Aluminum Roofing Specs

Specs

• Aluminum used for roofing must comply with B 209 of the American Society for Testing and Materials, which defines finish, bend properties, stress-corrosion resistance among other factors. The minimum thickness for aluminum in pressformed shingles is 0.019 inches, and for roll-formed panels is 0.024 inches. The material must be naturally corrosion resistant, or if used in an alloy with other metals, have corrosion resistance applied according to ASTM A 463 T2 65 standards.

Shingles

• Aluminum shingles must be applied to a roofing deck that is solid or closely-fitted, unless the shingle is specifically designed for spaced sheathing. The slope of the roof must rise a minimum of three units for every 12 units of horizontal movement, which is a ratio of 3:12. Underlayment, which is a barrier sheet between the shingles and roof deck, is required. If the local climate produces ice along the roof eaves that backs up water, then the underlayment must consist of either two layers cemented together or a self-adhering polymer modified bitumen sheet.

Flashing

• Aluminum shingle roofs require flashing where roofs meet to form valleys. The flashing must be made of aluminum or a metal that meets ASTM standards. It must extend at least 8 inches each way from a centerline, and requires a splash diverter rib that is at least 0.75 inches high at the flow line part of the flashing. Flashing sections require an end lap of over 4 inches. The valley flashing requires a 36-inch wide underlayment running the full length of the flashing directly underneath. This is in addition to underlayment required for all aluminum roofing.

Panels

• Aluminum roofing panels require the same type of roofing deck as aluminum shingles. If they are lapped with nonsoldered seams, the minimum slope is 3:12 without applied lap sealant. With lap sealant that is applied according to approved manufacturer’s instructions, the minimum slope is 1.5:12. For roof systems with standing seams, the minimum slope is 0.25:12, which is nearly flat. In areas with winds above 110 miles per hour, underlayment must be attached with corrosion-resistant fasteners. In areas with winds above 120 mph, the underlayment must be attached with metal or plastic cap nails.