Abstract: A building deck structure having sheet metal structural shapes of a box section as sub-purlins, the upper face of the box section having open slots for engaging sheet metal clips which are secured in the box section when the axis of the clip and the box section are about 90.degree. to each other, the clip engaging and holding a formboard-insulation assembly adjacent the top face of the box section and providing a bearing surface for deck supporting shapes for attachment of sheet polymeric structural weather surface to provide uplift resistance to the composite structure. The deck structure of this invention is extremely versatile providing a very economical insulating deck structure which is particularly suited to solar energy absorption and skylights over large areas. The combination structure of this invention permits the use of thinner formboard and lightweight plastic structural weather surface, providing lighter weight insulated and solar energy absorbing decks than previously available.