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Impact resistant shingles are products that have passed the UL 2218 steel ball test without cracking the mat, and Class 4 — a two inch ball dropped twice on the same spot — is the top rating in the series and the one insurers recognise. Most achieve it with polymer modified SBS asphalt that flexes and rebounds instead of fracturing, sometimes with a reinforcing scrim laminated to the back, which also makes them heavier per square and more forgiving in cold weather and under foot traffic. This guide explains all four impact classes and exactly what the test does not cover, how the construction differs from standard architectural shingles, and the three questions to ask your carrier before choosing a product: whether they credit a Class 4 roof, how much, and what documentation they need. It closes with a table of situations where the upgrade is a strong case and where standard architectural shingle is enough.
Impact-resistant shingles are rated by a standardised steel-ball drop test, UL 2218, on a scale of Class 1 to Class 4. Class 4 is the top rating and it is the one insurers recognise.
| Class | Steel ball drop | Meaning |
|---|---|---|
| Class 1 | 1.25 in ball | Lowest rating |
| Class 2 | 1.5 in ball | |
| Class 3 | 1.75 in ball | |
| Class 4 | 2 in ball | Highest — no cracking on the back of the shingle |
The test drops the ball twice on the same spot from 20 feet and the shingle passes if there is no cracking on the reverse. It is a laboratory test of one failure mode — it is not a guarantee against hail damage.
Insurers want documentation: the product, its UL 2218 Class 4 certification, and the installation invoice. Get all three from the contractor at the time and send them to the insurer rather than assuming the discount applies automatically — it usually does not.
Short answer: A shingle passes UL 2218 Class 4 when two hits from a 2-inch steel ball dropped 20 feet onto the same spot leave no crack or split. The class is printed on the bundle wrapper and the product data sheet — Owens Corning TruDefinition Duration FLEX and Duration STORM, for example, are both sold as UL 2218 Class 4.
There is no single list to look up on the roof — the rating belongs to a specific product line, and one brand family can include both rated and unrated shingles. Check it this way before you sign a quote:
Source: Roofing Contractor, “Owens Corning Roofing Expands Availability of TruDefinition Duration FLEX, Duration STORM Shingles”.
| Class | Steel ball | Drop height | Passes when |
|---|---|---|---|
| Class 1 | 1.25 in | 12 ft | No crack or split after the impacts |
| Class 2 | 1.5 in | 15 ft | No crack or split after the impacts |
| Class 3 | 1.75 in | 17 ft | No crack or split after the impacts |
| Class 4 | 2 in | 20 ft | No crack or split after two hits on the same spot |
Dents and granule scuffs are allowed; cracking through the shingle is not. The hail damage calculator compares a storm’s hail size with these ball sizes.
Source: UL 2218 class summaries published by Black Hill Roofing and CeDUR (the standard itself is sold by UL).
Related: Hail damage roof calculator · Roof insurance claim guide
This site’s 2026 band for standard architectural shingles is $450–$650 per square installed. The Class 4 premium on top of that depends on the product line and your supplier, so price it from your own quotes:
| Premium per square | Upgrade on 25 squares | Payback at $200/yr credit | Payback at $400/yr credit |
|---|---|---|---|
| $50 | $1,250 | 6.3 years | 3.1 years |
| $100 | $2,500 | 12.5 years | 6.3 years |
| $150 | $3,750 | 18.8 years | 9.4 years |
A payback shorter than the 25–30 year life of an architectural shingle roof means the credit alone covers the upgrade.
Related: Asphalt shingle roof cost calculator · Shingles calculator
Only product lines whose data sheet states a UL 2218 class. Owens Corning TruDefinition Duration FLEX and Duration STORM are both sold as UL 2218 Class 4. Check the exact line on the data sheet and the bundle wrapper, because one brand family can include unrated shingles.
Class 1 uses a 1.25-inch steel ball from 12 feet, Class 2 a 1.5-inch ball from 15 feet, Class 3 a 1.75-inch ball from 17 feet and Class 4 a 2-inch ball from 20 feet. The shingle passes if it does not crack or split.
Get the standard and Class 4 lines priced as separate line items and subtract. Standard architectural shingles run $450–$650 per square installed on this site’s 2026 band; a $100-per-square premium adds $2,500 to a 25-square roof.
They are shingles that have passed the UL 2218 steel-ball impact test without cracking the mat. Most achieve it with a polymer-modified (SBS) asphalt that stays flexible instead of shattering, or with a reinforcing mesh on the back. Class 4 is the top rating in the series and the one insurers usually recognise.
Class 4 is the highest UL 2218 impact classification. In the test a two-inch steel ball is dropped twice on the same spot from twenty feet, and the shingle passes only if the mat does not crack or split. It is a laboratory rating, not a guarantee against hail damage — very large or wind-driven hail can still damage a Class 4 roof.
Many carriers offer a discount for a documented Class 4 roof, and in hail-prone states some make it a condition of favourable roof coverage. The size of any discount is set by the carrier and the state, so ask yours directly what they credit and what documentation they need. Keep the manufacturer’s product certification and your installer’s invoice on file.
The case is strongest where hail is frequent: a longer service life, fewer claim cycles, and often a premium credit that offsets some of the upfront difference. Where hail is rare, the extra cost buys mainly durability and wind performance rather than a financial return. Ask your carrier for the credit first — that number is what tips the calculation.
The asphalt is modified with polymers so the shingle flexes and rebounds instead of fracturing, and some products add a reinforcing scrim on the back. They are usually heavier per square, sometimes need a slightly different fastening pattern, and stay pliable at lower temperatures — which is also why they handle wind and foot traffic better.
Not meaningfully. Class 4 products come in the same architectural and designer profiles and the same colour ranges as standard lines, so the roof looks like any other quality shingle roof. The difference is in the mat and the asphalt, not the appearance.
Yes. The rating means the mat survived a specific standardised impact, not that the roof is hail-proof. Large stones, wind-driven hail striking at an angle, and repeated storms all still cause damage — including granule loss and bruising that an adjuster will assess the same way as on any other roof.
Picking a colour in an impact-rated line? See how to choose shingle colour.
Check what the maker actually covers before you pay the premium; the roofing warranty guide explains material and workmanship cover.
Considering a Class 4 metal roof instead? The stone-coated steel roof cost calculator prices it at $7–$13 per sq ft installed.
Class 4 lines often pack 4 bundles to the square. Check how many bundles of shingles in a square for the line you pick.