Abstract: A double-skin building panel having an insulating core and having an outer facing sheet laterally offset from and spaced-apart from an inner facing sheet -- each panel presenting an overlapping edge portion along one longitudinal side and an overlapped edge portion along its opposite longitudinal side. The panels are adapted to be erected in lapped relation without externally visible fasteners. The insulating core comprises a honeycomb core member filling a major portion of the space between the facing sheets, and rigid spacing means, one positioned along each side of the panel and thermally insulating the facing sheets from each other. The honeycomb core member presents open ended cells which are substantially entirely filled with an insulating medium, for example, expanded silicate.