Aloft and alive
By Kate Blatt Ancaya on 03/05/2012
A living roof: For many people, it may conjure up images of a character in a children’s story — perhaps the roof equivalent of the marching brooms in Disney’s Fantasia. In reality, a living roof, also known as a green roof, is a simple and accurate description of what is basically a vegetated covering for a roof, with growing medium and plants taking the place of metal, gravel ballast, asphalt shingles or tiles.
Many people are surprised to learn that this is not a new technology fostered by the growing demand for environmentally sound, sustainable solutions. In fact, turf and sod have topped an array of human dwellings for thousands of years, with “contemporary” green roofs probably rooted in Iceland, where sod roofs and walls have been common for hundreds of years, due to a lack of natural resources.
The green-roof industry is still relatively young in the United States but has gained momentum in recent years as more attention is being directed toward examining and utilizing approaches that deliver a positive environmental impact. Much more than simply an aesthetic element, a living roof offers a broad range of advantages for commercial, institutional and residential applications.
In its simplest form, a living roof usually consists of an initial layer of waterproof membrane on which additional layers are built up. A critical component of the initial design process is to assess the weight load the roof can handle and then develop a suitable approach. Careful consideration also is given to the anticipated runoff, which a living roof is ideally suited to control. Finally, the species, textures and colors of the plant material are studied, both to create the desired aesthetics and ensure the health and longevity of the roof.
An ideal example of a recent commercial application is the green roof on the recently completed Dr. Wesley Grant Sr. Southside Center in Asheville, which utilized a traditional built-up system. This project required a waterproof membrane topped with a root barrier, a loose-laid drainage mat, a water-retention mat and 4 inches of growing medium — which was custom mixed to support the selected plants and drain quickly, rather than washing away.
In this case, the plants include a dozen species of drought-tolerant sedums and succulents, involving approximately 10,000 plants. An irrigation system will support growth during the approximately one-year establishment period, after which it will be detached.
A living roof also can be retrofitted to a structure in many circumstances and offer numerous benefits. During its renovation, a federal building in Florence, S.C., received a new roof n that features a sealed membrane and insulation, overlaid with soil housing more than 50,000 plants. Replacement of the existing tar-and-gravel roof with the green roof will substantially reduce heat intrusion into the building’s upper floor by an estimated 60 to 90 percent, which lessens the load on the building’s heating-and-cooling system. Stormwater runoff will be approximately 80 percent less per year due to the controlled absorption of the green roof, which covers roughly 22,000 of the 28,000 total square-foot area.
The new roof system also has a life expectancy of at least 50 years as compared to 20 to 25 years for a standard system, offering sizable replacement savings over time.
While commercial application remains the most common use, architects and homeowners also are electing to include living-roof elements in residential projects. A contemporary home outside Asheville features a number of green technologies, including a geothermal field for heating and cooling. A green roof is located off the main floor of the home on top of the lower guest wing and reaches out to surrounding mountain views (see photo. The green-roof system chosen was a semi-intensive built-up system planted with a variety of native and ornamental perennials and grasses to unify it with the adjacent landscape.
The green roof is accessible to the owner and guests, allowing it to function as an aesthetic garden space.
Living roofs, with benefits
- reduced energy costs, particularly by lessening thermal loading during warm months
- stormwater management by reducing impermeable surface area and retaining 65-100 percent of rainwater
- increased longevity of roof membranes by blocking UV rays and preventing extreme surface temperature fluctuations
- improved air quality, since living roofs gather and absorb pollutants
- reductions in urban heat-island effects by cooling roof surfaces
- contribute to biodiversity by providing wildlife habitat for insects and birds
- added aesthetic quality and increased quality of life
In addition, projects pursuing LEED certification can gain numerous credits by using green-roof solutions.
While the multiple benefits and advantages of green-roof technology are becoming more and more recognized, it’s also important to note that these solutions are not cost-prohibitive and are readily adaptable to a variety of applications. What is required, however, is knowledge and experience to design a living roof that satisfies technological, building, aesthetic and legal requirements, while also implementing a well-conceived solution that ensures long-term sustainability and benefits. An initial feasibility study can determine the best approach, with many architects and engineers now utilizing green-roof experts as consultants in the planning stages of projects.
Proper installation is another critical factor in guaranteeing desired performance, with maintenance important particularly during the establishment stage to promote sustainability over the long term.
As a result, combining desirable aesthetic and lifestyle qualities with improved performance can make a living roof the ideal choice for a project committed to achieving positive environmental objectives.
Kate Blatt Ancaya is co-founder and principal of Living Roofs Inc., an Asheville-based firm. Living Roofs Inc. teams with landscape architects, architects, artists and structural engineers to provide high-quality green-roof systems for commercial, residential and institutional structures, including new construction, retrofits and ongoing maintenance services. More info: livingroofsinc.com.