|Sun: Heat and ultraviolet rays cause roofing materials to deteriorate over time. The deterioration can occur faster on the sides facing west or south.
Rain: When water gets underneath shingles, shakes, or other roofing materials, it can work its way to the deck and cause the roof structure to rot. The extra moisture encourages mildew and rot elsewhere in the house, including damaged walls, ceilings, insulation, and electrical system.
Wind: High winds can lift the edges of shingles (or other roofing materials) and force water—and debris—underneath them. Very high winds can do extensive damage.
Snow and ice: Melting snow often refreezes at the roof’s overhang (where the surface is cooler), forming an ice dam and blocking proper drainage into the gutter. Instead, the water backs up under the shingles and seeps into the interior. During the early melt stages, gutters and downspouts can be the first to fill with ice and be damaged beyond repair or torn off the house.
Condensation : Condensation can result from the buildup of relatively warm, moisture-laden air. Moisture in a poorly ventilated attic promotes decay of the wood sheathing and rafters, possibly destroying the roof structure. The solution may be to increase attic ventilation through the use of larger or additional vents so the attic air temperature will be closer to the outside air temperature.
Moss and algae: Moss can grow on wood shingles and shakes if they are kept moist by poor sunlight conditions or bad drainage. Once it grows, moss holds even more moisture to the roof surface, causing rot, and its roots actually work their way into the wood. Algae also grows in damp, shaded areas on wood or asphalt shingle roof systems. Besides creating an ugly black-green stain, algae can retain moisture, causing rot and deterioration. Trees and bushes should be trimmed away from the house to eliminate damp, shaded areas, and gutters should be kept clean to ensure good drainage.
Trees and leaves: Tree branches touching the roof will scratch and gouge roofing materials as they are blown back and forth by the wind. Falling branches from overhanging trees can damage—or even puncture—shingles and other roofing materials. Leaves on the roof system’s surface retain moisture and cause rot, and leaves in the gutters block drainage.
Missing or torn shingles: The key to a roof system’s effectiveness is complete protection. When shingles are missing or torn off, the roof structure and interior of the home are vulnerable to water damage and rot. The problem is likely to spread—nearby shingles are easily ripped or blown away. Missing or torn shingles should be replaced as soon as possible.
Shingle deterioration: When shingles get old and worn out, they curl, split, and lose their waterproofing effectiveness. Weakened shingles are easily blown off, torn, or lifted by wind gusts. The end result is structural rot and interior damage. A deteriorated roof system only gets worse with time, and it should be replaced as soon as possible.
Flashing deterioration: Many apparent roof leaks really are flashing leaks. Without good, tight flashings around chimneys, vents, skylights, and wall/roof junctions, water can sneak into the house and cause damage to the walls, ceilings, insulation, and electrical system. Flashings should be checked as part of a twice-yearly roof inspection and gutter cleaning.