Crown vs. Cap: What's the Difference?

The two parts side by side

What a crown does and how a good one is shaped

Brick and mortar are porous. If the top of the chimney were left open, every rainstorm would soak straight down into the wall. The crown is the roof of the chimney. It covers the top course of brick and slopes away from the flue so water runs off.

Masonry industry guidance from the Brick Industry Association describes several features of a well-built top:

• Overhang with a drip edge, so water falls clear of the brick face instead of running down it.
• Slope away from the flue liner toward the edges.
• A bond break between the crown and the brick, so the two can expand and contract without cracking each other.
• A flexible sealed joint where the crown meets the flue liner, rather than a rigid mortar joint. Clay liners and concrete crowns move differently with heat, and a rigid joint tends to crack.
• The liner projecting a few inches above the crown surface.

Many chimneys have a mortar wash instead: a thin layer of mortar troweled over the top bricks, sloped toward the edges, with no overhang. Washes are common and they do shed some water, but they are thinner and tend to crack sooner than a properly formed crown.

What a cap does

A chimney cap sits on top of the flue, above the crown. A typical cap has three pieces: a base that clamps to the liner or fastens to the crown, a mesh screen around the sides, and a solid lid on top.

• The lid stops rain and snow from falling straight down the flue. Water inside a flue rusts dampers, stains fireboxes and can mix with soot to create odors.
• The screen keeps birds, squirrels and raccoons from moving in and keeps leaves out. It also catches larger embers.
• The overall shape can reduce the effect of wind blowing across the flue top on some chimneys.

A trade article from the Mason Contractors Association of America notes that screen opening size varies by region and that very fine mesh can clog with soot more quickly. That is one reason screens are checked during sweeping. A clogged screen can restrict the flue the same way a nest can.

Caps come in two main styles. A single-flue cap fits over one clay liner that sticks up above the crown. A multi-flue or crown-mount cap covers the whole top of the chimney and is fastened to the crown. The right style depends on how many flues there are, how far the liners project and what appliances vent through them.

Why one does not replace the other

A cap does not stop water from soaking into a cracked crown. The lid is above the flue, and the crown around it still gets wet. A crown-mount cap can shelter part of the crown, but it does not repair cracks underneath.

A crown does nothing for the inside of the flue. Rain and animals still drop straight down an uncapped flue.

Some products blur the line. A chase cover on a factory-built chimney is a metal pan that does the crown's job on a framed chase. A top-sealing damper combines a cap and a damper in one unit. If your chimney has one of these, the same logic applies: something has to shed water off the top of the structure, and something has to protect the flue opening.

Looking at your own chimney from the ground

You do not need to climb on the roof to learn a lot. Stand back far enough to see the top of the chimney, and use binoculars or a phone camera zoom.

• Look at the very top edge of the brick. A crown with an overhang shows as a thin gray band that sticks out past the brick on all sides. A wash usually sits flush with the brick or slightly inside it.
• Look above that band. If you see a square or rectangular clay tile sticking up with a metal box or screen on it, that is a single-flue cap. A large metal box covering the whole top is usually a multi-flue cap.
• Count the openings. Two or three tiles usually means two or three flues, each serving a different appliance.
• Check the color of the brick near the top. Dark streaks, white bloom or missing brick faces near the crown suggest water has been getting into the masonry.

Please do not walk the roof to check. Pitch, wet shingles and height make it dangerous, and a closer look is part of a normal inspection.

Clues that one of them needs attention

These are things homeowners notice. They are reasons to have the top of the chimney looked at, not proof of a specific problem.

• Pieces of concrete or mortar on the roof or in the gutter near the chimney.
• Water or rust stains on the damper, firebox walls or hearth after rain.
• Animal sounds, nesting material or a strong odor from the fireplace.
• A cap visibly tilted, rusted through or missing after a storm.
• Staining or white deposits on the upper part of the brick. See White staining on brick.

Water inside the house can come from the crown, the flashing, porous brick, the cap or the roof itself. Telling them apart takes a closer look. When the source is unclear, we use controlled water testing to narrow it down.

Repair options in general terms

Crowns. Small hairline cracks on an otherwise sound crown are often sealed or coated with a product made for crowns. A crown that is badly cracked, broken off at the edges, flat or built without overhang usually needs to be rebuilt. The choice is covered in Crown coating vs. crown rebuild, and the service is described on our chimney crown repair page.

Caps. A loose cap can sometimes be refastened. A rusted, damaged or wrong-size cap is usually replaced. If there is no cap at all, adding one is a simple upgrade for most masonry flues. See chimney caps.

Before either job, the flue and the top of the chimney are checked. There is no point capping a flue with a cracked liner or recoating a crown sitting on loose brick without knowing about it first.

Questions homeowners ask

Sources

1. Brick Industry Association, Technical Note 19B: Residential Chimneys, Design and Construction (archived PDF copy)
2. Masonry Magazine (MCAA): Installing the correct chimney cap
3. CSIA: Level 1 inspection checklist, masonry chimney (PDF)

This guide is general information. It can't diagnose a specific chimney; an inspection can.