Aluminium vs GI Solar Mounting Structures: Which to Choose
Most rooftop solar structures in India are built from either aluminium extrusions or galvanised iron (GI) steel sections. Both can carry panels safely for decades when they are designed and installed correctly — but they behave very differently on a roof. This guide compares the two on the points that matter to EPC contractors and building owners.
Weight and roof load
Aluminium weighs roughly one third as much as steel for the same volume (about 2.7 g/cm³ against 7.85 g/cm³). On a metal-sheet or asbestos roof that was never designed for extra dead load, that difference decides whether a structure can go up without strengthening the roof.
Rail-based aluminium systems such as Mono Rail and Mini Rail mount directly on the roof sheet, so the added load is spread along the crests instead of concentrated on a few legs.
Corrosion resistance
Aluminium protects itself: its surface forms a thin oxide layer that stops further corrosion, and anodising thickens that layer. It does not rust, so cut ends and drilled holes do not become weak points.
GI steel relies on its zinc coating. The coating sacrifices itself over time, and wherever it is cut, drilled or scratched during installation the bare steel underneath can rust unless the damage is treated. Coastal air and industrial pollution shorten the life of the coating.
Whichever metal you choose, fasteners matter. Stainless steel (SS 304) bolts and EPDM rubber between dissimilar metals prevent galvanic corrosion and water ingress at every fixing point.
Installation speed and roof penetrations
Aluminium rails are light enough for one person to carry and cut on site, and rail systems fix to the roof with rivets and EPDM tape or with self-drilling screws into existing holes. Fewer, smaller penetrations mean fewer places for a roof to leak.
GI structures are usually fabricated as frames with legs, which suits ground-mounted and elevated designs but typically needs more fixings into the roof.
Side-by-side comparison
| Factor | Aluminium (6063 T6) | Galvanised iron (GI) |
|---|---|---|
| Weight | About 1/3 of steel | Heavy |
| Corrosion | Self-protecting oxide layer; no rust | Depends on zinc coating; cut edges need treatment |
| Best roofs | Metal sheet, standing seam, asbestos (purlin-mounted) | RCC and ground-mount frames |
| Roof penetrations | Few; rivets, EPDM tape or existing screw holes | Usually more fixing points |
| Maintenance | Minimal | Inspect and touch up the coating |
Which should you choose?
For metal-sheet, standing-seam and asbestos cement roofs — the majority of industrial and commercial rooftops in India — aluminium rail systems are usually the better fit because they add little load, do not rust and need few penetrations.
GI remains common for RCC roofs with elevated frames and for ground-mounted plants, where weight matters less. Either way, ask for the design wind speed, material grade and fastener specification in writing before you order.