A leaky chimney can be difficult to diagnose. It can be frustrating to pinpoint exactly where the water is entering your home because there are so many possible points of entry. Water can enter the home through the flashing which seals the connection between the roof and the chimney, through cracks in the chimney, through cracks in the crown, or via the roof itself. With all of these factors, I recommend starting with the least expensive repair first because the first repair may not always resolve the issue.What may appear as a fireplace leak may actually be entering the home through a number of different places.
One good way to try and pinpoint a general area through which the water is entering is to do a water test. It is very simple to conduct a water test on your chimney on your own. Taking your garden hose start soaking the chimney from the bottom of the chimney to the top, stopping every few feet to let the water soak in for about fifteen minutes. Journal about times and whether you are soaking the left or right side of the chimney. By using this method you will be able to see about how high above the ground the water is entering your home. If there is not further water damage that occurs by this test you may be able to rule out the chimney as the point of entry for the water.
Cracks in the crown must be sealed to prevent further damage from occurring through freeze-thaw damage. Similarly, cracks in the
brick of the chimney itself must be sealed also. Apply a sealant to the cracks in the crown and then apply water repellent over the repair to attempt to arrest chimney crown leaks. I recommend ChimneySaver Water Repellent which is great for use over their crack repair products.
If sealing cracks and waterproofing the chimney and crown does not resolve the issue you’ll want to evaluate your flashing. If the flashing is rusted or has pulled away from the roof or the side of the chimney you will need to replace it. This is the most durable repair and it is fairly inexpensive. If you see no visible points of entry for water you may still try to arrest the problem by sealing the flashing using FlashSeal. This product is painted on and you can use the reinforcement fabric for extra protection. Although the most durable repair is to replace the flashing completely sealing your flashing is less expensive and more easy to do by yourself.
If you are really having trouble diagnosing your water problem you may want to have a professional come out to evaluate the job for you. Diagnosing chimney leaks is always a process of elimination and I always recommend going with the least expensive repair first to see if that will arrest the issue. If a chimney company comes out and suggests rebuilding the chimney without bothering to try any less expensive repairs I would be wary.