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Squashed unsafe chimney rain cap (C) InspectAPedia TW Chimney Rain Cap Inspection
Chimney rain cap or top cover inspection, defects & repairs

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Chimney caps & crown inspection procedures:

This article describes the inspection of and common defects or hazards found at covers & terminations found at the top of chimneys and flues. We provide a checklist of chimney top or chimney rain cap defects for building owners, contractors, or inspectors.

This article sercies describes 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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Chimney Rain Cap Inspection & Defects Checklist

Metal raincap on chimney (C) D Friedman Chimney rain cap (C) Daniel Friedman

At above left is a typical metal rain cap atop a masonry flue; rain caps are also found atop metal chimneys and flues. At above right is a flat stone rain cap over a stone masonry chimney.

[Click to enlarge any image]

Definition of Chimney Rain Cap or Rain Cover

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 above left).

If you are concerned about the cap or crown seal around the chimney flue where it projects through the chimney top of a (usually) masonry chimney and don't care about the rain caps shown above, see this
article CHIMNEY "CAP" CROWN / TOP SEAL INSPECTION.

Chimney Rain Cap / Rain Cover Inspection Guide to Defects

The Chimney Rain Cap or Rain Cover Has A Different Job From the Chimney Cap/Crown

Chimney cap and spark arrestor (C) Carson Dunlop Associates

The chimney rain rain cap (also defined at CHIMNEY RAIN CAP DEFINITION ) 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.

Below we list chimney rain cap or rain cover inspection points and common defects and hazards.

The purpose of the chimney cap/crown  [chimney crown] described at CHIMNEY CROWN TOP SEAL DEFINITION 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.

Blocked Chimney Flue at Chimney Top: Squashed Cap or Animal Nests

Chimney top blocked by a stork's nest in Rabat, Morocco (C) Daniel Friedman Squashed unsafe chimney rain cap (C) InspectAPedia TW

At above left, the chimney top is completely obstructed by a stork's nest. This chimney, located in Rabat, Morocco, was not in use when we took the photo.

Mechanical damage, birds or squirrels can all render a chimney inoperative and unsafe. The immediate hazards include fatal carbon monoxide poisoning or a building or chimney fire, while more subtle hazards from a partly-blocked chimney include improper heater operation.

A squashed chimney rain cap can also block the flue - see the photo of the round rain cap and flue at above right.

See CHIMNEY RAIN CAP OPENING SIZE for an example of the trouble caused by a rain cover that does not provide adequate flue vent opening area.

Other examples of chimneys blocked by the rain cap or spark arrestor

Metal raincap on chimney (C) D Friedman

A retrofit chimney rain cap is shown in our photo at above left. 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: when installed over a flue used to vent a wood-fired burning appliance such as a wood stove or a wood-burning fireplace, creosote can condense on and quickly block the mesh of the spark arrestor, leading to a blocked flue or a chimney fire.

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.

Deliberately or Accidentally Sealed-off Chimney Tops & Flues

Two problem chimney top terminations (C) Daniel Friedman

As we illustrate in our photo at above 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.

Watch out: for flat stones, slate, or other covers that may have been placed atop a chimney that was thought to be out of use (photo, above left [Click to enlarge any image]). We've encountered cases of a homeowner returning to service a fireplace or chimney flue whose top was covered over completely as our photo depicts. The result is potentially fatal carbon monoxide poisoning or a fireplace that causes smoke damage in the building.

Also see MASONRY CHIMNEY TOP DAMAGE.

Photograph of a damaged masonry chimney. Chimney top blocked by flat stone or slate (C) Daniel Friedman

Above we illustrate more r "sealed-off" masonry chimneys.

At above-left, 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

At above-right someone has placed solid slate atop a presumably-un-used brick chimney.

Lost or Missing Chimney Rain Cap

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.

Missing rain cap on factory built metal chimney, New Hampshire (C) Daniel Friedman Lost rain cap on metal chimney (C) Daniel Friedman Water entering a chimney from a missing rain cap (C) Daniel Friedman

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. At above right we see leak stains from water that has been running down the interior of this heating appliance chimney flue.

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.

Corroded metal chimney cap risks loss of the cap and later flue or heater damage (C) Daniel Friedman Corroded metal chimney cap risks loss of the cap and later flue or heater damage (C) Daniel Friedman

The stainless steel chimney cap shown in the two photos above sports a more subtle hazard. Corrosion at the welds that connect the round chimney cap to the metal brackets that in turn connect the chimney cap to its mounting base has caused the welds to fail. Only one of 10 welds remained in place when I inspected this chimney; one good gust of wind was sufficient to blow the cap off of this flue, risking subsequent water damage to the chimney itself or to the oil fired heating boiler connected to this chimney.

Particularly because this chimney was installed through a flat roof and was not close to the roof edge, you'd not find this hazard without an on-roof direct inspection.

Damaged or Defective Metal Rain Caps on Chimneys

Leaks at a home made chimney rain cap and at a bent, damaged factory-built chimney rain cap

Hole in home-made metal rain cap on a brick chimney (C) Daniel Friedman Damaged metal chimney rain cap (C) Daniel Friedman

The home made metal chimney cover on a brick flue (above left) has rusted through risking water damage to the chimney, flue liner, or to appliances being vented through this flue.

[Click to enlarge any image]

The concave stailess steel metal chimney rain cap shown at above right 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.

Damaged / Defective Masonry, Stone, Slate Chimney Rain Caps

Brooklyn chimney collapse (C) Daniel Friedman

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 REPAIRS, TOP & CLAY FLUE TILE.

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.

Rust damaged chimney cap & rain cap (C) Daniel Friedman

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.

Rusted out metal chimney and cap (C) Daniel Friedman

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.

Rust Damaged Chimney Turbine Vent or Turbulator Vent Cap

Rusty turbulator cap or turbine cap set atop a masonry chimney (C) Daniel Friedman

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.

Squashed or Non-Listed Chimney Rain Cap Hazards: inadequate exhaust openings are unsafe

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.

Rusty turbulator cap or turbine cap set atop a masonry chimney (C) Daniel Friedman Squashed unsafe chimney rain cap (C) InspectAPedia TW

We suspect that this little rain cap at above left 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.

At above right the round metal chimney rain cover seems to be so squashed-down as to nearly block the venting of that flue, perhaps explaining the stains and heat-damaged sealant around the flue (red and yellow arrows).

See CHIMNEY RAIN CAP OPENING SIZE

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

Or see CHIMNEY INSPECTION at ROOFTOP

Or see CHIMNEY INSPECTION DIAGNOSIS REPAIR - home

Or see these

Chimney Top Cap, Crown, Rain Cap Article Series Contents

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INDEX to RELATED ARTICLES: ARTICLE INDEX to CHIMNEYS & FLUES

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