An interest in and demand for building practices that reduce our impact on the environment is producing an integrated, holistic approach to design that incorporates new technologies and living materials on the fifth façade: the roof top.
Aesthetically pleasing, green roofs also function as restorative systems by forming ecological habitats that increase biodiversity. They reduce noise, mitigate heat islands, clean and cool the air, and lower heating and cooling costs.
Green roof technology originated in Germany some 50 years ago as a means of preventing wildfires. According to Jim Mumford, president of GreenScaped Buildings, a green roof wave came through San Diego in the late 1970s, but waterproofing technology wasn't available here at that time, so many of them failed. Mumford said perfected technology didn't come back across the Atlantic until about 12 years ago. Around the time this second wave took hold, the construction industry tanked.
Using improved technology, Mumford installed the county's first green roof in 2007 at his Good Earth Plants facility. Roofs were retrofitted on three buildings and are now green roof test sites. Mumford said sedums, low-growing species commonly used to vegetate green roofs, don't do well in our climate. Native species are also challenging -- only about a third of those planted at the test site have done well.
There are two main categories of green roofs. Extensive green roofs are lightweight systems of drought tolerant self-seeding vegetation with soil depths less than 5 inches. Once established, they require little or no irrigation, fertilizer or maintenance.
"The intent is to turn it loose and have minimal maintenance," said Mumford. "But it doesn't rain enough here. We have to irrigate year round because there's no water retention in 4 inches of soil."
Extensive green roofs can be retrofitted onto existing structures to accommodate the additional weight, but Southern California roofs aren't typically engineered to bear heavy loads, and green roof retrofitting can be expensive.
"If you're designing for a green roof from the get-go, the extra cost is minimal," said Mumford.
Intensive green roofs are elaborately designed roof gardens intended for use and engineered to conform to load requirements. They're installed on relatively flat surfaces with a soil depth of 8 to 12 inches, or as much as 15 feet, depending on load capacity, architectural features and budget. Additional layers like protection boards, water retention mats and maintenance requirements add to the costs of intensive green roofs, but a recent U.S. Government Services Administration research study determined green roofs increase rooftop longevity by 25 to 60 years, effectively doubling the life of any roof.
Studies by Green Roofs for Healthy Cities revealed that the U.S. green roof market grew by 16.1 percent in 2009 and 30 percent in 2010 in spite of a sluggish economy. Much of this growth occurred in cities like Chicago, New York and Washington, D.C., where public policies support green roofs. An estimated 8 million to 9 million square feet of green roofs were installed last year.
The first downtown San Diego eco-roofs built with improved technology appeared in July 2009 on the ninth and 12th floors of Hotel Indigo, downtown's only LEED certified boutique hotel.
Current research points to positive or healing effects greenscaped roofs, gardens and plants have on the people who work or live in these buildings. Multiple studies show viewing plants and nature significantly reduces stress, aids in faster recovery, reduces the use of pain medication and even shortens hospital stays.
Mumford's company installed the 5,000-square-foot green roof atop the main entrance of Sharp Memorial Hospital last December. Visible from the building's upper floors, the design by Glen Schmidt of Schmidt Design Group uses raised planters, trees and groundcover to depict the first few measures of Beethoven's "Ode to Joy."
Landscape architect firm Spurlock Poirier incorporated a healing garden, therapy courtyard, quiet spaces for prayer or meditation, and a 60,000-square-foot extensive green roof at Palomar Pomerado Hospital.
According to Wendy Cohen, director of facilities construction at Palomar Pomerado Hospital, the 1.5-acre green roof teeming with drought tolerant plants is integrated into the building's structural and mechanical performance and stormwater management system. It also increases energy efficiency by reducing the ground reflectance of solar heat gain in the patient tower. The cost of the green roof is about $10 per square foot. Initially it's more expensive than a conventional roof, but a cost analysis determined the hospital would recover the initial cost through energy savings in seven years.
Green roofs often incorporate water retention systems to control storm water run-off, erosion and pollution, critical aspects in designing the replacement lab for the National Oceanic and Atmospheric Administration's Southwest Fisheries Science Center headquarters at UCSD. Proximity to an eroding 200-foot-high coastal bluff forced staff to evacuate two buildings at the current facility and move into temporary quarters. The new lab is being built across from the existing facility on La Jolla Shores Drive. Planned for completion next spring, it incorporates an elaborate stormwater retention system, solar panels and a parking structure green roof planted with California coastal chaparral.
Whether green roofs become a mainstay of San Diego architecture is uncertain. Mumford doubts it will happen without significant public policy support.
Steven Peck, president of the nonprofit Green Roofs for Healthy Cities, makes a case for increased public investment: Adding green roofs to just 1 percent of U.S. buildings would cost $9 billion and create 190,000 labor intensive jobs that can't be exported.