Aluminium Roofing

Aluminium roofing is made from rolled aluminium alloy sheet formed into standing seam panels, corrugated or ribbed sheets, shingles and press-formed tiles. Aluminium does not rust in the way steel does. Aluminium contains no iron, and its surface forms a thin, hard oxide layer that seals the metal and re-forms if scratched, which is why aluminium is widely used on coastal buildings.

Alloys and thickness

Roofing sheet is often a 3000-series alloy such as 3105 or 3003, in a work-hardened temper such as H24. Aluminium is lighter than steel at the same thickness and is usually specified in thousandths of an inch or in millimetres rather than by gauge. Residential roofing typically ranges from about 0.019 in (0.48 mm), used for flashing and some stamped shingles, to about 0.040 in (1.02 mm); standing seam pans are often 0.032 in (0.81 mm) or heavier. Temper and profile geometry (ribs, striations, stamped texture) affect stiffness as much as thickness.

Strengths

• Good corrosion resistance in marine air, where the sacrificial coatings on steel are consumed faster.
• Light weight.
• Recyclable at end of life.

Limitations

• Thermal movement: aluminium expands about 23 x 10^-6 per degree C (about 12.8 x 10^-6 per degree F), roughly twice as much as steel. Panels must be allowed to move, typically with sliding clips; pinning them rigidly pushes the movement into stressed fasteners, noise or waviness.
• Denting: aluminium is less stiff than steel of the same thickness, so thin, flat aluminium dents more easily; thicker sheet and textured or ribbed profiles resist denting.
• Appearance: roofing aluminium is normally factory-painted, usually with a PVDF finish, for colour and UV resistance rather than for corrosion protection.
• Compatibility: aluminium is anodic to copper, stainless steel and carbon steel. It should not be in contact with copper or receive run-off from copper, and fasteners should be compatible (typically stainless or aluminium).

Aluminium systems typically cost more upfront than coated steel and much less than copper.