Getting a Green Roof

In the Architectural Forum of January 1932, an advertisement announced that 160,000 pounds of 16-ounce Anaconda Copper had been used for the newly opened Kingswood School Cranbrook. There are copper gutters, cornices, louvers, moldings, and chimney covers, but most impressive is the 90,000 square foot batten seam copper roof.

Kingswood Roof Construction Copyright Cranbrook Archives

Workers assembling the roof structure above Unit A, the classroom wing of Kingswood School for Girls. The copper roof behind them is already installed. No barrels of uric acid can be spotted in construction photos. c. 1931. Copyright Cranbrook Archives.

There was just one problem with the new copper roof: it was installed with rolls of bright, new-penny-orange, sheet copper. Eliel Saarinen wanted a green roof, and I think he wanted it quickly.

Yes, he could have waited for the shiny new copper to patinate naturally from rain, humidity, and time. But who has the patience for natural aging when you have an architectural tour de force to complete? Instead, Saarinen turned to chemistry. Using a historic technique common in Europe, the contractor, A. C. Wermuth, directed his workmen to collect their urine in small jars and transfer it to barrels on site. These barrels were then hoisted to the ridge line of the roof, where the pungent catalyst was poured down the copper slope and then spread evenly with brooms.

Science did the rest, and Saarinen got his verdigris color which the Architectural Forum described as a “neutralized complement” to the warm tan brick and buff Mankato stone walls which “harmonized admirably with the heavy foliage of the location.”

Kingswood Early Slide c 1940 Copyright Cranbrook Archives

Color slide of Kingswood School for Girls showing the harmony between landscape, building mass, and materials. c. 1940-1945. Copyright Cranbrook Archives.

The story of more than just rain tinkling on the roof is recorded in Archives as told to former archivist Mark Coir by Dominick Vettraino, who grew up at Cranbrook and served as our landscaper, fireman, superintendent, and jack-of-all-trades. I was asked about the story of peeing-on-the-roof this week by an Upper School chemistry teacher, who’d heard the rumor and is now using it in her lessons for students stuck at home. You, too, can run the experiment: you just need to have a glass, a penny, and be hydrated!

Just like rust develops on iron, patina develops on copper when left exposed to the elements. The copper sulfate on the surface reacts to oxygen in the environment. Unlike rust, the patina actually protects and preserves the copper. However, copper doesn’t turn green quickly: it can take twenty to thirty years for copper to become green! Uric acid can significantly speed up the process. The fact that the Kingswood roof is quite green in early color photos does reinforce the idea that they used a catalyst to age the roof.

The entire copper roof was recycled and replaced in two phases, from 1998 to 2002 and from 2005 to 2007. In the replacement, the copper patination was not accelerated. The fact that the replacement roof is still not green, seventeen to thirteen years on, is to be expected. The roof quickly changed from bright orange to dull brown, and then slowly toward the purplish black you see today. However, I am noticing this spring that when you look at the section of 2002 roof at an acute angle, it’s distinctly turning green at the seams!

05-Cranbrook-Kingswood-School-Copper-Roof-Replacement-HIstorical-Building-Renovations-by-CASS-Detroit-MI-500w

Progress on the new roof. Phase one, completed in 2002, is at the far left and already dull brown. The original (though urethane coated) roof is at right. The new copper roof is shining at the center. May 27, 2006. Courtesy of C.A.S.S. Sheet Metal Specialist, Detroit.

The current color of the roof disappoints many graduates, but in time, it will return to the beautiful green color Saarinen and Wermuth achieved through their very affordable, if not very polite, method. And if you were at Kingswood between 1988 and the new roof replacement: you weren’t seeing a green patina, but a mint-green urethane coating sprayed on the entire roof to (unsuccessfully) slow the leaks!

—Kevin Adkisson, Curatorial Associate

PS: Between the joined “Studio #3” and “Dorm # 2” at the Academy, built in 1932 and 1936 respectively, there is a visible difference between the color of the two copper roofs where the patination has never matched. This can be attributed to different batches of copper. In the new Kingswood roof, every delivery of copper sheeting and copper solder delivered to the site was tested for quality and composition: we wouldn’t want the roof to change color irregularly.

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