View All Posts

Impact Resistance Test On Metal Roof Panels: Definition Plus Video
Lauren Risotto

By: Lauren Risotto on January 19th, 2022

Print/Save as PDF

Impact Resistance Test On Metal Roof Panels: Definition Plus Video

Corten Roofing

As you’re searching for metal roofing online, you’ve probably come across articles that say that metal roofs are “impact resistant” or that they have a Class 4 impact rating. These are terms that are often thrown around for marketing purposes without a thorough explanation of what they actually mean or why impact resistance is so important to the longevity of your roof.

At Western States Metal Roofing, we recently conducted an impact resistance test of our own on our metal panels, using the official UL 2218 by Underwriter’s Laboratories as inspiration. In addition to reading this article, you can also watch the test in the video below to see what happens. 


What Is Impact Resistance For Roofing?

Impact resistance refers to a roof’s level of resistance from any kind of damage from falling objects such as hail or debris. They are designed to withstand harsh elements that could cause puncturing, tears, cracks or dents.


Why Is An Impact Resistant Roof Important?

Having an impact resistant roof decreases your chances of having cosmetic or functional damage if your roof is struck by a falling object which can include hail, tree branches or other debris. 

A roof material that does not have a Class 4 impact rating, such as asphalt shingles, can experience tearing, ripping, punctures and severe denting when struck with force during a storm. This can result in leaks and parts of the roof needing to be repaired or replaced.


Hail Size And Damage In The United States

Hail, one of the biggest threats to a roof when it comes to impact, creates a lot of costly damage. With 4,611 major hail storms during 2020 alone, insured losses from hail damage have ranged anywhere from 8-14 million dollars a year during the last two decades. 

The damage from hail varies greatly depending on the size of the hail. As we will mention later on in more detail, a  2” steel ball is used during an impact resistance test to represent hail. 2” hail, which is larger than the size of a golf ball, is not very common but will cause damage to anything it comes into contact with. 


Impact Resistant Roof Ranking System

A roof’s impact resistance is represented by a ranking system of Class 1, 2, 3, or 4. As the number goes up, so does the level of impact resistance. A metal roof has a Class 4 impact rating, which is the highest level of impact resistance a roof material can have.


UL 2218 Standard For Impact Resistance

The impact rating for a roofing material is determined by the UL 2218 impact resistance test which is performed by the Underwriters Laboratories, a global independent testing organization. 

During the test, a 2” diameter steel ball is dropped from approximately two stories onto the roof. In order for metal roofing panels to earn the title of a Class 4 rating, the ball must not tear, crack, split or open the panel’s surface.

The Impact Resistance Test Results

From 24 feet in the air, 2” steel balls that weigh 1.185 each were dropped through a tube onto the metal panels. The test was conducted on a 26 gauge standing seam roofing panel and a 26 gauge ⅞” corrugated roofing panel

Both panels were tested in two ways: over a ½” plywood substrate and then suspended between two 2x4s. A metal roof will always have a substrate underneath it, however, we wanted to test the durability of the actual panel itself without anything supporting it underneath. 


Standing Seam Impact Resistance Results

The steel balls did cause denting on the panels when tested both ways, although there was less denting when the panel had the substrate underneath. While the dents are noticeable when viewed up close, they would hardly be visible if the panels were on the roof. 

Most importantly, there was no puncturing or tearing of the panel. This means the weathertightness of the standing seam panel would not be compromised as no entry points for moisture were created by the impact.

⅞” Corrugated Impact Resistance Results

The impact from the test did create dents on the ⅞” corrugated panel when tested both ways. Since the surface of a ⅞” corrugated panel is wavy and not smooth like standing seam, the level of denting partly depends on where the impact occurs on the panel. In this case, there was impact on the low and high of the panel, and the low experienced less denting than on the high of the panel. 

Just like with standing seam, there was no puncturing or tearing of the panel from the impact. The damage that was created was only cosmetic and would barely be noticeable if the panel was on a roof.


Why Choose Impact Resistant Roofing?

When an impact test is conducted, the steel balls represent heavy hail that happens throughout the country. However, your roof can also come into contact with falling branches or debris that can cause similar or even worse damage. 

If you live in an area that experiences extreme weather conditions including heavy snow, rain and high winds, then impact resistance is something you want to seriously consider when choosing your roofing material. 

A roof with a Class 4 Impact Rating can save you from the hassle of water damage and roof repairs. Besides a smaller chance of cosmetic or functional damage, a roof with a Class 4 rating can also save you money on your insurance policy.


For more information about insurance discounts you can get with a Class 4 Metal Roof, we recommend reading:

Metal Roof Insurance Discounts: How Much Will I Save?

Metal Roofing Learning Cener

Get a Free Quote for Metal Roof or Metal Wall Panels Today! Click Here


About Lauren Risotto

Lauren is the Content Manager at Western States Metal Roofing and provides insight on content creation and product promotions.