Since the Jefferson Memorial’s completion in 1943, visitors have admired its pristine white marble dome. But in the past few years, biofilm and dirt had covered much of the John Russell Pope–designed building—especially the dome—and the roof was leaking. Working with the National Park Service, GWWO Architects oversaw an intensive cleaning and roof restoration project that wrapped up in September of 2021.

“Resolving how to remove the biofilm was the most challenging part of the project,” says architect and GWWO principal John Gregg. He and his colleagues, along with contractor Grunley Construction Company and conservator Building Conservation Associates, settled on a combination of steam and laser cleaning. They tackled other grime with methods including micro-abrasion, applying gentle detergents, and “elbow grease and warm water,” says Gregg.

They also replaced the failing original waterproofing system with a new one, as well as repointing much of the marble and limestone on the memorial’s exterior. Now the team has started on a second phase of work—slated for completion in late 2023—that includes updating the site’s accessibility and visitor services areas.