The Greening of Rooftops

From Mesopotamia to Mount Washington

Legend has it that the Hanging Gardens of Babylon — one of the Seven Wonders of the World —were created by King Nebuchadnezzar in 600 B.C. for his wife, Amyitis. Amyitis, who hailed from a verdant and mountainous land, found the flat, sun-baked, and staid terrain of Mesopotamia depressing, so the king built her an artificial mountain replete with extensive rooftop gardens.

Twenty-six hundred years later, people all over the world are installing green roofs on homes and other buildings for similar reasons. In fact, a recently completed project at the Mount Washington Resort recreating the terrain of the nearby Presidential Range demonstrates that you don’t need tropical temperatures to create a thriving rooftop landscape. Green roofs—if properly designed with plants that can withstand seasonal changes —can be a viable option even for northern New England homeowners.

“Green roofs are a powerful tool in combating the adverse impacts of land development and the loss of open space,”

writes Charles Miller of Roofscapes, Inc., in the Whole Building Design Guide at, which lists their benefits, including controlling stormwater runoff, conserving energy, creating wildlife habitat, and improving the aesthetic environment at both work and home. Also known as eco-roofs, vegetated roof covers, or live roofs, green roofs are living plants installed on top of a flat or sloping roof.

The construction of green roofs relies on a marriage of experts —architects, engineers, builders, horticulturalists, and other specialists—and there are two primary types of green roofs, intensive and extensive. Intensive green roofs are large, typically urban rooftops that often include a promenade, lawn, or largescale planting. Extensive green roofs, writes Miller, “are 6inches or shallower” and are usually found on homes, garages, and outbuildings.

A recently reconstructed boathouse in Essex, Mass., is an example of an extensive green roof.

Nestled amid a sweeping cedar grove and surrounded by spectacular water views, a former boat storage space was transformed into a contemporary yearround dwelling, with a live roof integral to the redesign. The homeowners, who have lived in Asia for many years, are naturalists who will soon retire to the North Shore dwelling.

“It was important to the homeowners to use as many materials from the original boathouse as possible, that the construction be respectful of the environment, and that the home be sustainable,”

says Brian Healy, architect and owner of Healy Architects in Somerville, Mass., adding that not a single cedar was sacrificed during the Essex reconstruction. He explains that the boathouse’s live roof corresponds with the homeowners’ desire for sustainable design.

“A green roof should be incorporated into the landscape and the holistic use of a site, whether urban or rural,”

says Healy.

“It is a philosophical as well as aesthetic endeavor, and not just an appliqué.”

Jeff Licht, owner of Botanicals Nursery, LLC, and a specialist in native plants for green roofs, agrees. Although roof structures are man-made, says Licht, live roofs mimic the environment, bringing an artificial site closer to nature.

For that reason, it is critical that a green roof design and selection of plants complement the surroundings. Licht, who worked with Healy on the Essex home, says that homeowners interested in installing a green roof should also address a major concern—weight—by hiring a structural engineer to determine if an area of a residential roof building can be retrofitted or, in the case of new construction, if adding steel or laminated beams will help to bear the weight of a live roof.

“A new residence with the proper dead load capacity could support a roof garden at a modest cost,”

says Licht. Licht, who has installed both residential and commercial green roofs, points to the Jewell Terrace at the Mount Washington Resort as an example of an intensive green roof that also integrates its surroundings by emulating the hotel’s spectacular mountain backdrop. Completed early this year, the Jewell Terrace is a state-of-the-art green roof above the Presidential Wing that houses the resort’s new Spa and Conference Center.

“The veranda with its view of Mount Washington is one of the resort’s most distinguishing characteristics,”

says the project’s architect, Neil B. Middleton of TRO Jung/Brannen of Boston, who sought to establish an architectural expression that blended with the alpine environment of the Mount Washington Resort.

“It was fortuitous that early glacial formations created an opportunity to build into the hillside instead of building vertically.”

To assist with the landscape design and plant installation, Middleton enlisted the expertise of the Hayter Firm of North Carolina, the hotel’s landscape architect, and Licht, who worked together to imitate the mountain habitat.

“Lou added paths just as you’d see above the tree line, and cairns along trails that lead to the summits of surrounding mountains, and we showcased actual plants that exist as one ascends Mount Washington,”

says Licht. Licht tested numerous species on a makeshift platform at the hotel over the winter of 2007 to determine which plants would survive the rooftop conditions near Mount Washington.

“I did a Noah’s Ark kind of thing with two each of every plant, and all but five species made it,”

he says. With plant viability established, students from Boston and the White Mountains Community College in Berlin, N.H., volunteered to help construct the roof and install approximately 20,000 plants.

Today, the Jewell Terrace features 41 plant species, 15 of which are indigenous to New Hampshire, including Labrador tea, moss campion, three-toothed cinquefoil, bunchberry, alpine bluet, harebell, and White Mountain saxifrage.

Whether to reclaim nature, or to conserve precious resources, green roofs support plant life on areas of buildings heretofore ignored, and the environmental, aesthetic, and psychological benefits cannot be overstated. Recent research by social scientists suggest that everyday encounters with nature —be it a green view of an extensive garden from a second-story office window, or a stroll along a trail on an intensive rooftop in the mountains— restore the ability to concentrate and calm feelings of anxiety.

But it didn’t take a study to tell King Nebuchadnezzar of Babylon that in 600 B.C.; just ask the queen. New Hampshire Public Television recently featured the Jewell Terrace on “Windows to the Wild.”

5 Considerations for Creating a Green Roof

When contemplating an extensive live roof—that is, one which is typically 6 inches or shallower—it is important to  engage  the  combined  expertise  of  engineers, architects,  landscape  designers,  builders,  roofers,  and horticulturalists, and to answer the following questions:
1.What is the intended purpose of the live roof? Is the live roof meant for environmental reasons only, or will you enjoy the area from a window, for example? How you design the live roof, and what plant materials you choose, will likely be influenced by the roof’s use.

2.Is the roof sloped or flat? Flat roofs typically require an additional layer of waterproofing material to drain excess water, while water drains naturally on a sloped roof due to gravity.

3.What is the load, or weight-bearing, capacity of the building structure? If the building is old, can the roof be retrofitted to support the weight of live roof materials, including soil, stones, plants, and substrate materials?

4.Will the roof drainage system manage heavy rain or snowfall and maintain optimum plant growing conditions?

5.What are the appropriate low-maintenance plants for the environment, taking into consideration climate, wind, and irrigation? Is it possible to use native plants?

Rooftop Gardens