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Restoring the U.S. Capitol Dome

Cast Iron: An Innovative Material in 1850, A Repair Nightmare in 2010

Since its completion in the 1850s, the U.S. Capitol Dome has undergone changes in the way cast iron components fit together. Heating and cooling modernization, successive painting programs, and corrosion due to water infiltration have conspired to make cast iron plates more rigid and less able to accommodate movement than when initially assembled.  Repairing these cracks, and preventing new ones, required innovative technology. Unlike other metals, cast iron cannot be welded, making rehabilitation especially challenging. The induced heat of welding causes changes in the material’s cellular structure. To restore structural integrity while allowing for movement during thermal cycles, the project team tested a variety of cast iron repair methods before selecting a mechanical stitching technique.

The presentation will explore the history and challenges of the Capitol Dome project, review fundamentals of cast iron repair, and share best practices learned from this pioneering landmark restoration.

Presenter Name: Richard P. Kadlubowski, AIA

Presenter Bio: Since 1990, Richard has been instrumental on Hoffmann Architect’s team for the restoration of the Dome of the U.S. Capitol, a project that spanned over 20 years and included comprehensive evaluation and documentation of deficiencies, exhaustive testing of materials and methods, and master planning.  During the construction portions of the project, he has provided oversight of the ambitious repair work. He has also provided building envelope assessment and design services for other noteworthy institutions, including the Library of Congress, the Smithsonian Institution, and the Folger Shakespeare Library. He has been with Hoffmann Architects for more than 30 years.

Presented by: AIA|DC Public Architects Committee


After attending the course, participants will be able to:

  • Evaluate and explore cast iron repair methods to select the most effective restoration strategy;

  • Describe and identify material properties that may limit repair options;

  • Explore historical records and methodologies to determine which repair approach would best maintain the structure’s original character; and

  • Explain logistical challenges to an extensive restoration of a continuously occupied, prominent building.