Thursday, May 3, 2012

Green Roofs - Old Technology

Green Roofs, Old Technology

A USEPA report entitled “Reducing Urban Heat Islands: Compendium of Strategies” describes the causes and impacts of summertime urban heat islands and promotes strategies for lowering temperatures in U.S. communities. The focus of the strategies is implementing much more-widespread green roofing. A green roof is a vegetation layer grown on a rooftop. Green roof benefits include reduced building energy use, removal of air pollutants by the vegetation, and enhanced stormwater management and water quality control, among others. The report estimates that, for four US urban areas (Salt Lake City, Sacramento, Houston, Chicago), rooftops account for 20-25 percent of the land area. The US Department of Agriculture 2007 National Resources Inventory estimates that there are 111 million acres of developed land in the contiguous 48 states. Applying a conservative (and admittedly, possibly too high) estimate of 20 percent as roof area, and converting to square miles, there may be as much as 34,688 square miles of rooftop in the Lower 48. That’s only slightly more area than the state of Maine (which I personally would not like to see roofed over). This back-of-the-envelope calculation does not account for rooftops in rural areas.
The point is there is tremendous potential for application of green roofing technology.
Thirty US patents use the phrase “green roof$” in the title or abstract (the ‘$’ is a wildcard that includes ‘-s’ and ‘-ing’). Several of these are mining technology, however. 
One of the more recent of these patents is number 7,870,691, “Green roof tile system and methods of use.” Inventors David A. Williams (Austin, TX) and Jonathan W. Kinder (Fort Worth, TX) were issued this patent on January 18, 2011. Classified as 47/65.9, their system is within the broad class of plant husbandry, and found with technologies providing a receptacle for plant growing medium — a walled container in which the container is designed to support a sheet of plants as in a bench or roof top garden. This invention is found within the patentECO Industry Index.
Williams’ and Kinder’s first claim states:
“A green roof tiling system comprising: a tile sheet comprising at least three tiles intended to be disposed above a growing medium layer disposed on a roof; a plurality of detachable bridges connecting adjacent tiles in the tile sheet; a substantially impermeable material included in at least some of the tiles; and a plurality of plant growth channels between adjacent tiles, wherein the plant growth channels include a pathway for water runoff.”
Returning to the USEPA report for a moment, it included the following in a call-out box: “In addition to green roofs, building owners can install green walls, sometimes referred to as living walls or vertical gardens. These walls can involve placing trellises or cables in front of exterior walls and allowing vines to grow up them, or can be more elaborate, with plants actually incorporated into the wall.” The USEPA is somewhat behind the times in recommending this new “living walls” technology. We close with an illustration of the sod home of John and Marget Bakken, Milton, N.D., circa 1895. This photograph was the basis for the U.S. Homestead Act, 1862-1962 commemorative stamp.