Roof damge can happen in an assortment of ways and in various places on a roof. If you have a home that has a south facing roof, look here first. The ultra-violet rays from the sun are the number 1 factor when it comes to damage on a roof. You also want to look at the flashings around any of the penetrations. The rubber gasket around the pipes and the silicone used on the corners of any metal flashings will not last forever.
You may also want to look at the eave edges to determine if there is any water wicking back on the plywood edge. On homes that are new, eave flashing a lot of times is not installed and this leaves the edge of the plywood exposed. Exposed plywood overtime can delaminate, buckle, and begin to dry rot.
In the valleys of the roof, check the condition the flashings. If you have an asphalt shingle roof, and you have a "cal-cut", or "woven" valley check the condition of the shingles in the trough. The granules off these shingles will wear out faster than the rest of the roof, leaving the asphalt exposed to the sun. The shngle is then more prone to splitting or tearing.
On shake roofs you really have to perform an "on the roof" inspection to truly see the condition of the roof. If shakes are split it can leave the felt underlayment exposed to crack and split, and leaving an open hole to yopur attic space. That being said, not all cracks in the felt will leak. You may go into your attic space and see all kinds of daylight spots through the roof. If you see more than pin hole size streaks, than you shoud have a professional evaluation performed to see if repairs or a new roof is needed.
With all of the possibilities, we recommend calling Pressure Point Rooofing, Inc to inform you of the condition of your roof and what would be recommended for the best results.