Photograph of a cracked chimney top crown and no cap installed.Chimney Chimney Cap/Crown Inspection & Defects
Masonry Chimney Top Seal, Inspection, Defects & Repairs

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Chimney caps & crown inspection procedures:

This article describes common chimney cap & crown types, choices, & defects, and in the article REFERENCES section we cite pertinent chimney top cap / crown building codes & standards for fire and other safety concerns.

Shown at page top: a cracked concrete chimney cap or crown around two clay flue tile liners that are both a bit short and that both lack a chimney rain cap.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Chimney Cap or Chimney Crown Inspection Guide & Defects

Photograph of a damaged masonry chimney. at CHIMNEY CAP & CROWN DEFINITIONS we explained that what experts mean by "chimney cap" or "chimney crown" or "chimney top seal" on masonry flues is the seal around the flue protruding through the top of the masonry chimney.

Here we repeat that definition and then list common defects found at the chimney cap.

Masonry Chimney Caps: on a masonry chimney the chimney cap is a pre-cast concrete or poured in place concrete seal around the flue tile (on a modern masonry chimney). In our photo (at left) the chimney cap, also called a mortar cap, is the gray concrete visible around the projecting flue tiles at the top of the chimney.

This particular chimney cap is defective: too thin, cracked, leaky, missing an expansion joint at the flue tile, and lacking a drip edge projection over the chimney top.

The Masonry Institute of America calls this chimney top surface seal around the flues the chimney cap. We're following their terminology.

Others call this area the "chimney crown" in an effort to avoid confusion between the chimney cap (red arrow) and the chimney rain cap (blue arrow). To add confusion "chimney crown" is used by others to refer to decorative chimney tops or pots (described below).

If you need information about the rain cap found atop a masonry or metal chimney (the metal cap and steel mesh cover on the flue shown at above-left) and if you don't care a hoot about the concrete seal shown in the photo above, please see this separate article:


Chimney Cap / Chimney Crown Defect Inspection Checkpoints

Chimney crown/cap slope

Chimney cap slope (C) Carson Dunlop Associates

The chimney "cap" [or crown] should slope away from the flue at a good rate of about 3-inches per foot.

The chimney cap should not be bonded to the flue liner or top of the chimney in order to allow for thermal expansion of the liner. The space between the cap and the flue liner must be closed with a flexible sealant.

Mortar chimney "caps" are prone to cracks and allow water to drain over the face of the chimney masonry leading to spalling, loss of mortar and leakage to the interior spaces. Corrosion at the chimney base cleanout doors are common to those types of chimneys.

Check the chimney top for damaged masonry (or rusted metal), a missing cap, damaged, cracked, or missing top seal or crown on the top of a masonry flue, and here, an important discovery (at least in some jurisdictions) is whether or not the chimney is single wythe or thicker masonry and whether or not the chimney has (or perhaps needs) a chimney liner.

Chimney cap/crown drip edge

Chimney top missing drop edge (C) Carson Dunlop Associates The Brick Institute of America (BIA) recommends chimney caps of pre cast or cast-in- place concrete a minimum of 2-inch thick with a projection of 2 1/2-inch beyond the face of the masonry surround so that water shed from the top will not run down the face of the brick.

The concrete chimney crown in our photo (above) is also referred to in many texts as the "chimney cap" but in this usage, "chimney cap" refers to the capping seal on the top of a masonry or certain other chimneys - a seal that surrounds the chimney flue but does not cover it.

In Carson dunlop Associates' sketch at left the chimney crown looks recently installed and does not drain past the chimney sides. There has been water damage covered up with painted metal on the chimney side facing us.

This chimney needs some safety inspection and probably new caps on the flues.

As Carson Dunlop Associates' sketch shows, a good drip edge at the chimney top cap helps reduce water and frost damage to the chimney sides and structure.

Watch out particularly for flat or even in-sloping metal caps on wood-framed chimney chases built around metal chimneys - these are often a source of hidden leaks into the structure and potentially dangerous rust or corrosion damage to fireplace inserts and flues as well as damage to heating equipment.

Chimney crown/cap damage or missing drip edge

Chimney top cap construction details (C) Carson Dunlop Associates

Carson Dunlop Associates [at REVIEWERS] sketch (left) show some details of good chimney cap construction. The object of these details is to avoid water and frost damage to the flue or to the chimney itself.

Chimney cap history: if a chimney has spent part of its life with no rain cap installed, or if the masonry cap is poorly constructed, there is extra risk of water damage to the flue interior.

In a masonry chimney damage may appear as frost cracking of the upper flue liners or masonry.

In any chimney, there may also be water damage to the heating appliances being vented by that chimney, such as rust, formation of corrosive condensate, or creosote.

Damaged Masonry Chimney Cap / Crown: cracks, missing pieces, leaks

Photograph of a cracked chimney top crown and no cap installed.

Chimney Cap defects

Shown here is the concrete seal around the top of a chimney, sealing the upper chimney surface around the projecting chimney flue (clay flue tiles in this photo) in order to close off the space between the flue liner and chimney wall, to shed water clear of the chimney and generally prevent moisture entry.

Complete omission of chimney cap / crown / top seal

Photograph of a damaged masonry chimney.

The chimney at above left has been "re-lined" (maybe) using a rust-prone metal flue of unknown but highly suspect condition, passed through a single wythe brick masonry chimney with no chimney cap / crown / mortar seal to keep water and weather out of the chimney. This is a poor chimney installation subject to leaks, damage, unsafe conditions.

Below, besides the absence of a rain cap, this is a scary unlined chimney flue we observed in Buenos Aires, Argentina. That pile of used bricks around the chimney also raises the question of whether or not other bricks dropped down into (and thus may be blocking) the chimney flue.

Open chimney top,  Buenos Aires Argentina (C) Daniel Friedman

Crowded chimney tops, flues, & rain caps

Photo of a crowded chimney top with several issues (C) Daniel Friedman

This chimney jams seven flues into one structure. The chimney rain caps are jammed together and the flues are so close that it was impossible to retrofit an add-on rain cap onto all of the flues. A better solution would have been a single rain cap covering all of the flues.

But this chimney top, located atop a New York building in the Hudson Valley, has other problems too:

Water & Frost-Damaged Chimney Tops - cracked, spalling masonry

Photograph of a damaged masonry chimney. Photograph of a damaged masonry chimney.

Damaged chimney caps / crowns / mortar caps are shown in our two photographs at left.

In both of these photographs you can also see that water (and in a freezing climate, frost) have damaged the brick masonry of the chimney itself.



Improper, Damaged Metal Caps / Crowns on Wood-Framed Chimney Chases

Our photos below illustrate common sources of leaks into the wood-framed chimney chase used for factory-built metal chimneys.

Poorly-supported metal covers over the wood-framed chimney chase lead to a concave or sunken top cap that leaks into the chimney assembly.

Damaged, concave, leaky chimney crown/cap seal on wood framed chimney chase (C) Daniel Friedman Damaged, concave, leaky chimney crown/cap seal on wood framed chimney chase (C) Daniel Friedman

and also

see CHIMNEY SHROUDS used at the top of chimney chases.


Continue reading at CHIMNEY RAIN CAP / RAIN COVER INSPECTION or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see FLUE SEPARATION REQUIREMENTS for vertical and horizontal separations needed in the flue and at the chimney top.

Or see these

Chimney Top Cap, Crown, Rain Cap Article Series Contents

Suggested citation for this web page

CHIMNEY "CAP" CROWN / TOP SEAL INSPECTION at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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Publisher - Daniel Friedman