Mastering Roof Inspections: Asphalt Composition Shingles, Part 46

by Kenton Shepard and Nick Gromicko, CMI®



The purpose of the series “Mastering Roof Inspections” is to teach home inspectors, as well as insurance and roofing professionals, how to recognize proper and improper conditions while inspecting steep-slope, residential roofs. This series covers roof framing, roofing materials, the attic, and the conditions that affect the roofing materials and components, including wind and hail.  



Functional Damage

A few missing granules do not constitute functional damage. Just the fact that you can see evidence of a hailstrike does not mean that shingles have been functionally compromised. Granule loss has to be visible to the casual observer to qualify as functional damage. If you have to bend down and squint and wonder whether or not you’re looking at a hailstrike, granule loss is not severe enough to qualify as functional damage.

Hail damage to the granule layer is affected by a number of variables, including:

  • the properties of the shingles;
  • the properties of the hailstones;
  • whether the hail is wind-driven; and
  • the orientation of the roof slope to the direction of hail fall.

The ways that these variables combine affect the nature of the granule loss.

Asphalt Quality

The properties of the asphalt layer have a great effect on granule loss because the asphalt is what bonds the granules to the shingle's surface.

As asphalt ages and loses its volatiles and the bond between granules and asphalt deteriorates, it will take less impact-energy for hail to displace granules.

Shingles with old or poor-quality asphalt do not hold granules as well as shingles with newer, high-quality asphalt. This means that old shingles are more likely to lose granules when struck by hail. Even small hail can dislodge granules from older shingles. This is especially true when hail is accompanied by heavy rainwater runoff. Heavy runoff can erode loosened granules.


Shingles less than six months old can experience a lot of granule loss, although this early granule loss does not expose the asphalt.
When shingles are manufactured, in addition to granules embedded into the asphalt, some granules interlock with embedded granules but are not embedded themselves. A lot of these granules come loose during packaging, shipping and installation, but a lot are still attached after installation is completed. These are called “riders” or “hitchhikers.”


During the early part of a shingle’s life, many of these excess granules will be loosened and washed off the roof by storms. Even fairly small hail can increase the rate at which new shingles shed these loosely attached hitchhikers.

Hailstone Properties

The amount of granule loss caused by a hailstrike is affected by the amount of impact-energy carried by the hailstone. The amount of damage done to the granule layer is related to the hail's properties, such as size, density, and free-fall velocity.

Wind-Driven Hail

Wind-driven hail carries more impact-energy, so it may cause more granule loss on older roofs.

The condition of a shingle roof affects the amount of damage that hail will inflict.  As shingles age and deteriorate, they become increasingly brittle and less able to absorb the impact of a hailstrike. Older shingles are damaged more easily than newer shingles.

Shingle quality is also a consideration. Given hail with identical impact-energy, thin, low-quality shingles will suffer damage before thick, high-quality shingles.

On older shingle roofs, many granules may be loose but still in place. These loose granules can be dislodged even by small hail. This is not considered hail damage because the granules were already loosened.


Learn how to master a roof inspection from beginning to end by reading the entire InterNACHI series: Mastering Roof Inspections.

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