G90 galvanized steel is one of the most widely used protective metal coatings in North American roofing. Despite its importance, many homeowners and even contractors do not fully understand what the “G90” designation represents, how galvanized coatings work, or why certain thicknesses perform better in harsh climates.

This guide provides a clear, research-based overview of G90 steel, its manufacturing process, and its relevance in Canadian roofing systems.

1. What G90 Means

The designation G90 refers to the weight of zinc coating applied to both sides of a steel sheet during the hot-dip galvanization process.

Standard definition:

G90 = 0.90 ounces of zinc per square foot (total for both sides).

This zinc layer protects the underlying steel from rust and environmental deterioration.

Purpose of the zinc layer

Zinc provides two critical types of protection:

Barrier Protection
A physical shield that prevents air and moisture from reaching the steel surface.
Cathodic Protection
Zinc corrodes first, sacrificing itself to protect the steel beneath.

This dual protection is what makes galvanized steel extremely durable.

2. How G90 Steel Is Manufactured

G90 steel is created using the hot-dip galvanizing method. The process typically includes:

Cleaning the steel sheet
Immersing the steel in molten zinc
Using “air knives” to control coating thickness
Cooling and solidifying the zinc layer
Rolling the material into coils for manufacturing

The hot-dip process ensures uniform coating and strong adhesion, which are essential for roofing performance.

3. G90 vs. Other Galvanized Coating Grades

Galvanized steel is available in several coating weights. The most common include:

Coating Grade	Zinc Weight	Protection Level	Roofing Suitability
G30	0.30 oz/ft²	Low	Not suitable
G60	0.60 oz/ft²	Moderate	Limited use
G90	0.90 oz/ft²	High	Ideal for roofing
G185	1.85 oz/ft²	Very High	Used in extreme environments

Why G90 is standard for roofing

G30 and G60 do not provide enough corrosion resistance in climates with snow, ice, humidity, and salt exposure.
G185 offers superior protection but is heavier and more expensive.

G90 provides the best balance of:

Cost
Weight
Durability
Corrosion resistance

This makes it the preferred grade for residential metal roofing.

4. Performance of G90 Steel in Canadian Climates

Canadian roofing systems face extreme environmental stress:

Repeated freeze–thaw cycles
Heavy snow loads
Strong wind events
Extended moisture exposure
High humidity
UV radiation
Airborne salt from winter roads

G90 steel performs exceptionally well in these conditions due to zinc’s ability to protect steel even when scratched or cut.

Key climate-resistant properties:

Non-absorbent (unlike asphalt)
Resistant to thermal cracking
Maintains strength under snow load
Resists rust even in high-moisture regions
Compatible with protective paint systems (SMP, PVDF)

5. Lifespan of G90 Steel

When properly coated and maintained, G90 steel roofs can last 40–60+ years, depending on:

Paint system
Installation method
Regional conditions
Ventilation beneath the panels
Exposure to salt, moisture, and pollutants

Many manufacturers pair G90 galvanized steel with SMP (Silicone Modified Polyester) Crinkle Finish for increased surface durability and color stability.

6. Common Misunderstandings About G90 Steel

“All galvanized steel is the same.”

Coating thickness varies significantly across grades.

“Paint is the main protection.”

Paint protects appearance; zinc protects the steel itself.

“Scratches cause immediate rust.”

Zinc’s sacrificial protection prevents corrosion at small scratches.

“G60 and G90 perform the same.”

G60 has 33% less zinc, meaning lower corrosion resistance.

7. Where G90 Is Used in Roofing

G90 steel is commonly used in:

Interlocking metal shingles
Standing seam panels
Soffit and fascia components
Metal flashings
Ridge caps
Valley systems
Eaves protection
Wall cladding with high weather exposure

Its structural integrity and corrosion resistance make it ideal for architectural components exposed to Canadian weather.

8. Summary: Why G90 Matters

G90 galvanized steel is a critical roofing material due to:

Proven corrosion protection
Long-term performance
Resistance to harsh climates
Structural strength
Compatibility with modern coatings
Low maintenance needs
Strong longevity performance in freeze–thaw environments

Understanding coating grades helps homeowners and contractors make informed choices about roofing materials, especially in regions with demanding weather patterns.