When Should You Expect To Replace a Roof?

There are basically two styles of roofing shingles used in our area. Three tab shingles and dimensional (often referred to as architectural) shingles, both are asphalt type with a fiberglass matrix and covered with limestone grit. Longer life shingles have more grit than less expensive shorter life shingles.

Three tab shingles are usually twenty year life expectancy and tend to last about fifteen to seventeen years.
Most of the dimensional shingles have a thirty year life expectancy which will last about twenty five years in our area.

The length of time that roofing shingles will remain functional is affected by numerous conditions, some of which are outside most home owners control. The primary aging factor for shingles is weather. Temperatures at both ends of the thermometer naturally reduce the life of the shingles down from the advertised life expectancy. Then extremes of hot summers or cold winters combined with strong winds and storms blowing debris like leaves and twigs over the roof further age the roofing. Hail storms can destroy a perfect roof in a matter of minutes.
Moss and algae often found growing on shaded areas of the roof, develop small roots that over time will grow into the shingles surface causing failure.  
The flatter the roof pitch (slope) the shorter the life expectancy of a shingle, the steeper the roof, the longer the life of the shingle, sometimes exceeding the published life of the shingle.
Badly ventilated or worse still, unvented attic spaces will shorten the life of shingles due to the excessive heat that can develop and reach one hundred and seventy degrees or higher when its one hundred degrees outside.The height and angle of a roof, can make it difficult to see when viewing from the ground the actual condition of the shingles. A worn out roof, one that is at the end of its life but not past that point can often appear to be in reasonable condition when viewed from the ground.

Indicators that a roof is coming to the end of its functional life and should be considered for replacement are easy to observe.

Fiberglass matrix visible on the edge of the shingles, or areas where there is little or no grit.