Chimney caps & crowns: this article describes the types of covers & terminations found at the top of chimneys and flues. We define chimney rain cap, chimney cap, chimney crown, and chimney pot, giving photo-examples of each of these components.
We illustrate common chimney cap & crown types, choices, & defects, and we cite pertinent chimney top cap / crown building codes & standards for fire and other safety concerns.
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Some of us are confused about what to call the topmost components of a chimney. For clarity in this article, unless we state otherwise here is what we mean by "rain cap", "chimney cap", "chimney crown" and "chimney pot".
Definition of Chimney Rain Cap
A chimney rain cap is a rain cover on top of a chimney flue designed to keep out rain (which can damage the flue or appliances it vents) and intended to reduce downdrafts in the chimney in windy conditions.
Some chimney rain caps may be supported atop a masonry chimney in a position to shelter the chimney flue, and may not only cover the chimney flue opening but may also project out beyond the entire chimney top (red arrow, photo at left).
This example is still a chimney rain cap.
[Click to enlarge any image]
On many clay flue tile lined chimneys the rain cap will mount directly on to and will cover only the chimney flue itself (photo at left).
A retrofit chimney rain cap is shown in our photo.
This rain cap is designed to fit over the top of a standard sized clay chimney flue tile and is held in place by four threaded bolts that press against the sides of the flue tile.
Other chimney rain caps for clay tile flues mount by friction by insertion into the interior of the top of the flue tile.
Watch out: over tightening the securing bolts of this chimney rain cap can break the flue tile, while leaving them too lose risks that the whole rain cap assembly blows away during high winds.
Definition of Chimney Cap = Chimney Crown = Mortar 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).
Watch out: leakage into a chimney through a defective chimney cap leads to damage to the chimney structure, chimney flue, and leads to interior leaks as well as unsafe conditions.
Our photo of a metal chimney cap and rain-cap combined in a custom-fabricated design (at left), adds more confusion to chimney top terminology. This chimney was observed atop a hotel near Bar Harbor, Maine.
Definition of Chimney Pot
As we illustrate in more detail below at DECORATIVE CHIMNEY POTS, the term "chimney pot" is used to describe a decorative rain cap assembly on the top of a chimney, covering its flue and in some cases covering both the flue itself and the entire chimney top, including the chimney flue and chimney cap/crown.
Typically the chimney pot also adds height to the top of the chimney flue.
Our chimney pot photo (left) illustrates a retrofit or add-on chimney pot that increases the effective chimney height of a concrete block chimney, possibly aiding in solving a chimney draft problem.
Also see CHIMNEY HEIGHT EXTENSIONS.
The Chimney Rain Cap Has A Different Job From the Chimney Cap/Crown
The purpose of the chimney cap/crown [chimney crown] is to close off the space between the flue liner and chimney wall, to shed water clear of the chimney and generally prevent moisture entry.
The chimney rain rain cap has the job of keeping rain and wind down-drafts out of the chimney.
Some rain caps also include a screen that functions as a spark arrestor to reduce the chances of a spark exiting the flue to land on and set afire a nearby roof surface or other materials.
The rain cap or hood shown in the sketch at left is charged with preventing sparks from leaving the chimney - a fire safety measure.
Sketch courtesy Carson Dunlop Associates.
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's 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.
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
This chimney 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.
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:
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
Watch out for Sealed-off Chimney Tops & Flues
As we illustrate in our photo at left, there are two concerns at this stone-faced masonry chimney.
1. The smaller chimney flue, typically venting heating equipment, has received a retrofit rain cap that may not permit adequate draft - note that the cap top is quite close to the top of the clay chimney flue tile upper surface.
2. The larger chimney flue, probably venting a fireplace, has been closed or capped-over using a single solid piece of stone or slate. Why would someone do this? Some common explanations for this chimney top seal include:
Watch out: we often find a temporarily capped-off fireplace flue or unused chimney flue that was left in that condition by a prior building owner. The new owner, attempting to use the chimney before its safety and condition have been determined, faces risk of being driven out of the home by smoke at a fireplace or worse, potentially fatal carbon monoxide poisoning if the flue is to be used by a heating appliance.
Also see MASONRY CHIMNEY TOP DAMAGE.
At above left we illustrate another "sealed-off" masonry chimney.
Located atop the Justin Morrill Smith historic home in Strafford Vermont, this brick masonry chimney has been capped-off with a metal cover. The chimney is no longer in use and preservationists wanted to protect the chimney interior and exterior from leaks and from further frost damage.
At the chimney's left corner as well as in smaller areas below you can see evidence of severe frost related spalling of its brick surfaces.
Also see CHIMNEY SPALLING
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.
The most common defect we observe at chimney rain caps is that there is none - the rain cap was never installed, or it has been lost or blown away. Below, photographs of two types of factory built metal chimneys illustrate the loss of the chimney's rain cap. At below right you can also notice water ponding around the chimney flue.
If we want proof that people don't spend a lot of time looking at their chimney, ask a home inspector or chimney sweep how often they find that the rain cap or spark arresting chimney cap has been completely lost from a chimney.
As our photographs illustrate, a missing cap invites water damage to the chimney and the equipment it vents, draft problems (no protection against downdrafts caused by some wind conditions), and unsafe operation.
Water entering the chimney can cause enough corrosion in a metal flue that the chimney needs replacement.
Water entering the chimney also risks corroded leaky flue vent connectors, leading to draft problems and carbon monoxide poisoning risks as well as costly or dangerous damage to the heating equipment itself.
Damaged or Defective Metal Rain Caps on Chimneys
Leaks at damaged factory-built chimney rain cap
The insulated metal chimney rain cap shown at left was installed on a New York home by a Hudson Valley chimney company whose owner thought we were being picky and fussy to complain about the smashed rain cap top surface.
The rain cap top cover is secured by a wing nut screwed to a bolt that protrudes through the cap top surface. The concave surface of this damaged rain cap would guarantee water leakage down the metal chimney and into the heating appliance it serves, inviting rust damage and potentially leading to costly repairs or even unsafe equipment operation.
A "field repair" of a blob of silicone around the wing nut reduces the leakage rate. The proper repair is to remove the rain cap, restore its original domed shape, and reinstall it, or replace it with a new one.
In our photo at left, the interesting chimney has a metal rain cap on one flue and not the other. The metal chimney cap looks home-made and perhaps not functional. The un-covered chimney flue (and most likely the covered one) are comprised of hard-fired clay chimney flue tiles.
The presence of creosote tar and soot stains around the left-hand rain cap and the size of its base make us suspect that what was originally a fireplace flue was covered and possibly lined with a smaller-diameter metal flue serving a woodstove.
Watch out: without disassembly or an in-flue inspection we don't know if this chimney has been lined with a metal flue, insulated, safe, and proper, or not. Further clues will be found indoors, such as perhaps a woodstove or fireplace insert. Further in-flue inspection for chimney safety is needed.
Rust Damaged chimney cap / crown / top seal and rusty chimney rain cap
This chimney may have been "re-lined" (maybe) using a rust-prone metal flue, and like an earlier metal chimney liner shown in this article, this flue is of unknown and possibly suspect condition.
A metal chimney cap covers the entire original brick masonry chimney, a metal flue extends through the cap, and a metal rain cap tops the flue.
All of these components are rust damaged and may be perforated or unsafe. This chimney installation is at risk of leaks, damage, unsafe conditions.
Watch out for "faux brick" metal chimneys and flues such as the factory built metal chimney shown at left. This chimney, glanced-at quickly from ground level from the other side of the house, might be mistaken for a clay tile lined brick flue with a metal rain cap.
This is an all-metal factory-built chimney. And inspecting from the opposite side of the home one can observe rust stains that raise the concern for a rust-perforated, damaged chimney structure, wall, or flue.
Looking closely at the bottom left of the chimney cap you can see a spot of daylight (red arrow) - this chimney cap has rusted away, risking damage to the flue and to the heating appliance.
Non-Listed Chimney Rain Cap Hazards
This chimney is capped by having inserted a short length of metal flue with a riveted rain cap attached. The whole assembly slides down into the flue, blocking adequate flow of exhaust gases from the gas fired heater being vented.
We suspect that this little rain cap is not listed for this application and that the chimney is unsafe.
Our measuring tape is also indicating the distance to the nearest roof surface - the chimney also lacked adequate height above the nearest roof surface.
Rust Damaged Chimney Turbine Vent or Turbulator Vent Cap
This chimney is capped by a turbine vent or turbulator chimney cap intended to improve chimney draft. In the presence of wind the spinning cap can increase chimney draft but its performance would thus be inconsistent.
We're not sure that a turbine vent provides reliable rain protection nor that this was a proper application for turbine vents.
[Research in process].
You will note that the installation is rust damaged as well.
Happily this chimney is no longer in use, so in this particular case the turbine vent and its rust are only a cosmetic issue - unless someone attempts to return the chimney and flue to service.
Damaged / Defective Masonry Chimney Rain Caps
A good rain cap or chimney cap (DF's terms) does more than keep out the rain; it also improves chimney draft and prevents downdrafts inside the chimney in windy conditions.
A masonry rain cap such as the one shown in our photo at left can be an effective chimney shelter if it extends past the sides of the chimney and if it is secure.
The chimney shown is a single-wythe flue in Brooklyn, NY. The above-roof section is about to collapse - the chimney is unsafe.
We discuss repairs to chimneys at the roof top
Site-Built Brick Chimney Rain Caps & Chimney Caps: Combination Designs
At below left we illustrate a simple masonry chimney cap and rain cap constructed using thin soft clay bricks.
This combined rain cap and chimney cap and serve adequately to keep most rain out of the flue. Built originally for venting a small wood fire, this chimney rain cap are located in the temperate climate of central Mexico. You can see minor damage to the chimney's drip cap as the soft bricks are easily broken away.
Below our photo illustrates a combined chimney rain cap and chimney cap constructed of arch brickwork atop a New Hampshire home.
Like the A-shaped Mexican chimney rain cap (above left) this New Hampshire arched chimney rain cap offer some rain protection for the chimney flue and top surface but these designs:
Chimney Cap Clearance From Flue: Chimney Cap / Screen Vent Opening Dimensions
Reader Question: minimum distance from chimney rain cap to top of flue
(Nov 8, 2012) Devon Bowman said:
Minimum chimney cap vertical cap bottom edge to flue upper edge clearance distance as described below is described by the cap manufacturers we surveyed as 5". Less may restrict chimney draft.
CHECK with your local state or provincial fire and chimney code and your building department as different specifications may apply where you live. Some states are silent on this detail: For example in New York State see Title 27 / Subchapter 15 Chimneys and Gas vents you'll find "[1501.10] 27-865 Chimney caps silent on dimensions.
I think the reason this particular clearance distance has not come up is that factory rain caps for metal flues are pre-fabricated - one would not modify that device and it would provide its own clearance by its design. This is true for UL-Listed pre-fab chimney caps that fit into masonry flues as well. The typical manufacturer's / distributor's chimney cap measurement instructions for ordering address the flue inner dimensions into which the cap mounting sleeve must fit (for non-extended flues) or the flue's outer dimensions (for extended flues) over which the cap sleeve fits.
Typically manufacturers who discuss the vent opening refer to the actual effective opening - which is more important than the actual distance about which you asked, as the chimney cap screen height.
Watch out: The required screen height is really the actual opening availalable for venting, and this height may need to be further adjusted depending on the screen mesh opening size as that in turn also obstructs venting both on its own and by its tendency to collect soot and debris (smaller mesh means faster clogging and more obstruction).
Watch out: a chimney cap is usually described just by the dimensions that fit the flue size - the actual screen height or venting area is often not given.
Again, look for AT LEAST 5" of vertical screen opening height. This is not quite what you asked but it's the best reply.
OPINION: I would like to see the greater of 5" unobstructed vertical screen opening height or for larger diameter chimney flues, a vertical opening height that equals the largest flue top horizontal opening (for rectangujlar flues) or its diameter (for round flues). And that opening may need further adjustment for smaller mesh screen openings that obstruct draft.
Watch out: we also don't want an excessive vertical cleareance distance between the top of the flue opening and the lowest portion of the chimney cap cover, since if the opening were too all the rain cap no longer does a good job keeping rain out of the flue.
Safety warning: use only a listed chimney cap on your chimney flues.
Our photo (above left) of a Boston Massachusetts chimney top and Carson Dunlop Associates' sketch at above right illustrates a typical chimney pot design, a decorative treatment used at the top of (usually masonry) chimneys.
A chimney pot is often cast of concrete or constructed of fired clay in a decorative design as we illustrate further below.
What is not clear in the Carson Dunlop sketch but what you will see in our photographs below, is that most decorative chimney tops, caps, or crown assemblies cover the flue and include rain cap protection as part of their design.
Also see Ceramic Roofware in our references section at the end of this article. 
From the ground we cannot ascertain the condition of the rain cap, actual flue vent opening, nor how well the chimney crown/cap is sealed around this pair of metal chimney extensions.
Our photo (left) of decorative custom-cast concrete chimney pots or decorative chimney crowns (in some people's usage) illustrates the combination of rain-cap and complete chimney flue and crown covering offered by chimney pots designed by Gaudi and found on the top of the Gaudi apartment house in Barcelona, Spain.
Those "eye' shaped openings visible in these decorative chimney crown assemblies are the actual vents, while a domed top offers rain protection for the chimney flue.
The decorative chimney top design used here overhangs the entire chimney side, providing good drip-edge protection for the chimney top and sides. - Photo ©DJF.
Either of these may in turn lead to unsafe chimney flues.
Warning About Installing Decorative Chimney Top Shrouds (Chimney "Crowns") on Factory-Built Chimneys
Watch out: installing a decorative chimney pot or chimney crown on a factory-built chimney may be unsafe as well as a building code violation.
Unless the decorative chimney shroud or "crown" is listed and labeled for use with the specific factory-built chimney system where it is installed there is a risk that the added decorative covering can cause overheating, leading to a roof or chimney chase fire or other unsafe conditions such as inadequate draft.
- Thanks to Stephen Werner, Chimney King LLC in Gurnee, IL, for this warning. 
Details about decorative chimney top shrouds ("crowns" among some installers) installed atop wood-framed chimney chaseways, including model building code citations and fire safety warnings, are at CHIMNEY SHROUDS. Also see FIREPLACE INSPECTION PRE-FAB.
Photo of a listed decorative chimney top shroud (above left) provided courtesy of Chimney King. 
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Frequently Asked Questions (FAQs)
(Dec 3, 2014) Tony said:
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.
(Feb 2, 2015) Eva said:
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.
30 March 2015 chris said:
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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