Is it Easy Being Green? The Costs and Benefits of Green Roofs
Take a look at some of the most exciting, sustainable buildings around the world, and you may notice something they have in common: green roofs, or rooftops covered with a thin layer of soil to allow for grasses and other low-lying plants to grow.
On the outskirts of Austin, Texas, author Chris Brown and his dog Katsu head to the river; the path was once a dumping ground on top of a long-defunct underground oil pipeline. The green roof was conceptualized by John Hart Asher of the Ecosystem Design Group at the Lady Bird Johnson Wildflower Center in Austin.
Green roofs provide major benefits, are relatively straightforward to install, and can be added to existing buildings as well as new construction projects. However, easy installation doesn’t necessarily come cheap: depending on a variety of factors, the costs for installing a green roof can be quite high. Read on as we discuss the many advantages of green roofs and delve into some of the budgeting and cost issues that you might come across if you’re thinking of a living roof for your own home.
Green roofs are aesthetically pleasing and have multiple positive environmental benefits, even if they are small in terms of square footage. Here, a green roof blooms atop the detached garage of a home.
Although green roofs have existed for thousands of years, they’ve become increasingly popular in the past few decades as interest in sustainability has grown. As the largest horizontal surface on a typical building, roofs are vulnerable to both cold and hot temperatures, and other weather conditions. Green roofs help counteract these issues by reducing heat gains in the summer (and therefore saving money on air conditioning), increasing the thermal mass of a building, and acting as insulation during cold winter months. The significant reductions in energy bills based on these factors are usually enough to convince most home owners to install green roofs.
Architect Will Winkelman and landscape architect Todd Richardson collaborated with client JT Bullitt to design a house that blends into its surroundings in Steuben, Maine. The green roof gives the impression that "the ground just jumped onto the roof," Richardson says.
However, the benefits of green roofs go beyond energy savings: their density and depth on a rooftop can provide acoustic insulation, protect the roofing membrane below to increase its lifecycle and longevity (often to more than 50 years, up from the typical 15 years), and help earn points towards LEED certification. In fact, according to the Michigan–based network of green roof professionals LiveRoof, the biggest financial benefit of a green roof isn’t money saved on electrical bills, but rather not having to replace and regularly maintain a roof. Because green roofs extend the lifetime of a roof between 200 and 300 percent, owners are able to save significant costs in the long run.
At a net-zero home in San Francisco, the house's green roof is more of a brown roof: a desert-like array of native and non-native succulents that require minimal irrigation. The soil area is maintained with motorcycle tires (including one from a Harley hog), which control erosion. Composting takes place here as well.
For the broader community, green roofs are aesthetically pleasing, adding a bit of greenery to what is often an otherwise gray or black cityscape. They also add to urban biodiversity and typically use local plants that are native to the area. Most companies, like Portland, Oregon–based Columbia Green Technologies, select plants that are "drought tolerant and appropriate for the depth of the system and project climate."
The green roof on New York’s Javits Center, designed by FXFOWLE, is the second-largest green roof in the country. The green roof prevents approximately 6.8 million gallons of stormwater run-off annually.
Other community benefits include reduction of stormwater runoff that would often go into overflowing municipal systems, and improvements to air quality; the living roof actively absorbs many pollutants and passively filters and directs airflows. Because green roofs tend to absorb radiation from the sun rather than reflect it onto its neighbors, green roofs also mitigate the heat island effect in cities.
At a home by Richard Brown Architect, the site's slope is turned into various terraces, which allows the roof of the garage to function as a green roof accessible from a side yard entry.
However, all of these environmental, community, economic, and aesthetic benefits come at a cost. This can depend on a wide range of factors including the type of roof system used, where the building is located, the availability of a labor force that is experienced in green roof installation and maintenance, and the need for additional structural support.
Purple thistles, California poppies, clover, and dandelions have all taken root in the roughly 10-inch-deep, lightweight humus and grape-husk soil in this 580-square-foot green roof. Designer Peter Liang says that he "wanted to plant a green roof for its thermal mass, but I wanted it to be as natural as possible."
Today, green roofs comes in two primary forms: intensive (which can hold up to 150 pounds per square foot and typically support more diverse types of plants—but also requires more maintenance), and extensive (able to support up to 25 pounds of vegetation per square foot and usually grown naturally and without restriction, needing only yearly weeding and fertilization). These two systems are significantly different in their weight, and therefore also associated costs with construction, installation, and maintenance.
In an industrial neighborhood in Brooklyn, a verdant green roof of native grasses, wildflowers, and fruits creates an oasis.
Factors like location, quality of the roofing membrane, roof accessibility, structural load capacity, and ease of material conveyance to the roof affect the price, explains Recover Green Roofs, a Boston area–based design-build firm specializing rooftop gardens and green roofs in New England. Based on these considerations, Recover Green Roofs has found that extensive roofs can cost about $10 to $50 per square foot, while intensive roofs can cost from $20 to $200+ per square foot.
"In this project, we got so much benefit out of this 'secret garden' for the master suite along with all of these environmental benefits that the residents were excited to embrace. It's one of the pieces we are happiest about," says architect Jonathan Feldman.
Baltimore, Maryland–based Green Roof Technology, a company that specializes in the specification and design of green roofs, notes that increases in costs can also depend on growing media depth, desired water storage, and plant material. However, they point out that green roofs can be considerably less expensive—up to 50% cheaper—when they cover more than 10,000 square feet because of economies of scale.
Villa Bio is situated a little over an hour outside of Barcelona in Llers, a green, hilly, sun-bathed sprawl near Figueres (hometown of everyone’s favorite mustachioed surrealist, Salvador Dali). The hydroponic rooftop garden grows out of volcanic stones. The home is conceived as a giant C-shaped spiral.
Interested in installing a green roof but want to do your own research before reaching out to a professional or consultant? You’re in luck: in 2010, the University of Arizona put together a handy calculator tool that allows you to calculate the annual energy performance of a building with a vegetative green roof compared to a traditional dark or white roof. More helpful resources including design standards, conference recordings, and an open forum webinar can also be found on the Green Roofs for Health Cities website.
Stained cedar, ipe, and concrete form the palette of this modern, verdant 2,500-square-foot home in Kansas City. Indigenous wildflowers and native grasses grow on top of the structure; this planted roof also helps insulate the home and limited its energy needs.
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