Hail as small as 3/4″ to 2″ can damage the protective granular surface on a composition shingle. Homes with wood shingles can split or be punctured. Any damage that may happen only increases as the size of the hail increases. The older the roof, the more damage occurs since the granules are less securely attached to the surface of the shingles. A hail damaged roof will have a reduced “roof life”, resulting in earlier weathering or cracking. As time goes on, it will become increasingly more difficult to make the distinction of hail versus wear. It will be easier to resolve the issues surrounding your hail damaged roof if you take care of it now, rather than waiting down the road to do so. The impact of hailstones on a roof depends on at least these factors:
- Size: The size of the hailstone
- Mass: Some assumptions about the typical mass of a hailstone (ice or ice with some water coating)
- Wind: The effect of wind on the object’s velocity
- Falling height or distance (we assume the distance is sufficient to reach terminal velocity before considering wind effects)
- Mechanics: The assumption that all of the physical energy is converted to kinetic energy as the object strikes the roof
- The pre-existing condition of the roof surfaces, age, existing damage or wear fragility
- The roof slope and angle of presentation of the roof slope to the direction of wind-driven hailstones
A 1 cm hailstone has a theoretical terminal velocity of about 20 mph (9 meters/second). Larger hailstones have a much higher terminal velocity. And a ten-gram hailstone falling from 10 km (this distance is probably more than enough) has a terminal velocity of about 15 meters per second.
Hail damage can dislodge the protective mineral granules of an asphalt shingle, producing areas of exposed asphalt shingle substrate. If inspecting an asphalt shingle (or mineral-granule-covered roof roofing) roof shortly after a hailstorm the exposed shingle substrate should be expected to show freshly-exposed asphalt coated or asphalt impregnated shingle base material.
If the same area is examined much later the exposed shingle areas of granule loss may have weathered or even cracked and this distinction (hail versus wear or other sources of granule loss) will be more difficult to distinguish.
Asphalt shingle blisters are raised bumps or protrusions in shingle surface, either closed blisters or open ones showing a small black pit or crater when the protective mineral granules have been lost from the peak of the blister.