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.

Chimney Cap or Chimney Crown Inspection Guide & Defects

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 - see those

details at CHIMNEY POTS & DECORATIVE TOPS

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 RAIN CAP / RAIN COVER INSPECTION

Chimney Cap / Chimney Crown Defect Inspection Checkpoints

Chimney crown/cap slope

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

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

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

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.

• Here is a chimney with a mortar cap or "chimney cap" but with no rain cap.
• Chimney flues terminating at same height:
  
  the design would have been better if one of the clay flue liners projected several inches (4"-6") higher than its neighbor, and if the concrete cap had been pre-cast or otherwise constructed to give an overhang past the sides of the chimney so that runoff would not wet and damage the brick masonry below.
• Missing expansion joint at chimney flues: installation of this chimney cap would also have been better if there were an expansion gap and sealant permitting the flue tiles to expand without cracking the surrounding concrete cap.
• Cracking chimney cap: also notice that the chimney cap, though recently installed, is cracking.
• Missing chimney cap drip edge: also notice that the chimney cap does not extend past the sides of the chimney, inviting water and frost damage;
• Too thin chimney cap: this chimney cap is thinner than the MIA recommended minimum of two inches.

Complete omission of chimney cap / crown / top seal

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.

Crowded chimney tops, flues, & rain caps

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:

• The lack of a true drip edge around the chimney top has led to damaged brick work - as you'll see from the concrete "repair" smeared around four courses of brick near the chimney top.
• The individual flues all terminate close together, at the same height, inviting cross-communication, downdrafts, and draft interference
• The omission of an expansion joint around each flue tile, (or bad mortar mix) may explain the repeated attempts to patch cracks in the chimney top cap using roofing cement or tar;
• Using the chimney to support an antenna is not recommended

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

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.

Also see CHIMNEY SPALLING

and see CHIMNEY REPAIR METHODS

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.

See CHIMNEY CHASE CONSTRUCTION
and also

see CHIMNEY SHROUDS used at the top of chimney chases.

 

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

Question:

(Dec 3, 2014) Tony said:
We installed a triple walled metal chimney 12'run of pipe straight up from the top of our woodstove to 3' above the roof line. We burn our stove almost constantly at 250F-400F.We don't see any creosote buildup when inspecting and cleaning the chimney, but are plagued by soot collection in the top 3'-5' of the chimney. There is no chase surrounding the exposed section of the chimney, would an insulated chase eliminate this problem? Or are there other solutions? I'm getting too old to keep climbing up on the roof all winter.

Reply:

Tony I'm not confident I can safely diagnose and recommend for this concern. Light soot from a woodstove at a chimney top may be ok but if soot blocks the cap, screen or flue there are indeed safety hazards. I agree that depending on the chimney height, enclosing the flue increases its temperature - but in wood burning I'm not sure what that does to soot at the cap.
I would feel that you are safest getting onsite advice from a certified chimney sweep. Do keep us posted.

Question:

(Feb 2, 2015) Eva said:
Do you need licence to produce Chimney caps in nyc?

Reply:

I'm not sure Eva, if you need a special license to produce chimney caps but selling them would be another question: certainly you'd need to get your chimney caps listed by UL or another accepted authority before they'd be code-approved and thus legal to install.

Question:

30 March 2015 chris said:
what is the minimum clearance between the top of the flue liner and the bottom of the chimney cap

Reply:

Chris this question was answered just below in a reply to ANON - thanks for asking, I'll also add that text to the article above.

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

Or see these

Chimney Top Cap, Crown, Rain Cap Articles

• CHIMNEY INSPECTION DIAGNOSIS REPAIR - home
• CHIMNEY CAP / CROWN CONSTRUCTION
• CHIMNEY CAP & CROWN DEFINITIONS
• CHIMNEY "CAP" CROWN / TOP SEAL INSPECTION
• CHIMNEY INSPECTION from GROUND
• CHIMNEY INSPECTION at ROOFTOP
• CHIMNEY RAIN CAP / RAIN COVER INSPECTION
• CHIMNEY RAIN CAP / RAIN COVER DIY
• CHIMNEY RAIN CAP VENT OPENING SIZE
• CHIMNEY POTS & DECORATIVE TOPS
• CHIMNEY SHROUDS
• CHIMNEY STAINS & LEAKS
• CHIMNEY TOP MASONRY DAMAGE
• FLUE SEPARATION REQUIREMENTS

Suggested citation for this web page

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

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to CHIMNEYS & FLUES

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Citations & References

In addition to any citations in the article above, a full list is available on request.

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