Class 4 is the highest impact rating under UL 2218, the standard most insurers use when they offer hail discounts, and many metal roofing products carry it. A Class 4 hail rating means the panel did not crack or split when struck in the test. It does not mean the roof cannot dent. Here is what the test measures, what it leaves out, and how to pick a metal roof for hail country.
What UL 2218 actually tests
UL 2218 is a drop test. A sample of the roofing, mounted on a deck the way it would be installed, is struck by a steel ball dropped from a set height. Each sample is hit twice in the same spot, and several spots are tested, including edges, seams and overlaps where a panel is weakest. Afterward the sample is inspected from the underside. If the inspector finds any crack, split, tear or opening in the material, it fails that class.
The four classes
| Class | Steel ball diameter | Drop height | What it stands in for |
|---|---|---|---|
| Class 1 | 1.25 inches | 12 feet | Small hail |
| Class 2 | 1.5 inches | 15 feet | Moderate hail |
| Class 3 | 1.75 inches | 17 feet | Large hail |
| Class 4 | 2 inches | 20 feet | Very large hail; the highest class |
The ball sizes and heights are chosen so that the impact energy is in the range of a hailstone of roughly the same size falling at full speed. A product that passes Class 4 has also passed the lower classes.
What the test leaves out
- Dents. The pass criterion is about cracks and openings, so cosmetic damage is not scored at all.
- Ice versus steel. Real hail is ice and often breaks apart on impact. A separate standard, FM 4473, fires ice balls instead of dropping steel ones, and some insurers accept either.
- Wind-driven hail. Storm hail arrives at an angle and at speed, which the vertical drop does not copy.
- Giant hail. Stones larger than two inches fall in some storms, and no residential rating covers them.
- Age. The sample is new. Paint and sealants weather over decades, and the test does not account for that.
Why metal roofs still dent
Steel and aluminum are ductile, which is exactly why they pass the test: instead of cracking like a brittle material, the metal gives a little and springs back or takes a small dimple. The roof keeps shedding water. The downside is that a smooth, wide, flat pan on a thin gauge shows every dimple when the light hits it at a low angle. Aluminum is softer than steel and dents more easily at a similar thickness, which matters if you are choosing aluminum for a coastal house in a hail region.
Whether dents matter is partly up to you and partly up to your insurer. Many insurers that offer a Class 4 discount on metal roofs attach a cosmetic damage exclusion, which means dents that do not cause leaks are not covered. Our insurance and resale guide explains that trade-off.
Choosing a metal roof for hail country
Gauge
Gauge is the thickness of the steel, and lower numbers are thicker. Residential standing seam is usually 24 or 26 gauge, while exposed-fastener agricultural panels are often 29 gauge. For hail, 24 gauge is the sensible choice: it resists denting better than 26 and far better than 29, and it also holds its shape better against oil canning. Thicker metal costs more, but on a roof you plan to keep for 50 years the difference is small. See our guide to metal roof gauge.
Profile
Shape stiffens metal. Ribs, striations and pencil ribs across a standing seam pan make it harder to dent and break up the reflection so small dents disappear. Narrower pans are stiffer than wide ones. Shingle, shake, slate and tile profiles have formed edges and texture that hide hail well, and stone-coated steel adds a granular surface that hides dents better than any smooth finish. Exposed-fastener panels with tall ribs do well between the ribs but can dent on the flats.
Finish and color
Paint rarely cracks from hail on a quality PVDF or SMP finish, so the finish question is mostly about appearance. Low-gloss and textured finishes and medium or lighter colors show dents less than dark, glossy ones. If a cosmetic exclusion is part of your insurance deal, pick a finish and profile that will not show the dents you are agreeing to live with.
Deck and underlayment
A solid deck directly under the panel backs it up on impact. Panels on battens or over open purlins have air behind them and dent more readily between supports. Most Class 4 listings specify the deck and underlayment the product was tested over, so the roof on your house has to be built the same way for the rating to apply. Ask for the listing and have the installer match it.
After a hailstorm
Stay off the roof. Walk the yard and look for dented gutters, downspouts, vents and window screens, which tell you the size of the hail, and take photos from the ground. Then call a metal roofer for an inspection by ladder or drone. Functional damage to look for includes cracked or chipped paint, split or opened seams, torn sealant at penetrations, bent or lifted trim, and broken pipe boots. Dents alone are usually cosmetic. If there is functional damage, call your insurer, and do not sign anything with a door-knocking contractor until you have read it and checked their license and insurance.
Finding a hail-country installer
Roofers who work in the hail belt know which products hold up and which insurers ask for what. Our directory lists metal roofing companies by state, and you can filter by style to find installers who handle standing seam, metal shingles or stone-coated steel.
Frequently asked questions
What does a Class 4 hail rating mean?
Class 4 is the highest impact rating under UL 2218, the test most insurers recognize. A roofing sample is struck twice in the same spot by a two-inch steel ball dropped from 20 feet, and it passes if the material shows no crack, split, tear or opening when inspected afterward. It is a rating for a specific product and assembly, so the panel, gauge and backing on your roof must match the listing.
Can hail dent a Class 4 metal roof?
Yes. The UL 2218 test checks whether the roofing cracks or opens up, not whether it dents, so a Class 4 panel can pass and still show dimples after a big storm. Dents are usually cosmetic and the roof keeps shedding water. Thicker 24 gauge steel, ribbed or textured profiles and stone-coated or shingle-style products hide hail far better than thin, wide, flat pans.
Which metal roof is best for hail?
For hail country, look at 24 gauge steel rather than 26 or 29 gauge, pick profiles with ribs, striations or texture over wide flat pans, and consider stone-coated steel or metal shingles if hiding dents matters to you. Aluminum is softer than steel and dents more easily at similar thickness. Whatever you choose, confirm the exact product and gauge is listed Class 4 under UL 2218.
Does a Class 4 metal roof lower my insurance?
It can. Many insurers in hail-prone states offer a premium credit for a Class 4 roof, but the amount varies by company and state and some insurers attach a cosmetic damage exclusion to metal roofs that take the discount. Call your insurer with the exact product name and gauge before you sign, ask what documents they need, and never rely on a percentage quoted by a salesperson.
Should I file a claim for dents on my metal roof after a hailstorm?
First find out whether the damage is functional or cosmetic. Have a metal roofer inspect the roof from a ladder or by drone and look for cracked paint, split seams, damaged sealant, bent trim and broken pipe boots along with the dents. If your policy has a cosmetic damage exclusion, dents alone may not be covered. Document everything with photos from the ground and talk to your insurer before signing anything with a storm-chasing contractor.