Why Is My Roof Leaking Around the Chimney?

Homeowner Learning

Author: Barbara Horwitz-Bennett | December 12, 2023

While it's sometimes neglected in routine roofing maintenance, the chimney is just as exposed as the rest of the roof and equally vulnerable to deterioration and water leakage. Diagnosing a roof leaking around the chimney can be difficult to pinpoint and repair. However, with some guidance, homeowners can investigate potential warning signs and trouble spots and determine if they should bring in a roofing contractor.

Brick chimney with metal cap, on a shingle roof
A number of issues can be the cause of a roof leaking around the chimney.

Start Inside the Home

For starters, homeowners should check for leaks indoors, around the ceiling area where the chimney enters the home in the attic and in any rooms with a fireplace. Look for stains, sagging plaster, mildewed beams, and other moisture signs, such as crumbling ceiling tiles.

If you do find evidence of moisture damage, it's time to find what's causing the roof leaking around the chimney. Damaged flashing, cracks in the bricks and mortar or a cracked chimney cap are all possibilities.

Flashing, the metal seams along the valleys of the room and around the chimney is a common culprit. Over time, or during a major storm, the flashing can lose its water tightness and must be replaced. A contractor will fix the problem by removing the old metal and installing new flashing.

The expansion and contraction of bricks and mortar as the weather fluctuates from hot to cold can lead to cracking. Similarly, the mortar and masonry around a chimney cap can crack over time. Both of these issues will likely warrant a call to a professional stonemason or chimney repair contractor. Short of a major chimney replacement, it may be possible to locate the leaking area and repoint the mortar or seal the cracks.

One way you can help to protect against leakage here is by adding a chimney cover. In addition to enhanced protection from water, the cover can shield the chimney from falling plant debris and animal intrusion.

Other Causes of Leakage

What if there are no visible issues with your chimney, but you're still finding stains and wet spots? There may be a problem with the roofing material above or adjacent to the chimney. A broken tile or shingle, clogged or weakened gutters, deteriorated underlayment or gaps between the flue liner and chimney can also cause leaks.

Condensation from a furnace can be another surprising cause of chimney woes. With a newer energy-efficient furnace, more heat is kept inside the home, and the small amount of warm exhaust air quickly cools upon entering the wide chimney flue. The moisture that collects from this exhaust can be extremely acidic and can even corrode the mortar inside the chimney.

The best way to prevent a leaky chimney is to keep your roof in good shape. Clear the gutters and downspouts, check for damaged roofing materials and call your local roofing contractor for periodic inspections. An experienced roofing professional can help make sure your chimney keeps the warmth in and water out.