A major, often overlooked problem begins with the vent pipe collars on your home. These are the flashing that help seal the PVC pipes that are exiting your roof.  There is a reliable rubber seal on the boots that wrap around the pipe to help prevent water from traveling down the pipe and entering the interior of your home. Often times this rubber will deteriorate due to constant exposure to the weather. Extremes in heat, cold, wind and rain make it necessary to change these vent pipe collars when damage is apparent.