What are the differences and the pros & cons?
By Julianne Calapa, Sheffield Metals
We get a lot of questions about the different types of metal materials that can be used in metal roofing and wall systems. There is one question that comes up more often than others:
“What is the difference between Galvalume® and galvanized metal?”
These two metals, which are technically coatings applied to a steel core, aren’t all that different from one another by definition. However, the benefits and drawbacks of Galvalume and galvanized metal significantly differ, including how long each one lasts, the expectations of how each one will perform, and more.
What is Galvalume?
Definition, Uses, & Comparisons
Bethlehem Steel introduced the Galvalume coating to the construction industry in the early 1970s. Galvalume roofing material combines three of the most important metals used in roofing today — steel, aluminum, and zinc. Manufacturers begin with a carbon steel base sheet that is then continuously hot-dipped with aluminum and zinc alloys until it reaches a coating consisting of 55% aluminum, 43.4% zinc, and 1.6% silicone. This process/product allows for one material to have some of the best characteristics of each metal, which is why it’s become one of the most popular materials in today’s roofing market.
Galvalume may also be referred to as AZ-50 for painted and AZ-55 for unpainted sheet/coil, which refers to the coating weight.
Uses for Galvalume Metal Roofs & Walls
Overall, Galvalume is suitable as a roof, wall, trim, accent, and more in most building applications in some of the most extreme environments, including hurricane zones, locations with high rain or snowfall, high-temperature regions, and more.
Some common uses for Galvalume include:
- Commercial buildings – Hospitals, schools, stores, government buildings, and more
- Residential projects – Single-family, multi-family, condominiums, and more
- Architectural structures – Commercial, governmental, residential, and more
- Structural/industrial applications – Warehouses, factories, and more
- Agricultural – Non-animal confinement spaces, barns, storage, and more
However, there are some situations where Galvalume is NOT recommended for use. In these situations below, the main concern is that the coating will prematurely break down and cause the roof or wall system to fail quicker than if it were not in that location. Here are some circumstances where Galvalume should not be used:
Buildings where animals are confined – Galvalume is not suitable for use on buildings where animals are regularly housed or held. Manure from the animals breaks down into ammonia gas over time and then reacts with the Galvalume coating. This process breaks down the Galvalume coating and leads to degradation of the metal. However, Galvalume is sometimes used on modern chicken houses that are built with a vapor barrier between the chicken area and the roof for appropriate ventilation. It’s best to check with the manufacturer before putting Galvalume on an animal confinement building, as it depends on the design.
In coastal environments – The coating of Galvalume will not stand up to the conditions associated with a coastal environment, including properties up against breaking surfs, large bays, marshes, and other coastlines. Specifically, the large amount of salt (sodium chloride) will harm the Galvalume coating and prematurely degrade the roof or wall system. It’s recommended that properties within a certain distance of a coast use an engineered aluminum roof system, as aluminum resists corrosion and rusting from saltwater for much longer. Plus, aluminum systems still come with a 25-year paint warranty in coastal areas
Advantages / Pros of Galvalume
Warranties – One of the number one selling points of Galvalume is the 25.5 year warranty on the substrate, which may be referred to as a perforation warranty. Galvalume systems also often come with paint and substrate warranties that protect your investment and provide peace of mind that the roof or wall system will last. Plus, commercial property owners have the option to buy a weathertight warranty for their Galvalume roofing structure, which ensures the roof was installed correctly and adheres to strict installation details. (Note: There is not a substrate or paint warranty on Galvalume products within 1,500 feet of saltwater.)
Corrosion resistance– When compared to galvanized metal, Galvalume’s corrosion resistance is about two to four times better. Galvalume’s formula was designed to combine the toughness and strength of zinc with the rust-resistance of aluminum. Research conducted by the Metal Construction Association (MCA) indicates that Galvalume roofing could last as long as 50 to 60+ years without any extreme signs of corrosion.
Self-healing properties – All steel-based products have some degree of edge creep from the exposed steel when the coil is cut, but it can be offset by hemming or touching up exposed edges with paint pens. An advantage of Galvalume that stems from this concept is the fact that it has self-healing characteristics that help control the red rusting at the cut/exposed edges. (Note: A small degree of red rusting at cut edges is normal, but with a Galvalume coating, it will eventually stop.)
Economical – For the most part, Galvalume is reasonably priced and one of the most affordable metal materials available for roofing products. Depending upon the thickness, color, and quality of the desired Galvalume panels, pricing ranges anywhere from $5.00 to $15.00 per square foot.
Disadvantages / Cons of Galvalume
Oil canning – Oil canning is an inherent characteristic of light-gauge, cold-formed metal products, especially products with broad flat areas. It is a visual phenomenon seen as waviness or distortion in the flat surfaces of metal wall and roofing products. Oil canning is only an aesthetic concern that does not affect the strength or performance of the system. This occurrence is a possibility for any kind of metal roofing or walls, including Galvalume. But there are methods to minimize the appearance of oil canning, including:
Hiring an experienced contractor who knows the best material handling practices that help reduce oil canning
Buying trustworthy brands of coil – Using striations or bead stiffeners in the flat area of the panel to minimize the appearance of oil canning
Interactions with Other Materials – Combining different metals on a metal roof system can actually lead to interactions that could result in early degradation, staining, and potential failure of a system altogether. Galvalume performs best when not in contact with copper, bricks, treated lumber, iron, and concrete. If Galvalume is in contact with one of these and is then introduced to an electrolyte, such as water, it can lead to galvanic corrosion of the metal.
What is Galvanized? Definition, Uses, & Comparisons
Galvanized metal products have been around since the 17th century, but the process of “galvanizing” materials became a widespread practice in the early 19th century. Galvanization (or commonly referred to as galvanized) is a protective zinc coating that is applied to a steel or iron substrate through a hot-dip galvanizing process. Before the introduction of Galvalume to the metal roofing industry in the late 20th century, using galvanized sheet and coil was a common practice. However, because of the superior durability and corrosion resistance of Galvalume, 90+ percent of the metal roofing and wall industry in the early 2000s transitioned from galvanized substrates to a Galvalume substrate.
Additionally, galvanized metal sheet/coil may also be called G-90, which refers to the coating weight.
Uses for Galvanized Metal Roofs & Walls
Galvanized metal can be used in the same applications as Galvalume, but the most significant thing to keep in mind is that galvanized is a little more challenging to find. As we mentioned, most manufacturers have stepped toward using Galvalume as the majority of their product offerings because it lasts longer and provides more benefits for property owners.
Like Galvalume, galvanized products are not suited for use on animal enclosures or in coastal environments. In fact, galvanized products will degrade quicker in these environments, as the corrosion resistance is less than Galvalume.
Advantages / Pros of Galvanized
Mid-level price point – Historically, galvanized was generally the cheaper material when compared to Galvalume. However, in the last 20+ years, the pricing of these two materials has fluctuated back and forth. Typical G90 galvanized metal roofing can cost anywhere from $5.00 to $13.00 per square foot and can fluctuate further based on thickness, color, installation costs, location, and more.
Longevity in the right environment – When galvanized metal roofing or wall systems are installed in the right environment, they’ve been known to last decades. It’s recommended that galvanized roofs are used in drier climates where there is not a nearby coastline, an animal enclosure, or significant air pollution. Pooling water, salt spray, animal manure, and air pollution can quickly corrode galvanized metal.
Disadvantages / Cons of Galvanized
No substrate warranties – Arguably the most significant disadvantage to galvanized metal systems is the fact that the substrate doesn’t have a warranty. Most galvanized systems have the potential to be unpredictable in specific environments and uses, meaning that most manufacturers don’t offer warranties on most galvanized products.
Oil canning – Like Galvalume, galvanized metal can also develop oil canning in the flat areas of the panel. To reduce the possibility of oil canning, preventative methods are needed.
Red rust – The zinc coating on galvanized sheet/coil does a good job protecting the steel core for the first decade or so of use. Though once any part of the steel core is exposed, the metal will start to red rust, which is both unsightly and will eat away at the metal over time. Plus, once the red rust starts on a galvanized roof or wall, it will continue to red rust rather quickly.
Not self-healing – As we discussed, all steel products inherently have some degree of “edge creep” near cuts and exposed edges of the panels. The problem with galvanized metal, painted or not, is that once it starts to red rust, it doesn’t eventually stop as Galvalume does. The rust on galvanized will just continue to spread and get worse because it doesn’t have that self-healing property.
Even though Galvalume and galvanized are generally similar in the way they’re created, they have different characteristics that affect how each one should be used in metal roof and wall projects.
Here’s a recap:
A zinc coating hot-dipped onto a steel core with origins dating back to the 17th century.
Often not warrantied due to unpredictability and can develop excessive red rust when core is exposed.
Comes at a similar price point to Galvalume.
An aluminum, zinc, and silicone coating applied to steel core via hot-dipping process.
Often offered with paint, substrate, and weathertight warranty options and has self-healing properties.
Like galvanized products, Galvalume is susceptible to oil canning. RF
[This article, published here as an edited version, was originally published in blog form at www.sheffieldmetals.com/resources/blog)