What are the causes of roof damage?
There are many causes of roof damage. The most common are:

Neglect

Inadequate maintenance is the most common cause of roof damage. Regularly inspect the exterior of your roof for loose or missing nails, missing or broken shingles or tiles, holes, rotted areas, cracks in caulking and loose or missing flashing. It is also important to check the ceilings and attic for obvious leaks, cracks, gaps and signs of water damage.

Weather

Here in Texas, extreme heat and hail storms are responsible for most roof deterioration. Summer monsoons also cause damage with heavy rains, hail, high winds, blowing debris and lightning. Forceful winds can raise the edge of the roof and loosen nails, roofing materials and flashing, allowing rain to enter the deck and cause rotting.

Flashing Defects

Flashing is the material used to provide a waterproof seal between roof joints and around chimneys, skylights and vents. Roof flashings are usually galvanized sheet metal, but may also be made of aluminum, copper, plastic, rubber or roofing felt. Many roof leaks are the result of flashings that have developed holes or pulled away from the seams.

Vegetation

Trees growing close to the house can damage the roof. Scraping branches scratch and puncture the roofing material, and fallen leaves block gutters and cause water to back up. The combination of heavy foliage and poor drainage can create damp, shady areas in which moss, algae and mold can grow. Moss, algae and mold generally appear as black or green streaks and may rot away wood and roofing material over time.

Poor Design

A sagging roof may be the sign of a structural problem. Any signs of sagging or unevenness in the roof requires immediate repair.