Hail on roof shingles
Roofing 101

What is Class 4 Impact Resistance and Why is It Important?


Disclaimer: This article is not to be construed as any type of express or implied warranty or guarantee of the impact performance against hail of IKO shingles by the manufacturer, supplier or installer. Damage from hail is not covered under the limited warranty. For further details concerning the FM 4473 standards, visit the FM Approvals website.

In many parts of North America, the frequency of hailstorms is increasing. Hail, especially large hail, can cause significant property damage, including to our roofs. That is why choosing impact-resistant shingles, also called IR shingles, is more important than ever. Asphalt shingles are rated on their impact-resistance, and Class 4 impact resistance is the highest level that they can achieve. Choosing asphalt shingles with a Class 4 rating may be important to help protect your home from hail. It may also be beneficial from your insurance company’s perspective as many companies offer discounts to homeowners who choose Class 4 impact resistant shingles. In this article we will discuss what these shingles are made of, how they are tested to earn their rating and the benefits that they can offer to your home.

Increase in Hail and Severe Weather

Losses due to damage from hailstorms have increased significantly in the United States over the last decade. Annually, hail is estimated to cost $8-13 billion USD in damages. According to Phys.org, research conducted at the University of Albany demonstrates that golf ball-sized or larger hail conditions have increased in many areas across the United States. This includes the area east of the Rocky Mountains, the Centrals Plains, the Midwest and the Northeast. However, serious hail can occur outside of these areas as well.

You do not have to live in an area with high hail risk in order to suffer damages from hail. For example, Phoenix, while not likely to receive hail, had a large hailstorm in 2010. This storm caused the most damage of any hailstorm in U.S. history, according to the Washington Post. Overall, the storm caused $3.2 billion worth of damages in inflation-adjusted dollars. Perhaps most frustrating for homeowners was that there were so many damaged roofs that local roofers were very busy. Some people could not get their roof repaired for a year.

As your home’s risk of seeing a hailstorm, especially a large one, increases, it is wise to learn about ways to identify hail damage when it happens and protect your home.

What Does Hail Damage Look Like on Roof Shingles?

Hail impact may create dips and cracks in shingles. They may be smaller than your thumb which is still enough to open a pathway for water penetration. In exceptionally severe hailstorms, almost as large as your palm. Also, the larger the hail, the more likely it is to crack or rupture the shingle completely open.

hail damage to roof shingle after hailstorm

When large enough hail impacts the roof, it can break the shingles, causing them to crack and lose some granules off the top layer. This damage makes them more vulnerable to water intrusion and other kinds of damage, including UV rays, wind, and future hail damage. Shingles that have been cracked open by hail need to be replaced, or the roof will be at increased risk of water intrusion. A roof that has suffered substantial damage from hail may need to be replaced entirely. If your roof has suffered hail damage, then you will likely want to call a roofing professional to assess what kind of work your roof requires.

The National Weather Service defines hail severity by size as follows:

Hail Classification Hail Size Objects Similar in Size Potential Damage
Small Hail Less than 0.75 inches (19 mm) in diameter Peas to marbles Unlikely to cause damage
Large Hail 0.75 inches (19 mm) to 1.75 inches (44.45 mm) Nickels to golf balls Minor Damage
Very Large Hail 1.75 inches (44.45 mm) to 2.75 inches (69.85 mm) Golf balls to baseballs Moderate Damage
Giant Hail Larger than 2.75 inches (69.85 mm) Grapefruit, softballs and larger Major damage

As you can see large enough hail can make the kind of crater impacts and cracks that we discussed above. Large hail that is on the bigger end of the spectrum can break glass, harm plants, dent vehicles, and cause other property damage. Very large hail can do even more significant damage.

Class 4 impact resistance shingles are tested with a process that replicates the impact of 2-inch hail, as detailed below. However, giant hail is exceptionally dangerous and, so far, there are no tests or standards that indicate a shingle’s potential performance in giant hail conditions. This kind of hail can be responsible for major property damage.

What are Impact Resistant Shingles?

Impact-resistant shingles are designed to be more resistant to damage caused by hail. While each shingle manufacturer creates a product that is a little different, these shingles are typically made with polymer-modified asphalt. This is asphalt with a polymer added into it for increased performance. Many impact-resistant shingles are made with asphalt modified with styrene-butadiene-styrene or SBS. This is a synthetic rubber-based polymer than makes asphalt more flexible to better handle direct impact, even in the cold.

After a significant hailstorm near Dallas, TX in 1992, researching firms working for the insurance industry found that roofing products made with polymer-modified asphalt had performed better in the storm, resisting more damage. Manufacturers then began to incorporate SBS modified asphalt and asphalt modified with other polymers into their products to offer homeowners better hail protection.

Also, manufacturers also typically add a thicker polymer-based mesh to the shingle. Both sides of this mesh are covered with the polymer modified asphalt. The backing helps hold the shingle together when it suffers impact, preventing cracking and splitting. Overall, polymer-modified asphalt is a more robust and more flexible material.

The Classes of Impact Resistance

There are different levels of impact resistance: from Class 1 to Class 4. Class 4 is the highest level of impact resistance and indicates that under lab testing conditions, new shingles can withstand the impact from a 2-inch ball dropped from 20 feet without splitting or tearing.

IKO Nordic Class 4 shingles being lifted to home's rooftop

Impact Resistance Testing

There are two organizations that test new materials and products for impact resistance: Factory Mutual (FM) and Underwriters Laboratories (UL). Both organizations are unaffiliated with manufacturers so that they can offer honest testing. Each organization also has its own test procedure, which we will explain below. While each test’s impact energy is meant to replicate that of actual hailstones, the shingle’s performance in the test can’t be compared directly to its performance in a hailstorm. Largely, that’s because there are other factors in a hailstorm, like the temperature of the shingles, the age of the shingles, roof slope, and much more. The tests simply provide a basis to compare each shingle’s ability to deal with impact forces as manufactured.

Testing for UL 2218

In the Underwriters’ Laboratories 2218 test, researchers drop steel balls onto the shingle surface to replicate the force of hail. This test is intended to assess the mettle of the most vulnerable parts of the roof, such as edges, corners, and unsupported sections and joints.

The test has four ratings. In order to achieve the rating, the shingles have to withstand a steel ball’s impact without cracking. The classification depends on the size of the steel balls dropped from 20 feet above the surface of the shingles:

  • Class 1 shingles can withstand steel balls that are 31.8 mm or 1.25 inches in diameter.
  • Class 2 shingles can withstand steel balls that are 38.1 mm or 1.5 inches in diameter.
  • Class 3 shingles can withstand steel balls that are 44 mm or 1.75 inches in diameter.
  • Class 4 shingles can withstand steel balls that are 50.8 mm or 2 inches in diameter.

The shingles can withstand these hailstones when they are new. As shingles age they may become less resistant to impact forces.

Testing for FM 4473

FM’s test uses ice balls instead of steel balls to drop onto the shingles. Ice balls are denser and harder than most hailstones but also more uniform in shape. They are smooth, while hail is not perfectly round. While the comparison between ice balls and hailstones isn’t perfect, ice balls represent the worst-case hailstones of their size, and they are therefore a reasonable option for this test.

ice balls used to test the impact resistance of asphalt shingles

In the FM test, classification is given for shingles that can withstand ice balls of different sizes without visibly cracking or breaking. The classification is as follows:

  • Class 1 shingles can withstand ice balls that are 31.8 mm or 1.25 inches in diameter.
  • Class 2 shingles can withstand ice balls that are 38.1 mm or 1.5 inches in diameter.
  • Class 3 shingles can withstand ice balls that are 44 mm or 1.75 inches in diameter.
  • Class 4 shingles can withstand ice balls that are 50.8 mm or 2 inches in diameter.

The Class 4 FM test uses the same size ice balls as the steel balls in the Class 4 UL test. It also tests new shingles. It does not account for shingle strength as they age and other important factors such as roof slope and temperature.

Benefits of Impact Resistant Shingles

Are impact-resistant shingles worth it? For many homeowners, the answer is yes. Class 4 impact resistant shingles offer many benefits, including:

  • Meet building codes: Some local building codes at the city or country level may require you to install Class 4 impact resistant shingles when you get a new roof. Typically, these are in areas where hail is a common occurrence.
  • Get insurance discounts: Some insurance companies offer discounts on roofing materials that achieve a Class 4 impact resistance rating. For example, State Farm’s impact resistant shingle discount is available to select customers. These savings may be substantial, even 35% of your home insurance premiums, according to NBC News.
  • Enjoy more benefits: Impact-resistant shingles may also meet other high standards for quality. At IKO, we call these performance shingles. For example, NordicTM shingles are designed to withstand high winds up to 130 mph/110 kmh.
  • Achieve better durability: The most significant benefit of impact resistant shingles is that they will better withstand hailstorms. You can get peace of mind that in a hailstorm, your roof will be as safe as it can be.

IKO Nordic shingles on a home

How to Identify Impact Resistant Shingles

How do you know if the roof shingles you’re interested in are impact-resistant and, more importantly, which class they have achieved? The manufacturer should have this information readily available online. IKO’s impact resistant shingles have their classification listed on their product page and in their brochure.

Are Impact Resistant Shingles Right for You?

Those homeowners who live in an area that gets occasional hailstorms should consider whether Class 4 impact resistant shingles could benefit them. Even if you haven’t experienced a hailstorm in some time, they can happen in most climates in North America. If you are considering impact-resistant shingles, you can find a local roofing company to help using IKO’s Contractor Locator.