What are impact resistant shingles made of?
The layers inside
- Mat. Like standard shingles, a fiberglass mat forms the core. Some impact rated lines use a heavier or reinforced mat.
- Modified asphalt. The key ingredient. SBS (styrene butadiene styrene) polymer blended into the asphalt gives it rubbery elasticity. When a hailstone hits, the shingle absorbs and spreads the energy instead of fracturing the mat.
- Backing reinforcement. Many products laminate a polyester or polymer fabric to the underside, which holds the shingle together even if the surface bruises.
- Granules. Ceramic coated mineral granules on top, the same as other shingles, often with algae resistant granules mixed in for humid places like Georgia.
How the rating is earned
UL 2218 sorts shingles into Class 1 through Class 4 by dropping steel balls of increasing size from increasing heights. Class 4, the top, means samples struck twice in the same spot by a 2-inch ball dropped 20 feet showed no crack on the front or back. The rating is printed on the bundle wrapper, so check the label rather than the brochure. A related standard, FM 4473, fires ice balls at the shingle instead.
What that means on a Georgia roof
Rubberized shingles shrug off much of the hail around an inch in diameter that North Georgia sees in spring, but they are not hail proof, and the granule surface can still be scuffed. They also stay flexible longer in heat, which helps them resist cracking as they age. Some insurers give a premium discount for a Class 4 roof, so ask your agent before you choose. For the bigger picture, see impact resistant shingles in Georgia and Georgia hail season.