(57) An expandable structure has a core structure (10) which may be expanded on a selected side into a composite structure incorporating the core structure (10) and a contiguous expanded section. The selected sidewall (14) of the core structure (10) rotates up to become the roof of the expanded section. The sidewall (14), endwalls (27A,27B) and floor section (37) of the expanded section are hinged to the frame (200) of the core structure (10) and stacked vertically against the selected sidewall/­roof (14) but do not take up significant floor space within the core section (10). Expansion may be accomplished by power beams (24,23) housed within the roof (16) and subflooring (17) of the core structure (10). The sequence of expansion includes the steps of (a) rotating the selected sidewall/roof (14) to a horizontal position as the roof of the expanded section; (b) driving the sidewall (26) of the expanded section outwardly; (c) driving the endwalls (27A,27B) outwardly; and (d) rotating the floor (37) of the expanded section downwardly to form an extension of the floor (17) of the core section (10).