Every 5th vertical line of shingles

[mikefay]

Recently inspected a one story home, approximately 15 years old. The shingles look good, except that every 5th line running vertically from the top to the bottom was beginning to curl. Shingles are asphalt and are original to the house.

[Jim Katen]

Originally posted by mikefay

Recently inspected a one story home, approximately 15 years old. The shingles look good, except that every 5th line running vertically from the top to the bottom was beginning to curl. Shingles are asphalt and are original to the house.

As the shingles age, the oils in the asphalt slowly evaporate and the shingles become less flexible and shrink slightly. The seal tabs hold the bottom surface of the shingle relatively immobile while the top surface can move. This results in a cumulative curling effect over time.

I usually see slight curling of the outside corner of each shingle (not each tab). If the shingles were properly installed, you should see this curling marching up the roof diagonally. However, if you were to look straight up the roof, the curling would appear to occur every five courses. (Assuming the installer used the [very common] 5-course diagonal method.)

- Jim Katen, Oregon