The most common causes of a leaking chimney are failed or poorly installed flashing, a cracked chimney crown, a missing or damaged chimney cap, deteriorated mortar joints, porous brick that soaks up water, and condensation inside a flue serving a gas or oil appliance.
1. Flashing
The metal seal where the chimney meets the roof. Caulk-only or rusted flashing is the #1 cause of leaks. Fix: new step and counter flashing cut into the mortar joints.
2. Cracked crown
Water pours straight into the masonry through crown cracks. Fix: crown sealant for small cracks, or a rebuilt crown.
3. Missing cap
Rain falls straight down the flue. Fix: a properly sized stainless or copper cap.
4. Mortar joints
Cracked or missing mortar lets water in between the bricks. Fix: tuckpointing.
5. Porous brick
Brick absorbs water like a sponge, especially in wind-driven rain. Fix: a breathable masonry water repellent.
6. Condensation
Gas and oil appliances produce moist exhaust that can condense in a cold or oversized flue, causing stains that look like leaks. Fix: a correctly sized, insulated liner.
Temporary steps until we arrive
- Put a bucket or towels in the firebox
- Don't use the fireplace until it's inspected
- Photograph stains — helpful for repairs and insurance
More questions
Can a roofer fix a chimney leak?
A roofer can fix roof-related flashing, but many chimney leaks come from the crown, cap, mortar or brick — areas a chimney specialist should repair.
Need a professional?
Chimney Champs provides chimney waterproofing & leak repair across PA, NJ, DE, NY and CT. Call (856) 300-9215 for a free estimate.
Keep reading
- How Often Should You Clean Your Chimney?
- 9 Signs Your Chimney Needs Repair
- Chimney Inspection Levels 1, 2 and 3 Explained
- What Is Creosote? The 3 Stages and Why It Causes Chimney Fires
- What to Do in a Chimney Fire (and How to Prevent One)
- Chimney Liner Types: Clay, Stainless Steel, Aluminum and Cast-in-Place
- How to Get Your Fireplace Ready for Winter: A 10-Step Checklist