Photograph of a damaged masonry chimney. Chimney & Flue Inspection, at the Rooftop

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This article describes chimney defects that can best be spotted and diagnosed by on-roof access. These include inspection of the chimney cap and crown or top seal, the condition of the uppermost chimney flue, the separation of multiple chimney flues. Additional rooftop chimney inspection details are provided in subsequent sections of this article. These articles on chimneys and chimney safety provide detailed suggestions describing how to perform a thorough visual inspection of chimneys for safety and other defects. Chimney inspection methods and chimney repair methods are also discussed.

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Rooftop Chimney Inspection at the Rooftop

Improper chimney flue construction risks hidden damage (C) Daniel FriedmanWatch out: Climbing ladders and accessing roofs is inherently dangerous and was the cause of the first home inspector death recorded to have occurred during a home inspection.

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Home inspectors are not required to climb onto a roof which for any reason the inspector feels is unsafe or too fragile for direct access.

However this article describes describes chimney defects which may be difficult or impossible to detect from a ground-level inspection. If you have not done so, see CHIMNEY INSPECTION from GROUND CHIMNEY COLLAPSE RISKS, REPAIRS.

Watch out: at the same time, there are many rooftop defects, including potentially costly or dangerous problems, that cannot be discovered by a from-ground-level inspection, even using high powered binoculars. At left is an example: an improperly-constructed chimney flue and cap that risk leaks and hidden damage to the chimney flue. More examples of chimney flue damage are at Flue Tile Damage in Chimneys.

An on-roof inspection of the chimney allows inspecting the upper portion of the flue lining, cap and roof flashing, chimney top seal or "crown", and it permits a closer inspection of masonry chimneys for cracking or other damage that might not be visible from a more remote "from ground" inspection.

Summary of Inspection Points at Chimney Caps & Crowns

Chimney cap (C) Daniel FriedmanSee CHIMNEY CAP & CROWN for details about chimney caps & crowns where we detail the various types of covers & terminations found at the top of chimneys and flues & their common defects. There we also cite pertinent chimney top cap / crown building codes & standards.

Rain Cap: 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. The metal cover shown in our photo at left is a metal "rain cap".

This interesting chimney has a metal cap on one flue and not the other. The metal chimney cap looks home-made and perhaps not functional.

Chimney Cap: 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 (above left) the chimney cap, also called a mortar cap, is the white concrete visible around the projecting flue tiles at the top of the chimney. Some of us call the mortar cap or concrete chimney cap the chimney crown. The Masonry Institute of America calls this the "chimney cap" - we're following their terminology.

Chimney cap and spark arrestor (C) Carson Dunlop AssociatesThe purpose of the chimney cap [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 rain rain cap has the job of keeping rain and wind down-drafts out of the chimney. The rain cap or hood may also be charged with preventing sparks from leaving the chimney - a fire safety measure shown in Carson Dunlop's Sketch.

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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.

Chimney cap slope (C) Carson Dunlop AssociatesChimney 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.

Lost rain cap (C) Carson Dunlop Associates

Missing Chimney Rain Cap

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 Carson Dunlop's sketch shows, a missing cap invites water damage to the chimney and the equipment it vents, draft problems, and unsafe operation.

Water entering the chimney can cause enough corrosion in a metal flue that the chimney needs replacement.

Chimney top missing drop edge (C) Carson Dunlop Associates

Chimney crown/cap damage or missing drip edge

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.

Chimney top cap construction details (C) Carson Dunlop Associates

Carson Dunlop's sketch (left) shows some details of good chimney crown/cap construction. The object of these details is to avoid water and frost damage to the flue or to the chimney itself.

Chimney crown/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 or Crown

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

Chimney Cap/crown: 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 but no rain cap. 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.

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.

See CHIMNEY CAP & CROWN for definitions of chimney rain cap, chimney cap, chimney crown, and for more examples of chimney top defects that may be visible from the ground or from an on-roof inspection.

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