2018 ASHS Annual Conference

Concrete houses vastly dominate the architecture on the tropical island of Guam. Although they are exceptionally strong in withstanding typhoon winds, they absorb massive amounts of heat that build up during daylight hours and remain in the building material until the next morning. To escape the heat, air conditioning is frequently used and in many houses the AC units run year round, day and night. Concrete roofs are also sturdy enough to carry a load of growing media (soil) and vegetation. This layer of soil covered by plants may effectively shield the roof from the hot sun. Constructing an extensive (minimal maintenance) type of green roof in the tropics can be relatively easy. The growing medium (soil mixed with gravel and lava) needs to be only 10 cm thick and must be placed on some type of drainage layer. On the university campus, a green roof was established on top of a typical one story residential house. Locally plentiful coconut husks (halved and chopped) were placed on the concrete roof and covered by 10 cm of soil. Commercially recommended synthetic drainage material was also used to compare its efficiency with much lower-cost coconut husks. Research conducted examined irrigation needs, the ability of coconuts to absorb and hold water, time needed to deplete water from organic versus synthetic amended plots, as well as daily fluctuations in concrete roof temperature. It was found that shredded husks were the most effective in storing water and ultimately delaying drought stress during dry periods. There were up to a 15^oC difference in exposed concrete when compared to the concrete covered by soil and vegetation. The type of drainage layer had only a minimal influence on roof temperature. Complete data will be presented and discussed.