Granule Loss

Granule loss is the detachment of the ceramic-coated mineral granules embedded in the top surface of asphalt shingles and mineral-surfaced roll roofing. The granules give colour, shield the asphalt from ultraviolet light and add fire and impact resistance. Once they are gone, the exposed asphalt dries, cracks and erodes faster.

Some granule shedding is expected. New shingles carry loose surplus granules that come off in packaging, handling and installation, so a light layer in the gutters of a recently installed roof is common. Over the life of the roof, weathering slowly weakens the bond between granules and asphalt, and rain carries granules away.

Causes

• Normal ageing and weathering, usually fairly uniform across a slope; sun-facing slopes tend to wear first.
• Hail, which can knock granules off in random spots and, on older roofs, loosen them even with small stones.
• Blistering, where the blister caps erode and leave pits.
• Foot traffic and scuffing, often along a line where people walk, or at high points.
• Manufacturing variation or flaking from defects in the asphalt or mat.
• Mechanical cleaning such as pressure washing.
• Concentrated water flow from downspouts that discharge onto a lower roof.

How it is assessed

Inspectors look at the pattern. Uniform, gradual loss across a slope generally indicates age. Random, circular spots of missing granules, sometimes with a soft bruise underneath, suggest hail. Linear wear points to traffic. Deep granule sediment in gutters on a fairly new roof can indicate a product or installation issue worth reporting to the manufacturer. Insurers generally treat long-term, uniform granule loss as wear rather than storm damage.

What to do

Granule loss itself is not repaired; shingles that have lost much of their surface are replaced. Owners can reduce avoidable loss by limiting foot traffic, avoiding high-pressure washing, and fitting downspout extensions or splash diverters where upper roofs drain onto lower ones.