Metals and Finishes: 2 Critical Things Most Contractors Don’t Know About Metal Roofing

Here’s a special post from Todd Miller.

I am starting a new series about 10 critical things that roofing contractors often don’t know about metal roofing. In my 35 years of answering questions from homeowners and contractors about metal roofing, these 10 things come up over, and over. Unfortunately, I often hear stories of homeowners who had metal roofs installed but in the end, were upset and frustrated with a roof that did not perform as they expected.

When I dig into these situations, I often find critical considerations particular to metal roofing that the contractor simply was not aware of. This month, I will explain 2 of those 10 critical considerations: Metals and Finishes.

If you’re more interested in curb appeal and beauty than the technical issues, I can assure you that what happens with metals and finishes have an impact on both.

2 Critical Things Most Contractors Don’t Know About Metal Roofing

 

1. Metals

There are different grades and types of metals used in metal roofing and they will have different performance expectations. Which metal is chosen can dramatically impact how the roof performs in terms of durability, energy efficiency, and other things.

With steel, it is important to know not only the type of steel but also the grade of steel in order to estimate its performance. Steel, even with zinc, aluminum, or alloyed metallic coating on it, is still steel. Ultimately, cut edge protection for steel is derived from the zinc in the metallic coating on the steel. There are different grades of steel and better cut edge protection is achieved with better steels. Minimum grades of steel the industry recommends for metal roofing are G90 and AZ50.

Metal thickness is also something to consider but a lot of games are played with steel thickness (referred to as “gauge”). Gauges have significant tolerances and different manufacturers take different approaches to those tolerances, including whether the metal thickness is measured with or without paint. However, the ultimate performance of a roof system typically has far more to do with its design, the coating on the metal, and proper installation than the thickness of the metal.

Steel is inherently stronger than aluminum and copper but that is why the thicknesses of aluminum and copper are greater than those of steel used to produce metal roofing. Some aluminum and copper roofing products may also have optional strengthening backers that can be used to fill up any air space between the metal and the roof deck. All metal roofs require some extra care when walking on them but one benefit is that, unlike roofs made of other materials, they do not lose impact resistance with age.

Aluminum and copper, being non-ferrous metals, will perform better than steel in corrosive environments including coastal regions and areas prone to acid rain. They will not red rust. Copper and aluminum are also more malleable than steel and therefore often available in more intricate product designs. Additionally, aluminum and copper typically have much higher percentages of recycled content than steel does.

2. Finishes

The first defense that a metal roof has against the elements is its outer most coating. Such coatings are typically applied to the metal and baked on while the metal is still in coil form. While metals like copper and zinc are usually used in their “mill finish” states, with steel and aluminum products, the following coatings are common:

Clear Acrylic Coating

This is available typically only on steel with a metallic coating that is predominately aluminum. With this coating, the metal has a “mill finish” look. This is an “entry level” metal roof and it’s important to know that the clear acrylic weathers away over a period of 5 – 7 years. The acrylic is there to facilitate forming of the metal and to protect the metal from scratches during transportation and installation. It wears away quickly.

Polyester Coatings

There are multiple grades of these finishes available. These coatings are named for the resin in the paint and one variation between the different grades is the quality of the pigments used in the paint. Quality pigments will have greater color retention over time but they are still protected to some degree by the resin. The highest performing “super” versions of these coatings show good performance for 7 – 10 years of exposure followed by a fairly rapid and significant decline in fade and chalk resistance.

PVDF Coatings

These finishes are widely respected as the best coatings available for exterior building products today. The resin is based upon the mineral fluorite and the licensors of the resin require only inorganic ceramic pigments for enhanced color performance. These are the most expensive coatings and you will find reduced warranties in bright “exotic” colors as well as metallic colors. A few companies, such as Classic Metal Roofing Systems, also offer powder versions of the PVDF finishes. And like my Dad, our founder Don Miller used to say, “It all starts with the finish.”

Aggregate Coatings

Also known as “stone coatings,” these are typically on steel shake, shingle, and tile products. They are less expensive than quality paint finishes and they are noted for having a very attractive look, with texture and blended colors. In essence, they are similar to the stones on asphalt shingles but they are applied to a steel base. Their typical wear does include granule loss over time and the textured surfaces can be very inviting to streaks and stains from roof algae. Additionally, stone coated products cannot be recycled.

Rest assured that, when you purchase a Classic Roof, all of the above critical things related to metals and finishes have already been taken into consideration to deliver you the best possible roof that meets your requirements for durability, beauty, energy performance and minimizing the ongoing operational costs of your home.

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