Abstract: Pre-fabricated modular panels for attachment to the exterior walls of existing buildings to provide supplementary insulation. The panels include exterior facing, vertical support ribs, spacer members, a fastening strip secured to the spacer members and compressible insulation mounted from the vertical ribs to provide a ventilation space between the insulation and the facing. When the fastening strip is fastened to the building exterior wall, the insulation contacts said wall and is compressed thereagainst in contour accommodating relationship.