Code & Standard
What Is Class 4 Impact Resistance (UL 2218)?
Also called: UL 2218 Class 4, Class 4 hail rating, impact-resistant roofing
Class 4 is the highest rating in UL 2218, the standard impact test for roofing. To earn it, a roof covering must withstand a 2-inch steel ball dropped from 20 feet — twice on the same spot — without cracking, splitting, or rupturing. Many insurers discount premiums for Class 4 roofs in hail regions.
In plain English
Imagine hail the size of a billiard ball. UL's test drops a steel ball that size from two storeys onto the roofing — then does it again in the same spot. If the material's water-shedding integrity survives without cracking or splitting, it earns Class 4. Classes 1 through 3 use smaller balls and lower energies.
How class 4 impact resistance works
UL 2218 measures functional survival, not cosmetics: the pass/fail is whether the covering (and its coating, for metals) cracks, tears, or ruptures so water could pass. That distinction matters two ways. For asphalt, hail bruising that knocks granules loose ages the roof even when it technically passes early. For metal, severe hail may leave cosmetic dents while the interlocked, continuous metal surface remains completely watertight — which is why insurance policies in hail country often pair Class 4 premium discounts with "cosmetic damage" exclusions. Heavy-gauge interlocking aluminum systems carry Class 4 as a system rating, panels and locks together.
Why it matters for your roof
Hail is the single largest property-insurance peril in much of North America. A Class 4 roof can earn meaningful premium discounts, avoid the repeat-replacement cycle asphalt suffers in hail alley, and — in metal — fail cosmetically at worst rather than functionally.
Common problems
Confusing cosmetic denting with functional failure; assuming the rating transfers when only the panel (not the installed system) was tested; insurers' cosmetic-exclusion riders surprising owners after storms.
Don't confuse it with
Not to be confused with Class A fire resistance — a separate rating for fire exposure, not impact.
- UL 2218 Class 4 vs Class 3 (smaller ball, lower energy)
- UL 2218 vs FM 4473 (ice-ball test used for some products)
Regional & climate notes
Most relevant in: Hail-prone regions.
Frequently Asked Questions
Does a Class 4 roof lower my insurance?
Often, yes — many insurers in hail regions offer premium discounts for documented Class 4 coverings. Ask your carrier for their impact-resistant roof credit and keep the product documentation.
Can hail still dent a Class 4 metal roof?
Extreme hail can leave cosmetic dents in any metal, but a Class 4 interlocking aluminum roof is engineered to stay completely watertight — the dent is a blemish, not a breach.
Is Class 4 the same for asphalt and metal?
The test is the same; the aging isn't. Hail that bruises asphalt sheds granules and shortens its life even when rated; metal's integrity doesn't depend on a sacrificial surface.
Related terms
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