Very often, if you discover leaks in your ceiling near the chimney, the problem is a leak that has been exposed in the chimney flashing. Making small adjustments to the chimney flashing is an easy and simple process, but should be attempted during clear weather when the wind is not blowing.
Caulking the Flashing
Very often, the problem with chimney flashing is that the caulk has either somehow been destroyed or is no longer doing the job of sealing the flashing against the chimney and the roof shingles. In order to repair this problem, it is necessary to recaulk the flashing.
Purchase one or two tubes of water proof silicone caulk and install a tube in a caulk gun. Using a secure ladder climb up to the roof. If possible, have someone stand at the bottom of the ladder for safety. If this is not possible, then use a safety harness or a length of rope to secure yourself to the chimney (tie the rope around your waste and the chimney).
Clear away any debris, dirt or other materials from around the chimney. Inspect to see if there are any damaged shingles. If there is no damage, then apply a thick layer of caulk around the edge of shingles where they meet the flashing (the flashing is the metal that runs along the bottom of the chimney where it meets the roof). Apply another layer of caulk along the flashing where it meets the chimney.
When the caulk is dry, check the seal by spraying water on the roof with a water hose.