UL 2218

UL 2218, Standard for Impact Resistance of Prepared Roof Covering Materials, is the most widely used hail-resistance rating for steep-slope roofing in the United States and Canada. It was created in 1996 through work involving insurers, the Institute for Business & Home Safety (now IBHS) and Underwriters Laboratories. The "Class 4" label seen on shingles, metal panels and other roof products usually refers to this standard.

How the test works

Roofing is installed on a test deck according to the manufacturer's instructions. A solid steel ball is dropped from a set height, twice on the same spot, at several locations chosen as the most vulnerable (for example near edges and over joints). The size of the ball and the drop height increase with each class:

Class	Steel ball diameter	Drop height
1	1.25 in (31.8 mm)	12 ft (3.7 m)
2	1.50 in (38.1 mm)	15 ft (4.6 m)
3	1.75 in (44.5 mm)	17 ft (5.2 m)
4	2.00 in (50.8 mm)	20 ft (6.1 m)

After impact the specimens are examined on the face, the back and the underlying layers. For shingles, samples are bent over a mandrel so that hidden cracks open up. A product fails if there is tearing, fracturing, cracking or rupture through the material. Purely cosmetic marks such as granule loss or shallow dents are not counted as failure.

Use in insurance

Many US insurers and some state insurance regulators offer premium credits for roofs rated Class 4 (and sometimes lower classes). In Texas, for example, the Texas Windstorm Insurance Association requires products to be labelled with the impact class and laboratory mark, and the installing contractor must complete a state form. See impact-resistant roof insurance discounts.

Criticisms and alternatives

Because a steel ball delivers a hard, concentrated blow, it does not behave exactly like real hail, which can shatter or flatten. Brittle materials like tile and slate may be penalized, and soft materials may pass while still showing heavy cosmetic damage. For rigid roofing, many specifiers use FM 4473, which fires ice balls. IBHS also runs its own hail ratings for asphalt shingles using laboratory-made hailstones, which it describes as more demanding than UL 2218.

Cosmetic damage

A Class 4 roof can still dent. Some insurance policies in hail-prone states exclude or limit coverage for cosmetic damage to metal roofs, so homeowners are advised to read policy wording alongside the product rating.