Abstract: Substantially rectangular panels are provided with claw engaging means along two opposing edges which are snap engageable within resilient claw ends formed on the opposite side edges of an elongated connector web thus holding the panels in spaced and parallel relationship. If the spacing is relatively wide, then a stiffening panel can be slidably engaged from the ends of the pairs of opposed panels. The web has jaws formed on each side thereof intermediate the ends of the web and the stiffener panel has T-shaped opposing edges slidably engageable with the jaws. The cavities defined by the webs and/or stiffening panels can be insulated by loose fill or by foam.