Bermuda Stepped Roofs and Cisterns: John Gardner and the Possibility of Architectural Transformation as a Tool for Water Supply

Guest post by: Melina Sempill Watts

In Bermuda, the islands are sprinkled by buildings that look like cakes topped by white frosting.  The aesthetic enchantment is incidental because at heart, these stepped white limestone roofs and cistern pairings are built to capture rainwater for domestic use. Consider that Bermuda has 181 islands, over 71,000 people, half a million tourists per year and no major natural water sources.  For over 400 years, it is these fairy-tale pretty white stepped roofs that have made on island human life possible.

Architect / artist John Gardner has been designing buildings featuring stepped roof/ cistern pairings for his whole career, as his father, who co-founded Cooper Gardner, did before him.  When the North Santa Monica Bay Watershed Community, a project of Safe, Clean Water L.A., reached out to Gardner about the feasibility of creating a demonstration project replicating these beautiful and hard-working roof/cistern pairings in Southern California, Gardner was intrigued.

Image by: John Gardner

From the onset of the conversation, Gardner understood that living in a house with a cistern might sound like a tenuous answer to water supply needs for people on the mainland accustomed to the consistency of municipal water supply. However, math is on the side of the cistern: an inch of rainfall on a square foot of surface area yields .623 gallons. Thus a 2,000 foot home captures 1,246 gallons per each 1” inch rainfall event. In Bermuda, with an average rainfall of 55” inches per year, this brings the amount of available water for those living in a 2000’ home to about 68,530 gallons per year. Divide that by 365 days per year and this theoretical household is living on about 188 gallons of water a day.  Can rainwater capture from roofs and cisterns work in rain-limited locations?

Currently there is an (unenforced) mandate that each person in California use 55 gallons of water a day. The 188 gallons from the potential home in Bermuda comes to 47 gallons per person for a family of four. As a comparison, imagine a potential project in Topanga, an unincorporated city in Los Angeles County, where the average square foot of a home sold last month was 2,716 square feet. Given an average annual rainfall of 19.4 inches, that could come out to 52,690 gallons a year, or 144 gallons per day…enough for a theoretical family of three.  While there are many houses smaller than this and multiple- family units are a totally different animal, there are many homes, businesses, schools and municipal buildings in L.A. County (and beyond) that could benefit from a Bermuda roof and cistern retrofit.

Image by: John Gardner

Gardner explains, “In the Bermuda context, the purpose is to catch as much rainwater as you can and hold it safely for your use as there is no real alternative that is accessible on a residential level historically. The alternatives are to drill a well, which is not always potable or to use an RO (reverse osmosis) plant which is not really practical unless you’re by the sea or to be on a municipal system, which is not that good.”  Bermudians understand the vulnerability of their own residential water supply so in drought conditions, “We modify our behavior accordingly: when there is a drought, we use less water. It’s the culture to use water this way.”

Gardner comments that Bermuda roofs are “said to slow [rainwater] with the steps on the roof. The construction includes 1” inch thick roofs that connect in vertical edges, unlike the eaves under roofs in other countries, that then funnel the water directly into pipes that feed into the cistern.”  Cisterns are covered, preventing propagation of mosquito larvae and dark, barring algae growth, while air ventilation prevents stagnation. Gardner adds wryly, ““One accepts that  dirt gets on the roof, blown dirt, bird poop. The tank is still, so sediment falls to the bottom.” Nowadays, most people filter the water prior to drinking.  Cisterns have to be cleaned on a regular basis, ideally every 2 years, often closer to every 5 years.

Image by: John Gardner

When asked about construction Gardner clarified that the traditional limestone roofs are historical now, as Bermuda has chosen to limit removal of limestone from quarries for conservation purposes. “Nowadays slate is in common use, as are non-stone product like SKB and others, including glass fiber reinforced concrete board, foam profile on top, finished with polymer, painted white with latex paint.” Historically, builders “made lime in kilns, slaking that on roofs and it came white. That’s where the white roof started. A white roof does not have the same heat build-up.” Conversely, he adds, “Tar or paper roofs which are dark grey or black, cause the need to fight heat gain”. Using the color white to create cooler interiors is a powerful tool to help reduce climate change impacts.

Construction requires expertise in building stepped roofs, Gardner adds, “The eave detail is critical as is spacing of rafters to provide support for the roof and the weight of rainwater. Builders need to be sure that the board is strong enough and set nails properly.  I would be careful of the substrate, and paint it white.”  Gardner emphasized that there is a maintenance issue, roofs which can become mildewy if unattended. “Property owners have to clean the roofs every two years. The taste of the water becomes a natural litmus test whether roof is clean or not.” In Bermuda many homeowners paint their own roofs and Gardner talks fondly about how the new paint goes on “soft, like a cake.”

Image by: John Gardner

Using cisterns to store drinking quality water could be a bit of a mind-binder for public health officials in California and elsewhere. Gardner explains that Bermuda is using “a modified universal building code, … dealing with water codes. Everything goes back to two laws in 1949 and 1951 which are the regulations about how you collect and store water.” When asked about the certification process, Gardner explained that construction workers know how to make these roofs, “It is a culturally standard practice, we don’t really need to draw it out. Everyone knows how to build it. Finished roofs are inspected by the health department.”

Bermuda is way ahead on climate change action, creating sustainable energy and managing climate change inputs by going solar. Architects have created a process to lay in photovoltaics, made of glass and metal, a few inches above the top of a Bermuda roof. The gaps allow the rain to funnel down on to the classic roof underneath.

Gardner’s architecture is informed both by his work as an artist and an impulse towards community-making. Wanting a space for art in Bermuda, Gardner was integral to the creation of the Bermuda National Gallery. Gardner’s painting Hurricane Watching grew out of a family excursion. “I did that piece for my daughters who were younger at the time, we’d always gone down to south shore when the surf is booming.  I went down and watched. Watching the ocean being absolutely wild, very close to you is quite an experience. You hope it doesn’t do a lot of damage and sometimes it does.  Going to watch is kind of a cultural thing.  It touches at the heart of a very Bermudian experience, which is hurricane watching.” Other work includes Triangle,which plays with the dread conjured by the idea of the Bermuda Triangle, while After The Party – 400 Cakes is a wall of actual cakes whose white icing evokes … the white roofs of Bermuda.

Architect / artist John Gardner will join the  North Santa Monica Bay Watershed Community  on the evening of September 23, 2021 from 5:30 -7:30 p.m.; he will be scheduled to go on at approximately 6:30 PST. Contact watershed coordinator at for the Zoom link.


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