Rotting is caused by absorption of moisture by the mat at the core of the shingle. This is a common problem with organic-based shingles.
Normally a certain number of granules will be loose, especially after application. These granules are called "riders" and are a normal result of the manufacturing process. Granule loss does not affect the service life of the shingles unless granules can be seen missing on the surface of the shingles, thus exposing the asphalt or Fiberglas® mat.
Spots are caused by leaks in the roof.
Moisture in the shingle
Exposure to high winds.
and health problems associated with the use of Ceiling Spots.
Lack of back coating
Under-saturation of asphalt felt in organic shingles
Lack of ventilation
Improper number of fasteners
Improperly applied felt
Roof deck movement
Spacers not used in between roof deck boards
Poor roof ventilation
New shingles applied over old, rough shingles.
Improper installation on a new roof
Drying and cracking on an old roof
Dented by improper nailing
Settling of the structure.
a dark discoloration on roofs. The algae is usually brown to black in color which results in a streaked, dirty looking rooftop. It can be mistaken for soot, dirt or tree droppings, which typically produce only localized discoloration. It's caused by the growth of air-borne algae which deposits on your roof. The good news is that algae growth does not affect the service life of your roofing material. It occurs most often in warm, humid climates such as the Southeast (where algae-resistant shingles are available).