An insulated roof deck or wall system which can be used in installing roofs and wall is set forth. The system includes a plurality of metal purlins (10), a plurality of outer panels (2), a plurality of thermal insulation blocks (4), cleats (14), fasteners (12), a first insulation layer (6) and a second insulation layer (7). The metal purlins (10) can form a parallel array of purlins. The outer panels (2) can be attached to the metal purlins (10) in the parallel array. The thermal insulation blocks (4) can be disposed between the metal purlin (10) and the outer panel (2). The cleat (14) can be disposed between the thermal insulation blocks (4) and the outer panel (2) and has a protrusion which is capable of securing the thermal insulation block (4) and inhibits lateral movement between the thermal insulation block (4) and the cleat (14). The first and second insulation layers can be placed on either side of the thermal insulation blocks.