Abstract: An insulating panel system, for roof or wall use, includes adjacent insulating panels joined by a connector. The panels include first and second skins adjacent and in contact with opposite faces of an insulating foam core. The first and second skins each terminate in an elongated C-shaped edge. A connector for joining adjacent panels includes an elongated T-shaped channel and an elongated I-shaped channel, for receiving the C-shaped elongated edges of the first and second skins of adjacent panels, and a sheet member joining the T-shaped channel and the I-shaped channel. The foam core is cut away around the C-shaped elongated edges and the remainder of the foam core abuts the sheet member of the connector when the panels are joined. The I-shaped channel and the T-shaped channel each terminates in an elongated lip for retaining the C-shaped elongated edges of the first and second skins. Alternatively both channels may be T-shaped or both channels may be I-shaped.