Galvanized or Galvalume® for Unpainted Metal Roofing System Applications?

When economics, environment, or certain aesthetics are governing factors for choosing a metal roofing system, an unpainted option may best fit the project. However, overcoming the inherent fear of not using paint as an extra barrier to achieve a desired lifespan may be difficult to overcome.

The good news is that unpainted systems do provide value and have been accepted by the metal roofing market for years. Galvanized and Galvalume® coated steel coils are options to choose from when the decision has been made to go “unpainted” for your project.

Galvanized steel is commonly used in a variety of building products including steel studs and fasteners. Therefore, its use for metal roofing was easily accepted by the building community. Galvanizing as a process, dates back a few hundred years, and involves depositing zinc onto steel coil as the coil is drawn through a molten bath of zinc. Galvalume®, while similar to a galvanized coating in how it is processed, differs by its introduction of aluminum and trace amounts of silicone to the molten bath of zinc. Galvanized steel has a coating with a composition of over 99% zinc, whereas Galvalume® contains 55% aluminum, 43.4% zinc, and 1.6% silicon.

With the presence of aluminum and silicone, Galvalume® offers superior overall performance and lifespan when compared to unpainted galvanized metal roofing panels in most applications. Galvalume® offers significantly greater corrosion resistance, and thus allows metal roof panel manufacturers the ability to offer warranties, which are not normally found with unpainted galvanized metal roof panels.

In one exception, that of animal confinement structures, performance of galvanized exceeds that of Galvalume® metal roof panels. This is due to presence of ammonia gas from animal manure and urine which negatively reacts with Galvalume®, thus greatly reducing its performance.

Generally expected lifespans are about twenty (20) years for unpainted galvanized metal panels, and forty (40) years for unpainted Galvalume® metal panels. Price points for each type fluctuate based upon market conditions, however in most cases they are equal or within a few percentage points of difference.