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Posted by McElroy Metal ● Jul 19, 2022 9:31 AM

What is a Class Four Roof?

Most products undergo various testing during development to ensure performance and consumer safety. Metal roofing is no different. Routine metal roofing product testing covers everything from structural integrity topics like uplift to the ability to resist fire and flame spread.

We’re frequently asked about various testing standards and how designers and consumers should use the testing results in the real world.

To help our readers understand, let’s dig into the specifics of Class 4 testing. First, it’s important to understand that Class 4 is an impact test standard used for shingles and metal roofing.


How is Material Tested?

Underwriters Laboratories (UL) is a not-for-profit independent testing organization that delivers verified information to help consumers make accurate product decisions.

UL developed a test to rate the strength of roofing materials called the UL 2218 Impact Rating. These test results help determine if a roofing material is Class 1,2,3 or 4.

As the chart below depicts, UL 2218 testing is completed by dropping four different-sized metal balls from various heights (to simulate hail). If the test product tears or fractures, it is considered a failed test. drop-height-kinetic-energy

Are all shingles and metal roofs class 4 roofs?

The short answer to this question is no. In fact, the vast majority of shingle roofs haven’t been impact tested. Interestingly, those with successful Class 4 testing run 10-20% more expensive than their non-testing counterparts.

In contrast, most metal roofs are impact-resistant and rated Class four. McElroy Metal has over two dozen profiles in steel with a Class 4 rating available in thicknesses down to 29 gauge.

Class 4 ratings in alternative metals such as aluminum and copper are also available, although much less frequent. How do I know if I have an impact-resistant roof?

Determining if your roof is (or isn’t) impact-resistant can take a couple of different paths. For metal roofing, UL does not recognize a panel as being UL 2218 classified unless the label shown below is attached.ul-classified-max-rib

You can also visit the manufacturer's website where you purchased the material and look for completed testing information. For example, as shown below, McElroy Metal offers this information in the Downloads section of our website and on individual product pages.


Shingles are rated Class 1 through 4, with Class 4 shingles having the highest impact resistance. Typically, you cannot tell the impact rating by looking at a shingle.

The underside of the shingle or packaging usually shows the impact rating.

What does it take to get a Class 4 rating?

To achieve a Class 4 rating, a 2” in diameter steel ball dropped from a distance of 20’ above the roof must “show no evidence of tearing, fracturing, cracking, splitting, rupture, crazing or other evidence of opening” during the test procedure.

Why is impact resistance important?

Impact resistance is important because it measures resistance to hail and debris. Generally speaking, you can’t label something as “hail proof,” but products classified as Class 4 meet the most substantial level of resistance that UL has deemed appropriate. 

With Class 4-rated metal systems, your roof is far more likely to remain watertight even after storm damage. Consequently,  purchasing products with a Class 4 rating means you will have a smaller likelihood of damage after a hail event or a storm where debris has made contact with your roof.

Furthermore, replacing a roof is not the only expense when roofing fails – if the hail/debris causes a leak, additional damage is likely to occur inside the building.  

And if reducing the chance for water penetration after a storm isn’t reason enough, there is more.

Based on years of data showing Class 4 roofing products lead to lower lifetime roofing costs and fewer replacements, many insurance companies offer reduced insurance premiums for those using Class 4 products.

Would you like to know more about the test standards used for metal roofing products?  If so, check out our earlier post, “How to Make Sense of Metal Roof Panel Testing” or simply contact us.  We’re always here to help!

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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: Education, Metal Roofing, FAQ, Wind/Hail

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