Metal Roofing Sheets

What metal roofing sheets are used for

Metal roofing sheets are profiled steel or aluminium sheets fixed over purlins to form the roof or wall cladding of a building. They are the standard choice for factories, warehouses, cold storage, poultry sheds and commercial sheds because a single sheet can span several metres, which cuts down on structural steel and speeds up erection.

In the trade the same product gets asked for by several names. Buyers in North India often ask for patra or colour coated patra. Tile profile sheets are usually called kavla roof. All of these describe the sheets on this page.

The four types we supply

Colour coated sheets are galvanised or galvalume steel with a baked paint system on top. This is the most common roofing sheet in industrial work, supplied as PPGI (paint over galvanised) or PPGL (paint over galvalume). We stock JSW, Tata, Essar, AM/NS, Jindal and Prabhat coils, including the branded lines buyers ask for by name such as Durashine, Coloron+, Pragati+, Prisma, Indradhanush and Sabrang.

Bare galvalume sheets carry an aluminium-zinc alloy coating with no paint layer. They are specified where the silver mill finish is acceptable and where coating life matters more than colour. Common trade names are BGL, zincalume, silver sheet, Silveron+ and satin silver. Coating mass is quoted as AZ70 or AZ150, where the number is the grams of alloy per square metre across both surfaces. AZ150 carries roughly twice the coating of AZ70 and is the usual specification for coastal or chemically aggressive sites.

Aluminium sheets do not rust, which makes them suitable for coastal plants, fertiliser units and chemical works where steel corrodes quickly. They are lighter than steel of the same thickness, so the supporting structure can often be lighter too.

Metal tile sheets are pressed into a tile profile to look like a clay tile roof while behaving like a metal one. They are mostly used on farmhouses, resorts, porches and pitched residential roofs.

Choosing a thickness and coating

Two numbers decide most of the cost and most of the performance. The first is base metal thickness, usually between 0.30 mm and 0.80 mm. Thinner sheets cost less and are common on wall cladding and short spans. Thicker sheets resist walking loads and wind uplift better and are the safer choice on wide purlin spacing or exposed sites.

The second is coating mass. For a normal inland industrial building AZ70 is often adequate. Within a few kilometres of the coast, or near a plant that puts acid or ammonia into the air, AZ150 is worth the difference because the coating is what fails first, not the steel.

Paint system matters as well. Standard polyester handles most inland conditions. SMP and PVDF systems hold colour longer under strong sun and are specified where the roof is visible or where the owner wants a longer warranty on fade and chalking.

How long a metal roof lasts

Sheet life depends far more on the coating and the environment than on the profile. A painted galvalume roof inland commonly stays serviceable for well over a decade. The same sheet near salt spray will age faster. Two things shorten life more than anything else: cut edges left unsealed at the eaves, and fasteners that are a lower grade than the sheet. Mixing an ordinary screw with a coated sheet creates a rust point that spreads outward from every fixing.

What to send us when you enquire

The quickest way to a firm price is to send the covered area in square feet or square metres, the span between purlins, the profile you want, the thickness, and the coating or brand if the specification calls for one. If you do not have all of that yet, send the drawing or even a photograph of the existing roof and we will work back from it.

Sheets are rolled to length, so ordering the correct run length avoids site laps. Laps are where most leaks start on an otherwise sound roof.

Accessories are part of the roof

A roofing sheet on its own does not make a weathertight roof. Ridge, flashings, gutters, downtake pipes, barge boards and self-drilling fasteners do the rest of the work, and they need to match the sheet in both coating and colour. These are covered under roofing accessories, and it is worth specifying them at the same time as the sheets so the colours come from the same batch.