Which rating signifies the highest impact resistance for asphalt shingles?

The rating that signifies the highest impact resistance for asphalt shingles is a "4." This rating is part of a standard established by Underwriters Laboratories (UL), known as the UL 2218 standard. The impact resistance of asphalt shingles is tested using steel balls dropped from a specific height, and the shingles are then assigned a rating based on their performance.

A rating of "4" indicates that the shingles can withstand impact from larger stones at higher velocities without sustaining damage. This rating is particularly important in areas that experience severe weather conditions, such as hail storms. Higher-rated shingles provide better protection and durability, ultimately leading to a longer lifespan for the roofing material and reducing the likelihood of costly repairs due to impact damage.

Ratings lower than "4," such as "2" and "3," indicate lesser resistance to impact, meaning they are more susceptible to damage from impacts, and thus do not provide the same level of protection as those rated "4."