Exterior, House Building Type, Flat RoofLine, and Prefab Building Type Opting for a lightweight, super stable design that eschews traditional weighty materials, the architects created steel-reinforced panels of expanded polystyrene foam (EPS)to form each of the addition’s seven modular parts. They now top a preexisting concrete garage that the architects had previously converted into a three-bedroom home.  Photo 8 of 10 in Dwell’s Top 10 Prefabs of 2017 from Across the Ocean