When a fracture occurs due to hailstone impact on a shingle, where does it start?

When a fracture occurs due to hailstone impact on a shingle, it typically starts at the bottom surface. This is primarily because the force of the impact generates localized stress in the material. Hailstones striking the shingle exert pressure, which penetrates through the shingle and initiates a crack from the side that faces the source of the impact. The bottom surface, being the first point of contact with the hailstone, experiences the most immediate and concentrated forces, leading to the formation of fractures.

Understanding the dynamics of this process can help in assessing roof damage and determining the extent of repairs needed. The other surfaces, such as the top, middle, or edges, do not receive the same level of immediate impact stress, which is why fractures are less likely to initiate from those areas.