How to Inspect a Chimney Crown and Cap for Cracks and Water Entry
The top of the chimney is the part most often blamed on the flashing. Learn what a good crown looks like and what a failing one shows.
- Intermediate
- 30 to 60 minutes
- Updated
The short answer
A chimney crown is the sloped slab of mortar or concrete on top of the masonry. Check that it overhangs the brick by about 2 inches with a drip edge, slopes away from the flue, has no cracks wider than a hairline, and that the flue liner stands above it. A cap over the flue with a screen keeps out rain and animals. Crown repair and rebuilding is a mason's job.
When a chimney leaks, the flashing gets blamed first because it is the part you can see from the roof. But the crown on top is one of the most common sources, and it is the most neglected. It is a slab of mortar or concrete that caps the masonry, and every drop of rain that lands on top of the chimney lands on it. If it cracks, the water goes straight into the brick, then down the chimney and out as a ceiling stain that looks just like a flashing leak.
A quick inspection from the ground with binoculars, and from the roof if you can work tied off, will tell you most of what you need to know. This guide lists what a good crown and cap look like, what a failing one shows, and where a roofer stops and a mason starts. Use it alongside how to diagnose and fix a leaking chimney.
Tools
- Binoculars
- Flashlight
- Tape measure
- Camera or phone with zoom
- Straight ladder with stabilizer, or drone or roof access
Materials
- Notebook for findings
- Elastomeric crown coating, for minor hairline cracks, if a mason recommends it
- Stainless steel or galvanized chimney cap, as needed
Safety first
- Inspect from the ground with binoculars where you can. If you must go up, work tied off. WorkSafeBC requires fall protection at 3 metres (about 10 feet) and wherever a fall could cause serious injury.
- Never stand on or lean against a chimney. Crowns and top courses of brick can be loose and fall without warning.
- Make sure any fireplace, stove or appliance using the flue is off and cold before anyone works near the top of it.
Step by Step
Step 1: Look at the crown from a safe position
Look at the whole top of the chimney. The crown should be a continuous slab covering the full top of the masonry, not a flat mortar wash troweled on the brick. See whether the surface is rough, crumbling or missing in patches. A photo from the roof or a zoomed phone photo is useful for the records and for a mason's quote.
Step 2: Check the slope and overhang
The slope sheds water off the top. A crown that is flat or slopes toward the flue holds water. The overhang, commonly about 2 inches and tapered, lets water drip clear of the brick rather than running down the face. A drip groove cut into the underside stops water creeping back under the overhang. A crown that is flush with the brick is a weaker detail. The BC Building Code calls for the cap to slope away from the liner with a drip at least 25 mm (1 inch) out from the chimney wall, so about 2 inches gives a margin.
Step 3: Look for cracks and classify them
Hairline cracks, thinner than a credit card edge, are common in concrete and can be sealed with an elastomeric crown coating by a mason. Wider cracks, cracks that run along the edge of the flue tile, pieces missing and crumbling surface mean the crown has failed and will let water straight in. Cracks that continue down the brick mean the masonry itself is moving. Photograph and measure each one.
Step 4: Check the flue liner height and the gap
If the crown is built up to the top of the liner, or mortared solid to it, movement cracks it. The liner and the crown expand at different rates, so a flexible joint is the usual detail, and the BC Building Code calls for a cast-in-place concrete cap to be separated from the liner by a bond break and sealed. The same code has the liner finishing 50 to 100 mm (about 2 to 4 inches) above the cap. Check the joint for cracks and gaps. A missing or cracked joint is a direct path for water to run down beside the liner.
Step 5: Inspect the cap and screen
A chimney cap covers the flue opening to keep rain out and often has a mesh screen to keep birds, squirrels and sparks out. Stainless steel lasts longest, and galvanized rusts. Look for a cap that has shifted, bent, rusted or gone, and for a screen with holes. Without a cap, rain falls directly down the flue and onto the firebox or appliance. Mesh size and spark arrester requirements can depend on the appliance and local rules, so confirm them with a chimney professional.
Watch out: Do not cap or block a flue that is in use. A cap must let gases vent freely.
Step 6: Check the brick and mortar below the crown
The upper courses of a chimney take the most weather. Look for crumbling joints, missing mortar, bricks with flaking faces and white powdery deposits. If those are present, the water has been getting in for a while, and the repair is repointing and possibly rebuilding the top courses before the crown is redone.
Step 7: Decide what you need: coat, repair, rebuild or cap
Hairline cracks alone: a crown sealer applied by a mason. Wide cracks, missing pieces or no overhang: rebuild the crown. Missing or rusted cap: fit a new stainless steel cap. Loose brick or crumbling joints: repointing or rebuilding the top courses. All of this is masonry work. A roofer handles the flashing and the roof, and will tell you when the crown is the likely leak source. See how to reflash a chimney during a reroof for scheduling the work together.
What a Good Crown Looks Like
- Material: poured concrete or a cement mortar mix, reinforced where large, not a thin mortar wash.
- Overhang: about 2 inches past the brick on every side, with a drip groove or tapered edge.
- Slope: away from the flue, enough to shed water quickly.
- Liner joint: flexible sealant between the crown and the flue liner, which stands above the crown.
- Surface: continuous, free of crumbling, with no cracks wider than a hairline.
Freeze-Thaw and the Fraser Valley
Water that gets into a cracked crown freezes and thaws through the winter, and every cycle widens the crack. A chimney that stays wet through a long rainy winter and then sees a cold snap is the classic case for spalling brick and failed crowns. Checking the crown before the rainy season, and again in late winter, catches small cracks early.
Common Mistakes
- Blaming the flashing for a crown leak. Water from the top of the chimney shows up as a ceiling stain that mimics a flashing leak.
- Covering a failing crown with roof cement. It does not bond to masonry and cracks again.
- A flat mortar wash instead of a crown. It has no overhang, no slope and cracks quickly.
- Mortaring the liner solid to the crown. The two move differently and crack at the joint.
- Capping a flue that is in use. Never cap or block a flue in use.
- Climbing the chimney to inspect it. Use binoculars or a safe tied-off position.
When to Call a Professional
A roofer can inspect the crown from the roof and tell you whether it is the likely source of a leak, but crown repairs, repointing, brick replacement and flue liner work are a mason's or chimney professional's job. Wood and gas appliance flues should be inspected by a qualified chimney sweep, WETT inspector or gas fitter.
Loose or leaning masonry at the top of a chimney is a safety issue. Keep people clear and get it assessed promptly.
Fraser Roofing does free roof inspections across the Fraser Valley, from Hope to Abbotsford. See our Roof Repair service or the towns we cover.
How to Inspect a Chimney Crown and Cap: Questions
What is a chimney crown?
A chimney crown is the sloped slab of mortar or concrete that caps the top of the masonry. It sheds rain off the chimney, and it should overhang the brick by about 2 inches with a drip edge underneath. The flue liner stands above it. A cracked or crumbling crown lets water into the brick and down the chimney.
How do I know if my chimney crown is cracked?
Look from the ground with binoculars or photograph it from the roof. Cracks across the top, crumbling surface, pieces missing and gaps around the flue liner are signs of failure. Hairline cracks are common and can often be sealed, while wide cracks mean the crown needs repair or rebuilding by a mason.
Is a chimney cap necessary?
A cap over the flue keeps rain, birds and animals out, and often carries a screen against sparks. Without one, rain falls straight down the flue. Stainless steel caps last longest. The right cap and mesh depend on the appliance and local rules, and a flue in use must always be able to vent freely.
Can a cracked crown cause a leak inside the house?
Yes. Water enters through the cracks, runs down the inside of the masonry and appears as a stain on the ceiling or chimney breast that looks like a flashing leak. It is one of the most commonly missed causes of a chimney leak. A sectioned hose test, finishing with the crown and cap, will identify it.
Related Guides
All Chimneys guides|The full How-To Library
This guide is general education. Always follow the product manufacturer's installation instructions, the BC Building Code and WorkSafeBC requirements, which take priority over anything written here.
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