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Cracked Concrete Block Chimneys: Diagnosis & Repair Guide InspectAPedia®  -     Detailed Inspection & Photo Guide to diagnosing and acting on cracks in a concrete block chimney Chimney safety & repair advice

This article describes cracks in masonry block or concrete block chimneys and suggests possible causes and crack severity.

Cracks in a masonry chimney, particularly concrete block (this article) and perhaps brick may be 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)
• mechanical damage,
• or perhaps other events

Readers should also see Chimney Inspection Outdoors From Ground where we discuss other significant Chimney Cracks, Separation, Movement.

This website provides 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. © Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

Cracked Concrete Block Chimneys

Both outdoors and indoors we may also see chimney cracks which could be due to chimney movement (introduced above) or due to compression loads or other chimney construction problems (photograph below).

Cracks in a masonry block chimney always deserve further investigation to identify the probable cause, to decide on the remedy and to evaluate the safety and function of the chimney.

We recommend that you have any cracked or damaged chimney thoroughly inspected by a professional, including an inspection of the integrity of the chimney flue and of any fireplaces or other attached heating systems.

Cracked concrete block chimneys: Our photo at left shows dangerous cracking indoors in a concrete block chimney used to vent a heating appliance. You might also notice that the barometric damper is not level - a much simpler problem to correct. As a chimney leans away from the house we might find several serious problems caused by that movement: Damaged, unsafe chimney liner (flue gas leaks or sparks into the building interior, a fire or potentially fatal carbon monoxide hazard) Damaged, unsafe fireplaces where the chimney has pulled the firebox away from the building or created dangerous openings around the fireplace into the building structure, risking both sparks (and fire) or air leaks (and inability to control the draft). Leaks into the building walls (flue gas leaks or sparks into the building interior, a fire or potentially fatal carbon monoxide hazard) Unsafe fireplaces in the building: hearth cracks, fireplace side cracks, chimney damage all present risks of sparks or smoke entering the building cavities, a fire and flue gas risk. Check for evidence of movement at the fireplace. (Flue gas leaks or sparks into the building interior, a fire or potentially fatal carbon monoxide hazard) Also see Chimney Crack Detection & Diagnosis If you see repairs such as shown in the our photo (left) the chimney should be professionally inspected, especially to establish the condition of the flue liner as it may be unsafe. Our pen points to a gap between masonry block chimney and a building wall, indicating chimney movement and raising question about other less obvious crack and damage to this structure. It may be possible to repair minor chimney racks with masonry products provided that the underlying cause is also identified and corrected. Also, some concrete blocks may be cracked during their individual drying/curing process, a condition not to be confused with chimney cracking. The usual repair when a significant chimney crack has occurred, damaging the chimney and the flue is to remove and replace the chimney, though in some cases it may be possible to re-line the chimney and to jack an intact masonry chimney back to level and repair its connections into the building.

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Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

CHIMNEY INSPECTION DIAGNOSIS REPAIR
CHIMNEY INSPECTION & REPAIR GUIDE
CHIMNEY INSPECTION DIAGNOSIS REPAIR
Chimneys Cleaning Advice, Procedures
Chimney Cleanout Doors
Chimney Crack & Collapse Risks, Repairs
  Articles on Collapsing Chimneys
    Bracing for Masonry Chimneys
    Bracing for Masonry Chimneys, Lateral
    Bracing for Metal Chimneys
  Bracket Chimney Collapse & Fire Risks
  Chimney Movement - Outdoor Evidence
    Separation from Building
    Settlement, Leaning
    Foundation Support for Masonry Chimneys
  Chimney Movement - Causes
  Chimney Movement - Indoor Evidence
  Chimney Movement - Ongoing vs Static
  Chimney Crack Detection & Diagnosis
  Cracked Concrete Block Chimneys
  Curved Brick Chimneys
  Earthquake Chimney Collapse Dangers
  Leaning Chimney Repair Methods
  Split Openings in Brick & Chimney Collapse
Chimney Draft & Performance
Chimney Inspection Checklist
Chimney Inspection Indoor Procedures
Attic Chimney Inspection
Chimney Inspection Outdoors From Ground
Chimney Crack Detection & Diagnosis
Chimney Inspection Outdoors From Ground
Chimney Height & Clearance
Chimney Inspection Outdoors at Rooftop
Chimney Cap & Crown Inspection
Chimney Types & Materials
Chimney Cleanout Doors
Fire Clearances for Masonry Chimneys
Fire Clearances for Metal Chimneys
Fire Clearances, Single-Wall Metal Flues
Flue Sizing of Chimneys
Fire Stopping Between Floors
Flue Vent Connectors - Boilers, Furnaces
Chimney Inspection: Flue Interiors
Metal Chimneys & Flues
Shared Chimney & Shared Flue Hazards
Fireplace Damage & Unsafe Hearths - Settlement
Moisture Problems Damage Chimneys
Wood Burning Heaters Fireplaces Stoves

• Thanks to Alan Carson and Bob Dunlop, Carson Dunlop, Associates, Toronto, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education, publications, report writing materials, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
• 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
• Chimney Building Codes and Chimney, Flue, and Appliance Venting Standards
  • 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
• Chimney Inspection Checklist, Carson Dunlop, Associates, Toronto, Ontario
• "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 Chimney Inspection, Testing, Diagnosis, & Repair

• Books, Complete List of Fireplace & Chimney Design, Inspection, Repair Books at the InspectAPedia Bookstore.
• 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. Available at the InspectAPedia Bookstore.
• Chimney Inspection Checklist, Carson Dunlop, Associates, Toronto, Ontario
• 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.
• Fireplaces, a Practical Design Guide, Jane Gitlin
• Fireplaces, Friend or Foe, Robert D. Mayo
• NFPA 211 - Standards for Chimneys & Fireplaces, NFPA
• Principles of Home Inspection: Chimneys & Wood Heating (Principles of Home Inspection), Carson Dunlop
• Woodstove & Fireplace Maintenance & Safety, L. L. Helwig

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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