According to Environment Canada, the severe thunderstorm warning criteria for hail is when hailstones of 20 mm in diameter or greater (nickel-sized or larger) are expected[3].
The degree of damage to properties, however, varies according to the individual hailstone size, shape and density, the duration of the hailstorm, the concentration of hailstones, and the accompanying wind speed and direction. Depending on these factors and the type of property at risk under consideration, the types of damage from hail could be cracks, tearing, spatter marks, dents, or cap sheet membrane damage[4].