Roof leaks around a chimney are more common than you may think. Fortunately, you can usually repair the roof at the site of the damage without the need for a full roof replacement. 

1. Improper Flashing Style

When done properly, the roof flashing on the side of the chimney should resemble steps. If the top of the flashing is flat or a non-stepped slope, then it isn't installed properly and it is much more likely to allow water to leak behind the flashing and through the roof. Chimney flashing also has a lip along the bottom, designed to cover the gap between the shingles and chimney. If this is missing, then the flashing is only for show as no sealing is possible.

2. Caulking Shortcuts

Caulking is not the proper way to seal a chimney, however, it's not uncommon to see DIY use caulk to seal up gaps around the chimney. Sometimes the caulk is applied around the edges of the flashing, while in others caulk may be the only type of seal being used around the chimney. This poses a major problem because caulk will crumble and crack fairly quickly, which means that it doesn't provide a suitable waterproof seal.

3. Past Leak Damages

Sometimes a chimney is flashed properly now, but it wasn't always in the past. If a past leak has led to rotten sheathing around the chimney or damaged shingles just under the flashing lip, it's more likely that future leaks will continue to be a problem as the sheathing and shingles continue to degrade. An inspection of the roof can determine if there is hidden damage from a past leak, and then your roofer can repair it.

4.  Failing Flashing

Flashing, even installed correctly, won't last forever. In many cases, the flashing may not even last as long as the rest of the roof. Hail and wind damage, along with rust and corrosion, can lead to a much shorter functional life. It only takes a few small pinprick holes or warping for a leak to occur. An annual roof inspection can catch deteriorating flashing before it fails completely.

5. Damaged Masonry

The masonry of the chimney is another common area for a roof leak to begin. This issue often comes as the mortar ages and begins to crumble. This leaves gaps between the bricks which act as channels to route moisture behind the flashing against the side of the chimney. If this is damaged, the mortar must be repaired and the flashing may need to be replaced. 

Contact a roofing contractor if you suspect a leak near the chimney.