Cracks and spits in brick chimney sides - what is their cause, significance, danger?
How to diagnose the cause of cracks in brick, concrete block and stone chimneys
How to evaluate the importance of cracks in masonry chimneys
Questions & answers about how to diagnose & repair chimney cracks
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This article catalogs the types of chimney cracks and movement that may be found in brick, stone, or concrete block chimneys; we describe the inspection and and diagnosis of the cause of each type of chimney cracking and we suggest the probable severity, safety concerns, and chimney repairs that may be necessary. We include links to additional detailed articles about each type of chimney cracking or movement.
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.
As with most inspection and safety topics, this material may be incomplete.
Guide to Diagnosing & Evaluating Thin Cracks in Brick Chimneys
Cracked chimney masonry such as shown in this photo of cracks in a brick chimney exterior, may
a safety concern if the flue liner or chimney are not intact and fire/gas safe.
Cracks in a brick masonry chimney such as shown in these photographs may be caused by improper original chimney construction. This damage also appears on concrete block constructed chimneys.
Improper construction: failure to leave air space between flue line and masonry chimney sides - if the mason does not leave an expansion
gap surrounding the clay flue liners as they are set into the chimney during construction, as the flue heats up during use, the expanding flue may crack the surrounding brick.
Water leaks: at the chimney top (missing cap, faulty top seal), or at the chimney sides (defective flashing, wind-blown rain, open mortar joints) can send water into the chimney structure where in freezing climates frost can lead to cracks to the chimney itself or to its flue liner.
Chimney movement: a chimney which is set on a defective footing or foundation or which was not properly secured to the building may lean, bend, or curl, leading to cracks that usually appear in the mortar joints. see Chimney Inspection Indoor Procedures for a discussion of chimney movement that opens a hard-to-find crack where a corbelled brick chimney passes through an attic floor.
Thermal expansion cracks in chimneys: a masonry chimney may crack from thermal expansion, or its internal flue may crack from thermal expansion, if the chimney was not properly constructed, failing to leave space for movement as the chimney interior heats up when in use. See THERMAL EXPANSION of MATERIALS for a table of the coefficient of expansion of common building materials.
The second cracked chimney at above right is a bit more suspect because we see what might be traces of
soot or creosote having washed out through the cracks to the chimney exterior. If this proves to be
the case this flue is certainly seriously damaged.
Severe Chimney Cracking - Deteriorated, Collapsing Brick or Masonry Block Chimneys
WARNING: Cracks in a chimney can be very significant and dangerous, risking fire or chimney collapse. Be sure to review the articles at CHIMNEY CRACK & COLLAPSE HAZARDS.
Cracks in Masonry Block or Concrete Block Chimneys
Cracks in a masonry chimney, particularly concrete block chimneys are often caused by
chimney footing tipping or settlement (inadequate foundation)\
frost (poor drainage, missing rain cap, porous masonry, improper construction in freezing climates)
thermal expansion of the clay flue liner (improper construction)
Chimney Cracks due to Chimney Movement, Tipping, Leaning
Chimneys that lean, curve, bulge, tip, or otherwise move due to footing settlement and tipping or due to failure to secure a tall chimney to the building also may produce both visible cracks on the chimney exterior and hidden cracks and damage to the chimney flue.
The risk of an unsafe chimney flue lies behind our advice that a thorough inspection of the entire chimney flue is necessary when there is any evidence of chimney movement.
see Chimney Leaning, Separation, Movement-Outdoors for details of the detection, analysis, and repair of leaning and tipping chimneys and chimneys that have separated from their building.
Curved Brick Masonry Chimneys
Especially on older buildings using brick chimneys, and more so where the chimney flue is not lined with a modern clay liner, brick chimneys may be seen to curve in one direction.
Often all of the similar chimneys in a neighborhood curve in the same direction. It's not a coincidence. A brick chimney will often curve away from its most weather-exposed side due to sulphation - expanding brick mortar joints caused by the combination of water and sulphur or other minerals.
see Curved Brick Chimneys for further explanation of the cause, significance, and cure of curved brick chimneys.
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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
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
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
Ceramic Roofware, Hans Van Lemmen, Shire Library, 2008, ISBN-13: 978-0747805694 - Brick chimneys, chimney-pots and roof and ridge tiles have been a feature of the roofs of a wide range of buildings since the late Middle Ages. In the first instance this ceramic roofware was functional - to make the roof weatherproof and to provide an outlet for smoke - but it could also be very decorative.
The practical and ornamental aspects of ceramic roofware can still be seen throughout Britain, particularly on buildings of the Victorian and Edwardian periods. Not only do these often have ornate chimneys and roof tiles but they may also feature ornamental sculptures or highly decorative gable ends. This book charts the history of ceramic roofware from the Middle Ages to the present day, highlighting both practical and decorative applications, and giving information about manufacturers and on the styles and techniques of production and decoration.
Hans van Lemmen is an established author on the history of tiles and has lectured on the subject in Britain and elsewhere. He is founder member and presently publications editor of the British Tiles and Architectural Ceramics Society. Also available at the InspectAPedia Bookstore.
Chimney & Stack Inspection Guidelines, American Society of Civil Engineers, 2003 - These guidelines address the inspection of chimneys and stacks. Each guideline assists owners in determining what level of inspection is appropriate to a particular chimney and provides common criteria so that all parties involved have a clear understanding of the scope of the inspection and the end product required. Each chimney or stack is a unique structure, subject to both aggressive operating and natural environments, and degradation over time. Such degradation may be managed via a prudent inspection program followed by maintenance work on any equipment or structure determined to be in need of attention. Sample inspection report specifications, sample field inspection data forms, and an example of a developed plan of a concrete chimney are included in the guidelines. This book provides a valuable guidance tool for chimney and stack inspections and also offers a set of references for these particular inspections.
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 - 3-4 - 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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