Abstract: A composite building panel and method of its construction wherein a preferably rectangular sheet is nailed to wooden strips extending around the sheet perimeter to define a form. A layer of portland cement and sand mortar is spread uniformly over the sheet within the form. A plurality of insulation blocks are applied directly to the wet mortar with uniform spacing between the respective blocks and between the blocks and the wooden strips. Mortar is then spread over the blocks, filling the voids left by such spacing and establishing a covering layer over the blocks. A second sheet is then nailed to the blocks and fasteners extend through the sheets and into the wet mortar grid throughout the panel. Upon hardening the panels are installed by the removal of one or more of the wooden strips so that the projecting margins of the sheets may be lapped with other construction elements to create a secure joint.