Chimney rain Cap & Chimney Cap/Crown Choices, Installation, Inspection, Defects, Repairs
     

• CHIMNEY CAP & CROWN - Definition of chimney rain cap; definition of chimney cap / chimney crown & chimney pot - different jobs of chimney rain cap vs. chimney crown/cap; Photo guide to types of chimney rain caps, chimney caps/crowns, other chimney top designs; Chimney rain cap defects; Chimney crown/cap defects ; Chimney caps & crowns: building codes & standards; Decorative chimney rain caps
• CHIMNEY INSPECTION at ROOFTOP - separate article, topic home
• BLOCKED CHIMNEY FLUES
• CHIMNEY CAP & CROWN - separate article
    Missing Chimney Rain Cap
    Damaged Masonry Chimney Cap or Crown
    Masonry Chimney Top Damage
    Separation of Chimney Flues - Chimney Top
    Soot at the Chimney Top
    UNLINED FLUE INSPECTIONS
• CHIMNEY CHASE - separate article
• CHIMNEY SHROUD FIRE - separate article
• CHIMNEY CRACK DIAGNOSIS - separate article
• CHIMNEY FLASHING Mistakes & Leaks - separate article
• CHIMNEY SHROUDS - separate article
• CHIMNEY SHOULDER LEAKS - separate article
• CHIMNEY SPALLING - separate article
• MASONRY CHIMNEY TOP DAMAGE - separate article
• SOOT at CHIMNEY TOP - separate article
• FIREPLACE INSPECTION PRE-FAB - separate article
• Questions & Answers about types of chimney rain caps & chimney caps / chimney crowns & their inspection, installation, troubleshooting & repair or replacement.
• References

Click to Show or Hide Related Topics

Also see Chimney Inspection Outdoors at Rooftop for a summary of chimney inspection points at the rooftop.

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.

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).

Metal chimney caps: the top of a wood-framed boxed-in structure through which a metal or insulated metal flue is routed must also be sealed against water using a chimney crown or cap, and the flue that extends through the chimney crown/cap also needs a rain cap. (Illustrated 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 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's sketch shows (left), 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.

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.

• 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 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

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:

• 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

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 Exterior 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:

• The fireplace damper has been rusted away, damaged or lost and the owner wanted to stop winter heat loss through the flue.
• The fireplace is not in use and the owner wanted to keep animals and/or rain out of the chimney flue

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.

At 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 Exterior Spalling

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.

Wrong. 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.

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 at Chimney Top & Clay Flue Tile Repairs.

Carson Dunlop's sketch 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. [24]

Our photo (left) illustrates a pair of metal chimney pots installed atop a brick chimney in Boston, Massachusetts.

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 (C) DJF.

These chimney pots, also located on a Boston MA building, illustrate a crowded, possibly multi-flue chimney serving multiple apartments in a building. These chimney tops and pots are touching, crowded, some not even vertical, raising a several worries:

• Do the individual flue drafts interfere with one another?
• Are there leaks around the base of the non-vertical chimney pots in this photo?

Either of these may in turn lead to unsafe chimney flues.

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. [5][35]

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 (left) provided courtesy of Chimney King. [5][35]

• [5] Stephen Werner, General Manager, Chimney King LLC., P.O. Box 8, Gurnee, IL 60031, Tel: (847) 244-8860, Email: steve@chimneyking.com, Website: www.chimneyking.com . Mr. Werner is also a licensed home inspector serving clients in Wisconsin. Chimney King sells their products through a network of fireplace dealers, chimney sweeps, roofers and builders. Each decorative shroud is custom built because no two chimney/chase are alike.

• The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
  
  Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.

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