owners in these buildings to delay replacement for as long as possible.
When qualified building engineers tell owners the windows must be replaced but the owners resist, there is only one thing we can do, says Sam Ambrose, a building engineer.You have to educate them and reeducate them until they understand the problem and the benefits of installing new windows.
Many schools and universities are in a similar situation when it comes to green roofs. Building construction funds are often tight, and even though adding a green roof to a new or existing campus facility has many supporters, many administrators have difficulties accepting the added costs or recognizing the potential long-term savings. For those who support and know the value of green roofs, their only option is to educate and reeducate facility managers and school administrators as to the benefits and features.
Today, although most school administrators and facility managers know what a green roof is, many still consider it European technology. They believe that green roofs are having little impact on the U.S. building or educational industries except in a few localized markets — and mostly on buildings developed by city and state governments.
Often, they voice concerns about green roofs, such as: Do they leak? What about the added weight load to the structure? Don’t the costs of installing green roofs make them prohibitive? And what are the tangible benefits?
Compounding the problem is the fact that extensive research and studies about green roofs are still in short supply. Although green roofs have been monitored and studied in several North American cities, much of that data is only now coming to light. For instance, the Lady Bird Johnson Wildflower Center in Austin, TX, will soon begin a pilot program to explore the value of green roofs and hopes to raise enough money to perform one of the most comprehensive studies ever conducted.
For these reasons, it’s necessary to address some of the concerns and issues related to green roofs — especially the cost benefits — to help educate building professionals and school administrators.
Return on Investment
Understandably, many colleges and universities are concerned about the costs of any new feature installed onto their buildings. And unfortunately, because so many of the green features incorporated into buildings in the 1970s and 1980s were costly and proved to have little return on investment, discussions of the installation of a green roof are often met with some skepticism.
However, a report issued in October 2003 by the California Sustainable Building Task Force states that adding green elements to facilities today can produce significant benefits. For instance, the task force found that, on average, a two-percent increase in upfront costs to help make a facility green could yield life-cycle savings of 20 percent of the total investment. In other words, an initial upfront investment of up to $100,000 to incorporate green building features into a $5-million project — such as the installation of a green roof — would result in a savings of $1 million in today’s dollars over the life of the building.
The actual costs to install a green roof can vary significantly and depend on a variety of factors. These factors include the following.
Size and slope of the roof
Depth and complexity of the system
Climate and plant selection
Height and accessibility from the ground
Time and cost of labor to install and maintain the roof
Whether elements such as drains, railings, pavers and related items must be installed
A built-in-place, extensive (six inches or shallower) green roof can cost anywhere from $15 to more than $40 per square foot, depending on these and other variables. A modular, extensive green roof system, in which the soil and plant media are placed into preassembled modules in a local nursery and then laid out on top of the existing roof, can reduce these costs to about $9 to $20 per square foot.
These costs are generally offset by the fact that green roofs can double the life cycle of the existing roof. This is because they help moderate the roof’s temperature swings throughout the year. In the heat of summer, a conventional rooftop can approach more than 180° F. In the winter, the same roof can be below freezing. These temperature extremes cause the roof to expand and contract, which eventually causes the roof membrane to crack and need repair and replacement. Additionally, ultraviolet light degrades roof membranes not protected by green roofs.
A green roof can also help reduce energy costs. Scientists at the University of Toronto investigated the environmental impact of a green roof over the expected life of a building. They concluded that a green roof would contribute to a six-percent energy savings in summer, and that the savings could be greater when placed on facilities with a wider rooftop. These savings can also allow a facility to reduce the size of the air-conditioning equipment necessary for the building, another cost savings.
Storm Water Runoff
During heavy rains, especially in large urban areas, even extensive combined sewer systems can become overloaded. This is because a city block can generate as much as nine times the runoff of a woodland area, especially during peak flow periods, according to the U.S. Environmental Protection Agency.
When this happens, sewage treatment facilities become unable to handle the increased flows, and the treatment system for the combined storm water and sanitary sewage is bypassed. This means that the flows go directly to the receiving water body, without treatment. The possible result: water quality problems, including threats to human health, ecosystems and the environment.
Of all the benefits of green roofs, their ability to reduce storm-water runoff is probably the best known. Several studies conducted since the late 1990s have all indicated that this is a significant benefit. In fact, many experts believe that reducing storm water runoff may prove to be the most important economic and environmental benefit of green roofs.
These reports indicate that green roofs can retain as much as 80 percent of the precipitation that falls on them, depending on soil depth and rainfall totals. A study conducted of a modular green roof system of the type discussed earlier found that storm-water runoff can be reduced by as much as 95 percent following a one-in. rainfall. Other studies on storm water runoff include the following.
A Portland, OR, study found that a green roof of two to four inches in soil depth retained 53.5 percent of the precipitation after a rain event. With soil depths of four to five inches, as much as 69 percent of the precipitation was retained.
Various test plots in Chicago indicate that as much as 75 percent of precipitation is retained when a green roof is installed, which reduces peak-flow volumes by as much as 50 percent.
At Penn State University, green roof test plots retained as much as 60 percent of the rainwater. Wayne Community College in Goldsboro, NC, and the Neuseway Nature Study Center in Kinston, NC, have reported similar findings.
Because the benefits of green roofs in reducing storm-water runoff have been proved, more and more cities are adopting regulations that provide an impetus for school administrators and campus facility planners to install these roofs. This alone is helping to make the installation of green roofs economically advantageous. In addition, facility managers can reduce the size of or even eliminate elaborate — and expensive — water-management systems for their buildings, another cost savings.
Leads to LEED
There are other benefits and cost savings that can be attributed to green roofs. For instance, the installation of a green roof can help a facility earn as many as 13 of the 32 points necessary to earn Leadership in Energy and Environmental Design (LEED) certification (see sidebar on pg. XX). College administrators have found that green buildings, especially LEED-certified buildings, can help attract and retain better and more committed staff as well students.
For architects, campus facility planners and school administrators, no single benefit alone may prove to be enough to convince them a green roof is a good investment. But together, the benefits — and savings — definitely add up.
If we look back at mankind’s history, all the major inventions that have been created — automobiles, computers and even the Internet — were developed to serve a need. This holds true for green roofs as well. As we enter an era challenged by global warming and much higher costs for fuel, the value of green roofs will become all the more obvious and continue to grow.
Sandy McCullough is a LEED-accredited professional and a recognized expert on green roofing systems. She can be reached at 312/424-3306 or Sandra.McCullough@WestonSolutions.com.
Green Roofs and LEED Certification
So how, exactly, can a green roof help a facility attain LEED certification? Following are five major categories of the USGBC LEED rating system, along with the potential points that can be earned by installing a green roof.
Reduced Site Disturbance — Potential Rating: 1 point.
Installing a green roof may apply to protecting or restoring the open space consumed by a building’s footprint. The roof also provides a habitat for birds and insects, and promotes biodiversity.
Storm-Water Management — Potential Rating: 1 to 2 points.
As mentioned earlier, green roofs significantly help reduce storm-water discharge. The roofs may also provide storm-water treatment through their ability to remove contaminants and other pollutants.
Heat Island Effect — Potential Rating: 1 point.
Green roofs help reduce rooftop temperatures in summer. When temperatures reach 80° F outside, roof temperatures can climb as high as 180°. This causes a heat island effect in large urban areas, increasing the heat — and the resulting need for air-conditioning.
Water-Efficient Landscaping — Potential Rating: 1 to 2 points.
Green roofs can be designed to require very little irrigation. Drought-resistant plants can be selected, water can be reused and gray-water (waste water that can be used for irrigation) systems can collect excess runoff after storms and use it to water the plants.
Optimize Energy Performance — Potential Rating: 1 to 8 points.
As mentioned earlier, green roofs help reduce energy demand by more than 50 percent in many types of structures. Thus, smaller, less costly cooling systems may be sufficient.