Chimney leaks often look like roof leaks, and while water getting into the house under the shingles is possible, it is not a common cause of leaks. It is more likely to be a problem with the flashing, which should be inspected every year. Small cracks should be caulked and your chimney maintenance professional will look for missing, damaged, or loose flashing.
Another cause of a chimney leak that may look like a roof leak is seepage through mortar joints. Over time, continual exposure to water weakens the mortar and both small cracks and large holes can form in it, especially at the joints. This is a relatively easy problem for a chimney professional to deal with, requiring only patches of fresh mortar to be put in place.
There may also be a problem with the chimney crown, which is the very top part of the chimney. Because it has no protection from the elements, it takes the brunt of bad weather, and it is not unusual for a chimney crown to crack in its first year of use. A cracked crown allows water to enter the chimney, widening the crack with time and ultimately causing the chimney’s deterioration.
The seepage of water through a cracked chimney crown usually becomes evident in a darkening of the chimney at the top if made of brick. If the chimney is made from stone, moss or mold may be seen on the crown and around the chimney. At this point, the chimney crown needs to be either repaired or removed and replaced by a trained professional.
If the cracks in the crown are small, hairline fractures, the crown can probably be repaired with the application of a sealer. This is a waterproofing product that seals water out to prevent existing cracks from getting wider or deeper. It essentially resurfaces the chimney crown, and while it is not as permanent a fix as replacing the crown altogether, it is far less costly and fine for minor damage.