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Posted by McElroy Metal ● Jan 8, 2021 1:00 PM

How to Choose the Best Metal Roofing Panel

It's no secret that metal roof systems are superior to traditional asphalt shingles. Besides being recyclable and lightweight, longevity and aesthetics are two of the most popular reasons consumers ultimately choose a metal roof system for their home.

But not all metal panels are created equal. Like most other building materials, metal roofing has varying quality and performance levels, which are directly linked to the metal substrate and coating on that panel.

Since your new metal roof's performance, longevity, and appearance depend on the metal substrate and coating selected, let’s take a closer look at these two components that are critical to the long-term curb appeal and performance of any roofing project.

Metal Roofing Panel Materials

In the metal roof industry, the steel substrate consists of a base metal material, illustrated as layer 5 on the drawing below, and applied to the steel base is a corrosion-resistant metallic coating. The corrosion-resistant metallic coating will either be Galvanized or Galvalume®, illustrated as layer 4 on the drawing below.



Galvanized and Galvalume® are the two most popular steel substrates utilized for metal roofing. Click on the above video to learn more.

What is Galvanized or Galvalume?

Galvanized Substrates

The corrosion-resistant metallic coating process is called galvanizing. This process entails applying a zinc metallic coating over the raw steel and is measured by a G-rating, for example, G60 or G100.

The G means the coating is galvanized (zinc), and the numbers refer to the amount of zinc on the surface of the steel sheet.

The amount of zinc applied determines the G-rating assigned to the panel, and there is a direct linear relationship between the amount of zinc and corrosion resistance, so more zinc means more corrosion protection and longer service life.

Let's compare G60 to G100.

  • G60 substrates contain 60 ounces of zinc per 100 square feet of metal panel.
  • G100 substrates contain 100 ounces of zinc for every 100 square feet of metal panel, which means 66% more protective zinc than G60 substrates. 

Currently, McElroy Metal does not offer a G60 panel due to reduced service life, and we strongly recommend G100 as the minimum for your exterior projects.

Galvalume Substrates

Galvanized-G90-Mar-Rural-sizedGalvalume, an alloy of zinc plus aluminum, is the other corrosion-resistant metallic coating option, which can extend the lifespan of your metal roof to 50 years and beyond, with a minimum of component repair or maintenance. 

Galvalume substrates offer the best long-term solution for most applications, and Galvalume's superior performance has been proven in the field. Over four decades of testing has shown that Galvalume delivers superior corrosion resistance compared to Galvalume-Sheet-Mar-Rural-sizedGalvanized panels. In fact, Galvalume's performance in the construction industry has been so superior, that steel mills warranty it against rupture or perforation due to corrosion. Similar steel mill warranties do not exist for Galvanized.

In one test, shown in the photos to the right, unpainted Galvalume and Galvanized panels were placed in four different outdoor environments, including normal marine and a rural setting. The harsher the surroundings, the better Galvalume performed. After 23 years of side-by-side comparison in all areas, Galvalume was two to four times more durable than Galvanized.

Download Our Galvalume Brochure to Find Out More

Paint/Coating Systems For Metal Roofing (The Top Coat)


Due to its constant exposure to the weather and UV rays, selecting the proper coating is just as important as the substrate. The end-user has three popular coating options, Polyester Paint, Silicone Modified Polyester Paint, and Fluoropolymer/PVDF (Kynar 500®), each providing a different protection level against fading and chalking. 

Fading refers to the loss of color saturation caused by long-term exposure to UV rays. 

Chalking refers to the powdery residue left behind as UV rays break down the paint resin/binder over time.

Polyester Paint

Polyester is the cheapest paint option because it also provides the least protection against chalking and fading. When first installed, polyester will look great; but, it will begin to fade and chalk relatively soon after installation.

Due to polyester paints' short lifespan, it should be limited to interior use or basic shade and shelter projects where long-term performance is not required. Therefore, polyester coatings are not recommended for residential metal roofs or post frame buildings.

Silicone Modified Polyester Paint

Sometimes referred to as SMP, this polyester paint performs better due to a 30% silicone content. The added silicone enhances fade and chalk resistance, improving the performance vs. straight polyester coatings. 

Due to the hardness of SMP, micro-fractures can occur during the manufacturing process. These fractures allow direct exposure to the elements, allowing the corrosion process to start. At McElroy Metal, we use Thermoforming technology to reduce the risk of this phenomenon for our Max-Rib panel with SMP coatings. 

Fluoropolymer/PVDF (Kynar 500®)

By using the Kynar 500 resin, this coating option provides superior protection against chalking and fading. (To be classified as a Kynar 500 coating, the PVDF component, Polyvinylidene fluoride, must make up 70% of the total resin content.)

Kynar 500 has been in use since the late 1950s. Although initially developed for high-end projects, you can find Kynar 500 paint systems in use on many pre-engineered buildings, post-frame buildings, and residential roof projects all around the country.

Although Kynar 500 paint systems are nominally more costly than SMP, the enhanced performance easily outweighs the additional expense given that the up-charge for Kynar 500 coatings is often insignificant when you consider the overall cost of a building or metal roofing system.

Learn More About Why You Should Choose Kynar 500® for Your Metal Roof

The substrate and paint system you choose will impact your roof's lifespan and appearance for years to come. Understanding all of the options available allows you to make the best choice possible for protecting your home and your long-term investment in a metal roof.

GALVALUME® is an internationally recognized trademark of BIEC International Inc., and some of its licensed producers.

Kynar 500® is a registered trademark of Arkema Inc.

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Learn everything you need to know about Residential Metal Roofing. Check out our metal roofing resources for inspiration and answers to your questions.

About McElroy Metal

Since 1963, McElroy Metal has served the construction industry with quality products and excellent customer service. The employee-owned components manufacturer is headquartered in Bossier City, La., and has 14 manufacturing facilities across the United States. Quality, service and performance have been the cornerstone of McElroy Metal’s business philosophy and have contributed to the success of the company through the years. As a preferred service provider, these values will continue to be at the forefront of McElroy Metal’s model along with a strong focus on the customer.

Topics: Metal Roofing, Substrates and Coatings

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