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Choosing the Right Galvanized Coil Thickness for Your Project

When designing a steel project—whether roofing, ductwork, structural framing, or automotive parts—choosing the right galvanized coil thickness is one of the smartest and most important decisions you will make. Having the right thickness allows your structure to be strong, economical, and able to withstand Canada’s varied weather conditions.

This guide provides comprehensive information on galvanized coil thickness, key factors to evaluate, and how to choose the appropriate option for your project.

What is a Galvanized Coil?

Manufacturers create a galvanized coil by coiling a steel sheet and coating it with a layer of zinc. This zinc layer shields the steel from rust and corrosion, prolonging its life—especially in wet or harsh environments found across Canada, from Alberta’s snow-covered plains to Nova Scotia’s salty sea air.

There are two common galvanization methods: hot-dip and electro-galvanizing.

• Hot-dip galvanizing is achieved through the process of submerging steel in molten zinc, producing a heavy and rough coating for exterior use.
• Electro-galvanizing uses an electrical current to deposit a thin and even coating better suited for applications where surface and smoothness are more important than in heavy corrosion resistance.

What Does Thickness Really Mean?

When we speak of the “thickness” of galvanized steel coils, we are generally speaking of two things:

• The gauge or thickness of the steel base, typically in millimetres or gauges (lower is thicker steel).
• Zinc coating thickness in designations such as G40, G60, or G90. The greater the figure, the greater protection afforded to steel by zinc.

For example, a G90 coating is a measure of about 275 grams of zinc per square meter of steel and offers very good corrosion resistance very handy in outdoor environments like rooftops or metal cladding that is exposed to rain and snow.

Why Coil Thickness Matters

The larger your galvanized coil, the larger the following:

• Structural strength
• Corrosion resistance
• Ease of production
• Price and weight

Go too thin, and the material will distort or fracture under stress. Go too thick, and you might pay for more than you actually need or have fabrication issues. You want to get the right mix of performance, cost, and durability.

Things to Consider while Choosing Thickness

Type of Project

Various applications require various degrees of strength and protection. For less heavy applications intended for indoor usage such as HVAC duct or ceiling tile, you may be able to manage with lighter steel (about 0.7 — 0.9 mm) and a light zinc overcoat. For roofing, exterior panels, or structural framing, however, you will require something more robust—typically between 1.3 and 2.0 mm with a heavier zinc overcoat such as G90 or higher.

Environment and Exposure

In Canada, where winters are cold and summers are rainy, humid, or both, your steel will have to withstand a fluctuation of seasons. Where your application is industrial or coastal, risk of corrosion is greater from air contaminants and salt. In such environments, a heavier gauge of steel with a heavy zinc coating is necessary for long life.

Load-Bearing Requirements

If your steel item has to bear weight e.g., on columns, railings, or beam supports you will have to utilize heavier gauges. This will prevent the material from buckling and bending under load. Galvanized steel used on building construction, for instance, is usually between 1.6 to 2.8 mm thick in order to satisfy structural strength demands.

Ease of Fabrication

Thin steel coils are easier to cut, bend, and shape. So, if your project demands intricate designs, curves, or folds (like automobile parts or household appliances), utilizing 0.7 to 1.2 mm coils may be more convenient. More robust steel, however, may be more costly and may require specialized equipment and more work to produce.

Aesthetic Requirements

If appearance is an issue such as in the case of exposed architectural members then surface finish is critical. Electro-galvanized steel is typically smoother and paintable or coatable. For exposed parts, thinner coils with a finer finish could be best, although they may not be the thickest or strongest.

Common Applications and Their Optimum Thickness Ranges

Let’s go through some examples.

• For indoor ducting of HVAC, not load-bearing and weather-protected either, slender galvanized coils of about 0.7 to 0.9 mm are best. They are lightweight and can be shaped easily.
• If you’re installing commercial or residential roofs, where material is going to be subjected to heavy snow and rain, you’d use coils 1.3 to 1.6 mm thick and a zinc coating such as G90 so that it can last long.
• For wall metal cladding or metal siding, particularly in adverse climatic environments, 1.0 to 1.5 mm thickness is usually adequate. It is a balance between strength and ease of installation without compromising good corrosion resistance.
• When we talk of structural steel framing, for example, in commercial or industrial building, the material must be able to hold considerable weight. In such a situation, your first option would be galvanized coils ranging from 2.0 mm to 2.8 mm in thickness with a good quality zinc coating.
• For automotive parts or metal products that require precise shaping and smooth finish, thinner coils (1.0 to 1.6 mm) with electro-galvanization are normally the preference.
• And for farm equipment or farm structures, which are typically subjected to abrasives, chemicals, and moisture, you’d prefer to employ heavy coils with maximum available zinc coatings.

Cost vs. Performance

Of key concern is cost-effectiveness. Of course, heavier steel and heavier zinc coatings cost more. But if your usage is long-term, subject to the harsh elements, or load-bearing, that little bit of extra cost can pay you back many times over in maintenance and replacement down the line.

Conversely, spec’ing heavy-duty coils when you don’t need them such as putting G90 on office ductwork in an interior office building disproportionately increases your project budget. The trick is to specify only what you absolutely need, regarding use conditions and life cycle.

Inspection and Quality Control

Before choosing a batch or supplier, check the coils for uniform thickness and zinc coating weight. Use mechanical calipers and digital gauges to verify base thickness, and magnetic coating thickness gauges to measure the zinc layer.

Also, search for products that bear certifications to Canadian standards such as CSA or ASTM to ensure they have been tested for corrosion and structural performance.

Availability in Canada The good news is that Canada’s supply chain for galvanized coil is robust. Local mills and suppliers provide a wide range of gauges and coatings, reducing lead times and simplifying quality control. Operating out of Calgary, Toronto, or Vancouver, getting the proper coil to your location isn’t so much an issue. 

Choosing the right galvanized coil thickness isn’t just picking a number—it’s about understanding your project’s needs. Where it’s going to be installed, and how you’re going to be utilizing the steel. If you’re constructing something that must withstand Canada’s cold winters, you will need a heavier coil with more zinc plating. If its indoor use with lower stress, a lower-priced alternative should suffice.

Consider strength, corrosion resistance, formability, cost, and environment to make a smart, long-term decision. The wise decision today will spare you costly repairs, replacement, or failure tomorrow. So slow down, call your supplier, check the specs and build with confidence.