Old concept becoming new strategy for green building
Amid a sea of asphalt and concrete in a commercial area of Kearny Mesa, Jim Mumford is cultivating an island of green. However, you won’t see his horticultural efforts as you drive past his company location – unless you’re looking up. When Mumford gardens, he climbs onto the roof.
Mumford and his Greenscaped Buildings associates, Ulf Waldmann and Robert Thiele, presented a free, green roofs workshop at CCSE recently to an audience of landscapers, building contractors, architects and others eager to learn how green roof designs, originated by medieval Vikings, are coming into the mainstream as a way to bring environmental health back to urban communities. Sporting a green roof is commonplace throughout much of Europe, but the idea is just catching on in the United States.
The traditional Scandinavian green roofs were made of sod or turf, but today the vegetation varies from succulents and fescues to fruits and vegetables. Some green roof advantages are fairly obvious – reduced energy needs for interior heating and cooling, increased carbon dioxide absorption and improved aesthetics.
Other benefits can be just as significant, Mumford pointed out, such as controlling stormwater runoff and pollution, creating wildlife habitats, reducing sound and mitigating urban heat-island effects – the tendency of cities to be warmer than the surrounding region. According to the Environmental Protection Agency, on a hot, sunny summer day, the sun can heat rooftops 50 to 90 degrees hotter than ambient temperatures, elevating air pollution and compromising human health. Studies of green roofs have shown that if all the roofs in a major city were "greened," urban temperatures could be reduced by as much as 12 degrees (F).
Another advantage of green roofs is extended life expectancy – a green roof can double or triple the life of the underlying conventional roof by protecting it from debris, shielding it from UV radiation and buffering temperature extremes.
Mumford explained that green roofs generally fall into two categories: extensive and intensive. Extensive green roofs are established on a thin layer of growing medium from 1-1/2 to 6 inches thick, planted with sod or ground cover plants and usually only accessed for maintenance. Intensive green roofs, with a thicker soil base, are more like gardens with easy access and may include any plant from herbs to shrubs and small trees. Both mean a commitment to care and maintenance, with extensive plantings needing only occasional weeding and little watering, while intensive gardens require irrigation, feeding and frequent care.
The three main areas of concern when contemplating a green roof are structural integrity, waterproofing and plant sustainability. First, the home or building must have the structural strength to support the superimposed weight resulting from a landscaped roof, taking into consideration times when it is saturated. Then, as with all roofs, long-term waterproofing is necessary. With the escalation of European green roofs, advances have been made in membranes that not only seal the underlying roof deck, but also form a root barrier. Finally, as for the plants, there are nearly endless possibilities, but for reduced costs and less frequent maintenance, low-growing plants are preferable.
Green roofs are becoming common in Chicago, Atlanta and Portland, where builders are encouraged to use living roofs by fee reductions and other incentives. While the cost of a green roof may run two or three times more than a conventional roof, it’s likely to be cheaper in the long run because of energy savings and extended roof life. Above all, Mumford said, green roofs provide significant social and environmental benefits, “bringing health back to urban communities and capturing the spirit of sustainability.”
Other links:
Green Roofs for Healthy Cities
Chicago City Hall – Nation’s first municipal green roof
California Academy of Sciences, San Francisco – Unusual extensive green roof
A dripping faucet waste 15-21 gallons per day
