GI vs Galvalume Roofing Sheets: Thickness & Price Guide

Buying roofing sheets for a shed, warehouse or commercial building? Comparing only colour and price per piece can be misleading. Understand the steel base, protective coating, paint finish and dimensions before comparing quotations.

CR Base, GI and Galvalume: What Is the Difference?

CR means cold-rolled steel. It describes the steel substrate or processing route, not the complete protective coating system. A galvanized sheet can also have a cold-rolled steel substrate.

If a quotation says “CR-base colour-coated sheet”, ask whether the steel has a zinc or aluminium-zinc metallic coating beneath the paint. Confirm the complete manufacturer specification.

GI or galvanized steel has a zinc coating over the steel. Galvalume-type steel has an aluminium-zinc alloy coating. Compare the coating designation, coating mass, steel grade and suitability for your installation environment.

Pre-Painted vs Bare Roofing Sheets

“Pre-painted” describes a factory-applied paint finish. “Bare” generally means there is no decorative paint finish; it does not necessarily mean the steel has no metallic protection.

• Bare GI: Zinc-coated steel without a decorative paint finish.
• PPGI: Pre-painted galvanized steel.
• Bare Galvalume: Aluminium-zinc alloy-coated steel without a decorative paint finish.
• PPGL: Pre-painted aluminium-zinc alloy-coated steel.

Bare Galvalume and uncoated bare CR steel are different materials. Ask the supplier to write the complete description on the quotation.

Roofing Sheet Thickness: BMT vs TCT

A quotation stating only “0.50 mm sheet” is incomplete unless the thickness basis is clear.

• BMT — Base Metal Thickness: Thickness of the steel base, excluding coatings.
• TCT — Total Coated Thickness: Thickness including the coatings.

A 0.50 mm TCT sheet should not be treated as equivalent to a 0.50 mm BMT sheet. Check the manufacturer-declared thickness basis and tolerances.

Thickness alone does not determine roof load capacity. Profile geometry, steel grade, support spacing, fasteners and design loads must also be considered. Follow the applicable manufacturer guidance and project design.

How Sheet Length and Width Affect Cost

Two sheets of the same thickness can have different per-piece prices because their lengths or widths differ.

• Overall width: The full physical sheet width.
• Effective cover width: The usable coverage after the specified side overlap.

For example, a sheet 3 metres long with 1 metre effective cover width provides a nominal 3 square metres of coverage before allowing for end laps and other project requirements. This is an illustrative calculation, not a product specification.

Longer sheets may reduce end joints in some layouts. However, transport access, lifting, handling and roof design must also be checked.

Why Do Roofing Sheet Prices Differ?

There is no universal rule that Galvalume always costs a fixed amount more than GI, or that every colour-coated sheet has the same quality.

Price depends on:

• Base metal thickness and steel grade.
• Metallic coating type and coating mass.
• Paint system, colour and finish.
• Profile, sheet length and effective cover width.
• Brand, quantity and processing.
• GST, freight, unloading and accessories.

Painting adds a processing cost to the underlying material. However, actual quotations may differ because thickness, coatings, grades and commercial terms also vary.

Compare equivalent specifications and cost per effective covered area—not just price per piece or per kg. Confirm current rates before ordering.

Frequently Asked Questions

Is every colour-coated sheet Galvalume?

No. Colour-coated sheets may use galvanized steel or aluminium-zinc alloy-coated steel. Ask whether the quoted product is PPGI or PPGL.

Does CR base mean there is no zinc coating?

No. Cold-rolled steel can be the substrate beneath a metallic coating. Check the complete product specification.

Does bare mean there is no corrosion-protection coating?

Not necessarily. Bare GI and bare Galvalume can retain their metallic coatings while having no decorative paint finish.

Which is cheaper: GI, Galvalume, PPGI or PPGL?

There is no fixed price order across all products. Compare equivalent thickness, grade, coating mass, dimensions and commercial terms.

Can I compare 0.47 mm and 0.50 mm sheets directly?

First confirm whether both thicknesses are BMT or TCT. Then compare the remaining specifications and project requirements.

Is a longer roofing sheet always better?

No. The