Causes of an Aging Roof System

Inspecting the roof is a major component of your home inspection.  A roofing system that is worn-out can no longer perform and is prone to leakage.  We see many styles of roofing systems, and roofing materials have varying life expectancies. Under normal conditions, architectural asphalt shingles have a life expectancy of around 25 years. It is not unusual for slate or clay tile roofs to last over 100 years. There is a church in England with a slate roof that is over 1200 years old!

The roof is one of the first components we examine when we begin the home inspection. We determine the number of layers of roofing material.  This is important because if there are two layers of shingles present, when it is time to reroof, all the material will have to be stripped and laid fresh.  If we find more than two layers, it is indicative of a poor roofing job and additionally the structure may be unable to support the added load of extra roofing layers.

The next step is to examine the condition of the roof.  There are many components that can cause a roof to age prematurely. These include:

  • Excessive exposure to ultraviolet light: This is typically an orientation issue (is the roof facing north, south, east, or west?).
  • Color: While this is a controversial issue, many believe that darker-colored asphalt shingles wear out before light colored shingles. This is dependent on climate and hours the shingles are exposed to direct sunlight.
  • Ventilation: Good ventilation helps to keep the roof cool in the summer, and in the case of wood shingles, for example, helps the shingles dry after a rain. Poor ventilation can cause rapid aging.
  • Exposure to winds: A house located in a coastal area or at the top of a hill is exposed to different winds than a house surrounded by tall trees and other homes in a mature neighborhood. Mechanical action of wind can cause immediate damage if roofing materials are torn off, or can affect the life expectancy of the roof through the abrasive action of wind-driven rain, hail, snow, or debris.
  • Slope (Pitch): Generally, steeper roofs last longer than shallow roofs. Water runs off steep roofs more quickly and the roof dries faster.
  • Complexity: The more complex the roof, the shorter the life expectancy. Complex roofs include those with many changes in direction many valleys, penetrations and or roof-mounted equipment. Every time there is a penetration, or change in direction or material, there is an increased potential for failure.
  • Foot traffic: Roofs that are walked on regularly will not last as long as other roofs. Some parts of the roof may see a lot of foot traffic and tend to wear out first. This may be an area where it is easiest to get from one part of the roof to another, or an area below a dormer, where people may stand to clean windows.
  • Concentrated water on the roof from a drainage system above: It is common for an upper roof to have a gutter or downspout that discharges onto a lower roof. Collecting all the water from the upper roof and allowing it to run across one section of the lower roof will wear out this section prematurely.
  • Tree Branches: Branches touching the roof cause abrasion damage and permanent failure. Even if he branches don’t touch the roof, the overhanging trees drop debris on the roof and shade the roof, slowing the drying process.

It is unfortunate that we often find the homeowners representation of the roofs age to be incorrect. We’d like to think that years go by quickly and the error is a miscalculation rather than a misrepresentation. Unless you see an invoice for repair or replacement, take this information with a grain of salt.  We’ve found our clients are more concerned with the amount of remaining life in a roofing system much more than the actual age of the roof.

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