Glenstone, a museum for post-World War II art outside Washington, D.C., in rural Maryland, is a striking cultural facility, featuring eminent works of outdoor sculpture on a bucolic 200-acre site and exhibitions in a 2006 building designed by Gwathmey Siegel. Now a 170,000-square- foot expansion is under construction, designed by Thomas Phifer and Partners. The scheme, called the Pavilions, is a series of discrete one-room galleries, set around a central water courtyard, with eight of its rooms devoted to—and specifically designed for—the work of a single artist. Among the artists whose work will be on long-term view are Brice Marden, Cy Twombly, Charles Ray, and Michael Heizer (including an outdoor work, Compression Line). The setting of gently rolling hills, with the landscape designed by PWP Landscape Architecture, is an essential part of the visitor experience. Commissioned by collectors Emily Wei Rales and Mitchell Rales, the museum will be completed in 2018. Thomas Phifer spoke about the project with RECORD editor in chief Cathleen McGuigan.

Following are excerpts from their conversation.