Impact-Resistant Shingle

An impact-resistant shingle is a roofing product, usually an asphalt shingle, that has been tested and classified for resistance to hail. In North America the most common rating is from UL 2218, a standard established in 1996 that ranks products from Class 1 to Class 4. A "Class 4 shingle" is one that has achieved the highest class.

The UL 2218 test

Steel balls of increasing size are dropped onto installed samples, simulating hailstones. For Class 4, a 2 in (51 mm) steel ball is dropped twice on the same spot from about 20 ft (6.1 m). The product passes if there are no ruptures or cracks through the shingle when examined immediately afterwards. Classes 1-3 use smaller balls.

How shingles achieve it

Manufacturers use one or more of these methods:

• Polymer-modified asphalt (often SBS rubber), which makes the shingle more flexible so it absorbs energy instead of cracking.
• Reinforcing scrim or fabric on the back of the shingle.
• Thicker laminated construction.

Other materials can also carry Class 4 ratings, including many synthetic slates and shakes, some metal panels and some concrete tiles.

Insurance and codes

Texas required insurers to offer premium discounts for Class 4 roofs as early as 1998, and several other US states and insurers offer discounts or credits; availability varies widely. Studies from the 1960s found that hail damage to shingles typically starts with stones larger than about 1.5 in (38 mm).

Limitations

The rating describes resistance on a new product under laboratory conditions. Shingles age, and stiffened asphalt is more vulnerable. A Class 4 label does not mean the roof cannot be damaged by very large hail, and cosmetic dents or granule loss may not be covered by a manufacturer's warranty.