The Iowa State Capitol, designed by architects John C. Cochrane and Alfred H. Piquenard, was dedicated in 1884 and completed in 1886. The 250,000 square-foot building is largely comprised of sandstone and brick. The original sandstone was from Carroll County, Iowa, and the brown sandstone from Saint Genevieve County, Mo. The brick masonry originated from multiple local sources while the original mortar was Portland based, which is unusual for buildings constructed during this time period. Modified Renaissance in style, the Capitol’s design incorporates rectangular forms, high ceilings and large windows. The roof is commanded by a central towering dome, covered in gold leaf, and surrounded by four smaller, corner-domes. The main dome has steel ribs with brick structure infill. The brick masonry tapers as it ascends from three, two, and then one wythe at the top of the dome. The brick, original to the building, had deteriorated over the years with noted acceleration in 2014 and 2015.
OPN Architects work on the Capitol domes began with a study of the domes’ unique conditions in 2015. The study included exterior investigations to understand the condition and cause of deterioration of the copper skin and masonry. Temperature and humidity monitors were placed throughout the dome; each section was scanned with an infrared camera. The root cause of deterioration was moisture. The immense 275-foot-tall volume lacked an appropriate thermal barrier between the interior and exterior of the space, allowing moisture to travel through the masonry. In addition, there were areas of the upper dome below the lantern that, over time, began to allow bulk water leakage onto the back side of the masonry, further deteriorating the dome.
Following the study, the State of Iowa was able to acquire funding for the project through state appropriations in 2016. Construction began in the spring of 2017, with the project recently completed in the spring of 2019.
2019 • Preservation Iowa Best Public Structure Preservation
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