"Weathering" is a general term used to describe the effects on shingles of long-term exposure to the elements.
Weathered shingles aren’t necessarily damaged shingles, although weathering will eventually damage shingles. Weathering is a natural process that causes shingles to deteriorate over time. The rate at which shingles weather can be affected by a number of things.
Shingle Quality
Low-quality shingles will fail before high-quality shingles. Quality can vary widely among manufacturers, and even within a single manufacturer’s product line.
Structure Orientation
South-facing roof slopes have shorter lifespans due to increased thermal cycling and UV exposure. Some portions of the roof are affected by prevailing winds more than others.
Degree of Roof Slope
Flatter roofs have shorter lifespans because they shed moisture more slowly and are more directly exposed to UV radiation than roofs with steeper pitches.
Climate
Harsh climates shorten roof lifespans. Wind, moisture and thermal cycling all contribute to deterioration of roofing materials.
Thermal Cycling
Climates with large daily temperature swings shorten roof lifespans because they cause greater amounts of expansion and contraction. This increases the roof's rate of deterioration.
Roof Color
Darker roofs absorb more heat, which shortens shingle lifespan by accelerating the loss of volatiles and increasing thermal cycling.
Elevation
Homes at higher elevations are exposed to more UV radiation, which deteriorates most roof-covering materials, including asphalt shingles.
Roof Structure Ventilation
Poor ventilation of the roof structure shortens shingle lifespan by failing to keep shingles cool, resulting in accelerated loss of volatiles and greater amounts of thermal cycling.
Quality of Maintenance
Failure to repair damage and keep roofs clean can result in damage and deterioration from moisture intrusion and wind.
Source: National Association of Certified Inspectors
