Chimney guides

Crown or Cap? Two Different Parts, Both Often Missing

These two get used interchangeably and they are not the same thing. On a lot of older Massachusetts chimneys, both are missing, and the two absences cause different problems.

A cast crown with a drip edge and a stainless multi-flue cap above it

Short answer

The crown is the masonry slab on top of the chimney, around the flue, and its job is to throw rain clear of the brickwork below. The cap is the metal cover with mesh sides that sits over the flue opening itself, and its job is to keep rain, birds and debris out of the flue and embers in. A chimney needs both. They are fitted in the same visit because the access is identical.

What the crown does and why the wash fails

A correct crown is a cast slab, reinforced, sloped away from the flue, with an expansion joint where it meets the flue tile and a projection past the brick with a drip edge cut underneath.

What most older houses have is a mortar wash troweled flush with the brick face — no reinforcement, no expansion joint, no overhang. Mortar and clay tile expand at different rates so it cracks around the tile within a decade, and with no overhang, water that gets through runs down the face of the brick rather than falling clear of it. That is what soaks the masonry, and soaked masonry in a Massachusetts winter spalls.

The overhang is the detail that matters

It sounds minor. It is the difference between water falling away from the chimney and water sheeting down it several times a year for decades.

What the cap does

Cheaper than almost any other chimney component and the highest value per dollar on the whole structure.

Keeps rain out of the flue

An open flue is a vertical pipe into the house. Rain goes down it and sits in the smoke chamber and firebox, rusting the damper and soaking the masonry from inside.

Keeps animals out

Birds and squirrels nest in open flues. A nest is both a blockage and a fire hazard, and chimney swifts are legally protected during nesting season, which affects when a flue can be cleared.

Arrests embers

The mesh sides stop burning fragments leaving the flue.

On a center chimney, one cap can cover the lot

A multi-flue cap spanning the whole crown protects the crown as well as the openings, and usually looks better on a colonial stack than four separate caps.

Why they are done together

Access is the cost. Getting a mason and staging to the top of a chimney on a steep slate roof is most of the price of either job, so doing one and coming back for the other roughly doubles what you pay.

There is a technical reason too. A new crown on a chimney with an open flue is protecting the structure from the outside while rain continues to go straight down the middle of it. The two components are halves of the same job.

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Frequently asked questions

Can I see whether I have a crown or a wash?

Not from the ground. It needs a look from the roof or a drone photograph. Water appearing inside in ordinary rain is the indirect sign.

Does a historic district have a view on caps?

Frequently, because a bright stainless cap on a colonial stack is conspicuous. Black powder-coated stainless is usually the compromise. Ask before ordering.

How long does a stainless cap last?

Decades, including on the coast. Galvanized might give five to ten years inland and considerably less near salt water.