A prefabricated building wall is particularly suited for residences. The wall has a metal outer frame, and inner frames of metal may be located therein for doors and windows. Non-metallic stiffening members are interconnected within the outer frame in a diagonal grid. Hardenable plastic foam is injected into the frame to serve as insulation and support. The stiffening members are I-beams with apertures along their webs to allow them to be interlaced.