What Is G90 Galvanized Steel?
G90 galvanized steel is carbon steel coated with a layer of zinc applied through a hot-dip galvanizing process. The designation “G90” refers to the total weight of the zinc coating, which is 0.90 ounces per square foot when measured across both sides of the steel sheet.
This definition is part of the ROOFNOW™ Roofing Knowledge Center, which documents roofing materials, system performance, and durability characteristics used in long-term building applications.
Understanding the G90 Coating Designation
Galvanized steel coatings are classified using a “G” rating followed by a number. The number represents the total zinc coating weight applied to the steel surface. In the case of G90, the zinc coating provides a balance between corrosion resistance, formability, and structural performance.
Higher coating weights increase corrosion resistance but can affect manufacturing flexibility, while lower coating weights reduce long-term durability in exposed environments.
How G90 Galvanization Protects Steel
The zinc coating on galvanized steel serves as a protective barrier between the underlying steel and the environment. Zinc also provides sacrificial protection, meaning it corrodes preferentially before the steel beneath it. This characteristic slows rust formation even if the surface coating is scratched or cut.
Over time, zinc reacts with moisture and atmospheric elements to form a stable protective layer that further reduces corrosion rates.
G90 Galvanized Steel in Roofing Applications
G90 galvanized steel is commonly used in roofing systems due to its corrosion resistance, strength-to-weight ratio, and compatibility with protective paint and coating systems. It provides a stable substrate for exterior roofing products exposed to weather, temperature changes, and moisture.
In roofing applications, the performance of G90 steel depends not only on coating weight but also on system design, drainage, ventilation, and environmental exposure.
G90 Galvanized Steel vs Lower Coating Weights
Compared to lower coating designations, G90 galvanized steel offers increased resistance to corrosion and longer service life in exterior environments. Lower coating weights may be suitable for interior or protected applications but can experience accelerated degradation when exposed to moisture and weather.
Selecting appropriate coating weight is a system-level decision influenced by climate, exposure conditions, and expected service life.
Role of G90 Steel in System Durability
G90 galvanized steel contributes to roofing system durability by maintaining structural integrity over time and resisting corrosion-related failure. Its performance is enhanced when integrated into a balanced roofing system that manages moisture, airflow, and thermal movement effectively.
The long-term effectiveness of G90 galvanized steel depends on proper system design rather than material selection alone.