I get frequent calls from clients about leaks around their chimneys. More often than not, the culprit is the roof flashing — sheet metal that keeps the intersection of the chimney and the roof watertight. When water gets behind faulty flashing, it can damage the roof sheathing, framing, and the ceiling below, so it needs to be dealt with immediately.
Before I get started, here’s a quick video on repairing flashing around a chimney.
Flashing Design and Materials
Proper flashing around a chimney includes two layers. The first is called step flashing — sections of L-shaped sheet metal are woven into the shingle courses and lapped up the side of the chimney. Next comes the counterflashing — a second layer of metal is embedded in the chimney mortar joints and folded down to cover the top of the step flashing.
The corners are especially vulnerable on chimney flashing. The sheet metal must be carefully cut and bent around the corners, often leaving a small gap that should be sealed with a high-quality urethane caulk. Over time, this caulk can dry out and detach, allowing water to seep in behind the flashing.
There are several types of metal used for chimney flashing, depending on climate:
These are common in most climates. These metals hold up well in heat, humidity, and moderate cold.
Copper is the longest-lasting option and the most expensive, so it’s mostly seen in high-end jobs or historic homes. Copper offers the advantage of soldered corners for a watertight seal.
Leak flashing is sometimes used because it’s pliable and simple to bend into shape. However, lead can be toxic if not handled properly.
Stainless steel is also quite durable, although more expensive than aluminum or galvanized steel. The advantage is excellent corrosion resistance.
No matter the material, proper layering technique is critical to keep water out of the vulnerable chimney–roof intersection.
Inspections and Maintenance
Because chimneys have so many potential leak points, I recommend inspecting the flashing and masonry at least every other year. Look for the following trouble signs:
- Loose, curled, or missing sections of flashing
- Cracks or missing mortar in the brickwork that can allow moisture penetration
- Signs of water damage, such as rotted sheathing under the shingles
- Rust stains on the chimney or roof
Cracks in the masonry can be repaired with flexible caulking designed for the purpose. I also suggest resealing brick chimneys every few years using a silicone-based water repellent applied with a garden sprayer. This helps prevent moisture from seeping into porous brick.
For detached flashing, the solution is removing and replacing the affected sections or possibly the entire flashing system if the damage is extensive. I generally prefer to replace the entire system, even if only one part is bad. It gives the client more peace of mind and allows me to properly guarantee my work.
Chimneys at the bottom of a roof slope should have a cricket — a small sloped roof structure that diverts water away from the chimney’s upslope side. The cricket should be completely covered with roofing membrane before shingles are installed. This adds another layer of leak protection.
Hiring a Professional Roofer
While minor chimney flashing repairs are doable for a handy homeowner, extensive issues are best left to a professional roofer. They have the skills, equipment, and experience to diagnose and fix chimney leaks for the long run.
Before hiring one, get multiple quotes and check references to find trustworthy local roofing contractors. Make sure they thoroughly explain the required repairs and provide a detailed written estimate.
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So, Is Leak-Proof Flashing Around Your Chimney Important?
Proper flashing is critical for keeping the vulnerable chimney–roof intersection watertight. Deteriorated, improperly installed, or missing flashing can allow torrents of water into your attic and walls, leading to expensive structural and interior damage. Regular inspections and prompt repairs of any issues are key to avoiding major chimney leak headaches down the road. Don’t ignore early warning signs like rust stains or damaged shingles around the chimney. Addressing problems early is always the wisest and most cost-effective approach.
FAQs About Chimney Flashing Repairs
With quality materials and workmanship, flashing should last 15 to 50 years, depending on the material. All flashing will be assessed by a contractor when your house is re-roofed. They’ll inform you if it needs replacing.
If the chimney masonry is undamaged, a roofer can handle flashing repairs solo. But if the brickwork needs repointing or repairs, a mason will have to repair it before the roofers can flash it.
It depends on the state of the flashing, which will be assessed by the roofing contractor. In some cases, the flashing has to be replaced. In others, it doesn’t. I would trust the opinion of the contractor you hire.
You can try sealing small gaps with roofing cement as a temporary fix. But it likely won’t hold for long, so full flashing repairs should still be done as soon as possible.
Most flashing comes painted with a protective coating, so painting it yourself isn’t usually necessary. For bare metal flashing, you can if you want to, but you don’t need to. Metals like lead or galvanized steel left bare for flashing are naturally weather-resistant.
