Chimney & Flue Inspection, at the Rooftop InspectAPedia® -
Chimney inspection procedures on the rooftop: rooftop chimney defects
Detailed Inspection & Photo Guide to chimney defects
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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.
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. 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 Outdoors From Ground. Readers should also see Chimney Crack & Collapse Risks, Repairs.
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.
Suggestions for Inspecting Chimney Caps & Crowns
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" and "chimney crown":
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".
Some people call this the 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.
The 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.
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: 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.
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.
The concrete crown in our photo (above) 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 sketche (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 or Crown
Chimney Cap: 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.
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Additional technical contributors & reference sources for this article are listed below.
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Thanks to Luke Barnes for suggesting that we add text regarding the hazards of shared chimney flues. USMA - Sept. 2008.
Arlene Puentes, an ASHI member and a licensed home inspector in Kingston, NY, and has served on ASHI national committees as well as HVASHI Chapter President. Ms. Puentes can be contacted at ap@octoberhome.com
Roger Hankey is principal of Hankey and Brown home inspectors, Eden Prairie, MN, technical review by Roger Hankey, prior chairman, Standards Committee, American Society of Home Inspectors - ASHI. 952 829-0044 - hankeyandbrown.com
Residential Masonry Fireplace and Chimney Handbook, James E. Amrhein, S.E., MIA, Masonry Institute of America, 2d. Ed., 1995, ISBN 0-940116-29-4. The MIA is in Los Angeles, CA 213-388-0472. This manual reflects the 1994 Uniform Building Code, Energy Conservation Requirements of California, and the U.S. Department of Housing and Urban Development - HUD. The complete UBC is available from the International Conference of Building Officials (ICBO), Whittier CA 310-699-0541.
NFPA 211 - Standards for Chimneys & Fireplaces, NFPA 211: Standard for Chimneys, Fireplaces, Vents, and Solid Fuel-Burning Appliances, 2006 Edition (older editions and standards are found at the same bookstore)
NFPA #211-3.1 1988 -
Specific to chimneys, fireplaces, vents and solid fuel burning appliances.
NFPA # 54-7.1 1992 -
Specific to venting of equipment with fan-assisted combustion systems.
GAMA -
Gas Appliance Manufacturers' Association has prepared venting tables for
Category I draft hood equipped central furnaces as well as fan-assisted
combustion system central furnaces.
National Fuel Gas Code, an American National Standard, 4th ed. 1988 (newer edition is available) Secretariats, American Gas Association (AGA), 1515 Wilson Blvd., Arlington VA22209, and National Fire Protection Association (NFPA), Batterymarch Park, Quincy MA 02269. ANSI Z223.1-1988 - NFPA 54-1988. WARNING: be sure to check clearances and other safety guidelines in the latest edition of these standards.
Fire Inspector Guidebook, A Correlation of Fire Safety Requirements Contained in the 1987 BOCA National Codes, (newer edition available), Building Officials and Code Administrators International, Inc. (BOCA), Country Club HIlls, IL 60478 312-799-2300 4th ed. Note: this document is reissued every four years. Be sure to obtain the latest edition.
Uniform Mechanical Code - UMC 1991, Sec 913 (a.) Masonry Chimneys,
refers to Chapters 23, 29, and 37 of the Building Code.
New York 1984 Uniform Fire
Prevention and Building Code, Article 10, Heating, Ventilating, and Air Conditioning Requirements
New York 1979 Uniform Fire Prevention & Building Code, The "requirement" for 8" of solid masonry OR for use of a
flue liner was listed in the One and Two Family Dwelling Code for New
York, in 1979, in Chapter 9, Chimneys and Fireplaces, New York 1979
Building and Fire Prevention Code:
"Top Ten Chimney (and related) Problems Encountered by One Chimney Sweep," Hudson Valley ASHI education seminar, 3 January 2000, contributed by Bob Hansen, ASHI
"Rooftop View Turns to Darkness," Martine Costello, Josh Kovner, New Haven Register, 12 May 1992 p. 11: Catherine Murphy was sunning on a building roof when a chimney collapsed; she fell into and was trapped inside the chimney until rescued by emergency workers.
"Chimneys and Vents," Mark J. Reinmiller, P.E., ASHI Technical Journal, Vol. 1 No. 2 July 1991 p. 34-38.
"Chimney Inspection Procedures & Codes," Donald V. Cohen was to be published in the first volume of the 1994 ASHI Technical Journal by D. Friedman, then editor/publisher of that publication. The production of the ASHI Technical Journal and future editions was cancelled by ASHI President Patrick Porzio. Some of the content of Mr. Cohen's original submission has been included in this more complete chimney inspection article: InspectAPedia.com/chimneys/Chimney_Inspection.htm. Copies of earlier editions of the ASHI Technical Journal are available from ASHI, the American Society of Home Inspectors.
Natural Gas Weekly Update: http://tonto.eia.doe.gov/oog/info/ngw/ngupdate.asp Official Energy Statistics from the U.S. Government
US Energy Administration: Electrical Energy Costs http://www.eia.doe.gov/fuelelectric.html
Critique, contributions wanted: Contact Us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.
More Information on Building Diagnostic Inspections and Repairs
NFPA 211 - 3-1.10 - Relining guide for chimneys
NFPA 211 - 3-2 - Construction of Masonry Chimneys
NFPA 211 - 3-3 - Termination Height for chimneys
NFPA 211 - 3-4 - Clearance from Combustible Material
NFPA 54 - 7-1 - Venting of Equipment into chimneys
Brick Institute of America - Flashing Chimneys
Brick Institute of America - Proper Chimney Crowns
Brick Institute of America - Moisture Resistance of Brick
American Gas Association - New Vent Sizing Tables
Chimney Safety Institute of America - Chimney Fires: Causes, Effects, Evaluation
National Chimney Sweep Guild - Yellow Pages of Suppliers
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