Background: Despite an idyllic location in the Caribbean, the island of Bermuda and its 60,000 inhabitants face two stark environmental challenges. First, with scarce and difficult to access groundwater resources, fresh water drinking supplies have posed a challenge to development since colonial times. Secondly, the island is annually battered by hurricanes, whose strong winds can tear houses apart.
Program: An elegant solution to both these problems evolved 400 years ago with the first colonizers. Rainwater harvesting was a clear necessity for residents; but the innovation came when rainwater catchment technology was integrated with stronger construction. Exploiting the island’s abundant limestone resources, Bermudians built special roofs out of the stone slabs that catch rainwater and double as sturdy barriers against winds. The roofs are terraced, slowing down rainwater and directing it to gutters, which in turn feed into underground storage tanks. The white color of the roofs also helps disinfect surfaces and water by reflecting UV light. Furthermore, the roofs are oriented so as to minimize the potential of roof uplift during storms.
Building codes require residents to convert at least 80% of their roof’s surface into a catchment area. The catchment system is nearly self-sufficient: one figure puts the total annual volume collected as roughly equivalent to four swimming pools per household (see video under ‘More Information’). Today drinking water supply is supplemented through desalinization and pumping from thin underground lenses of freshwater that sit atop seawater. Though exact numbers regarding the percentage of total demand met by each source vary, the system provides households most of the water they need throughout the year (about 30 gallons per day).
The roofs have an impressive resilience to storms; one of the original roofs installed in 1640 atop the Carter House remains intact.
Constraints: Some constraints exist that limit transferability of the product. The local supply of limestone has been exhausted, requiring imports and substitute materials; the wooded support beams must also be imported. The source and quality of the materials and complexity of design and construction significantly add to the cost, making it more expensive than basic roof designs. The tank’s and roofs require more vigilance than a centralized supply: roofs must be cleaned regularly to avoid the contamination of rainwater with by animal and plant matter. Cisterns likewise must be monitored regularly for bacterial growth and the presence of animals like salamanders. Finally, rainwater alone is not enough to meet needs during peak tourist season, when demand outstrips supply by about 20%.
Bandon, Alexandra. “This roof Resists Hurricanes, Collects Water.” This Old House Magazine. http://www.thisoldhouse.com/toh/article/0,,636457,00.html
Discovery Channel Canada. ‘Bermuda’s Water Catchment System.’ Video posted 6 July 2010. [URL at bottom of page]
Innovative Building Systems (Bahamas), Ltd. http://www.thebermudaroof.com/
Forbes, Keith A. “Bermuda’s Architecture.” Bermuda Online. 3 November 2012. http://www.bermuda-online.org/architecture.htm
In-depth look at construction and operation of Bermuda roofs: http://www.youtube.com/watch?v=uicDtLdOG4o
Photos Courtesy: Charles Anderson [banner photo], Keith Forbes [center photo]