Specifications: Inside curb to curb measurement of 36″ x 30″. Material: Cover and frame are 11 gauge (2.3 mm) aluminum. Cover: Brake-formed, hollow-metal design with 3″ (75 mm) concealed polyisocyanurate insulation (R Value of 20+), 5″ (100 mm) beaded, overlapping flange, fully welded at corners, and internally reinforced for 40 psf