Algae growth causes 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.
•Improper installation on a new roof
•Drying and cracking on an old roof
•Dented by improper nailing
•Settling of the structure
•Improperly applied felt
•Roof deck movement
•Spacers not used in between roof deck boards
•Poor roof ventilation
•New shingles applied over old, rough shingles
•Lack of back coating
•Under-saturation of asphalt felt in organic shingles
•Lack of ventilation
•Improper number of fasteners
•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.