CHIMNEY CRACK DETECTION & DIAGNOSIS - CONTENTS: 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
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Diagnose cracks in chimneys:
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.
This article series on chimneys, chimney construction, 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.
Guide to Diagnosing & Evaluating Cracks in Brick Chimneys
Our brick chimney photographs just above illustrate a common (and dangerous) crack pattern found in corbeled (stair-stepped) chimneys where a brick chimney passes through an attic floor and is angled over to exit at the chimney ridge.
At the chimney in our photo at above left, look very closely at the masonry joint where the chimney begins its transition from vertical to angled.
To prevent cracks in a leaned-brick chimney such as this one, the chimney depends on absolutely stable support by the roof framing structure where it passes through the roof to outside. Unless the brick chimney was adequately supported and constructed it may lean, causing the crack pattern we show at above right.
Watch out: often the crack in a leaning brick chimney occurs at the attic floor where the chimney begins its transition from vertical to angled - a spot where the crack may be hard to spot.
See CHIMNEY INSPECTION INDOORS for a discussion of chimney movement that opens a hard-to-find crack where a corbeled brick chimney passes through an attic floor.
List of Typical Causes of Cracks in Brick Masonry Chimneys & Flues
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 rain cap, faulty chimney cap 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.
We illustrate water and frost damage to a brick chimney in this article, below.
Chimney movement: a chimney which is set on a defective footing or foundation (more improper chimney construction) or a chimney which was not properly secured to the building may lean, bend, or curl, leading to cracks that usually appear in the mortar joints.
See BRACING for MASONRY CHIMNEYS
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. We illustrate thermal cracking in a brick chimney in this article, just below.
Mechanical damaged chimney cracking: a masonry chimney may crack due to stresses from a chimney-mounted antenna, or from earthquake or nearby site blasting stresses.
See EARTHQUAKE CHIMNEY COLLAPSE DANGERS
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.
Frost Cracking in Brick Chimneys & Flues - outdoor & indoor evidence of brick chimney damage
At left we show a very common crack pattern found in brick masonry chimneys & flues - water and frost cracking at the chimney top.
Considering that there is a nice thick concrete chimney cap. why do we have this brick movement and mortar-joint cracking?
Perhaps the chimney cap is cracked, flat, not draining, or it was not sealed around the flue, or a rain cap was missing.
At below left we show a very common crack pattern found in brick masonry chimneys & flues - a collection of vertical, diagonal, and even some horizontal chimney cracks that are probably due to a combination of water intrusion and (in freezing climates) frost cracking.
Even if you do not immediately notice the chimney cracks themselves you are likely to spot this chimney damage by the creosote stains carried to the chimney surface by water entry into the chimney flue.
Of course had these cracks and stains been present on a hidden side of the chimney, say between the chimney and a close-by gable-end wall, you'd not see these clues from within the attic.
But inspecting this chimney outside, if it has had no proper rain cap and chimney cap you should be extra alert for water and frost damage to the chimney and its flue.
A second set of clues - water leak stains, may be visible in a fireplace or at a chimney cleanout lower in the building.
Thermal Cracking in Brick Chimneys & Flues May Produce Thin Vertical Openings
At left we show a very common crack pattern found in brick masonry chimneys & flues - a vertical crack that begins in a mortar joint and extends through individual bricks themselves.
Cracked chimney masonry such as shown in the photo of cracks in a brick chimney exterior (at left), may
a safety concern if the flue liner or chimney are not intact and fire/gas safe.
The brick chimney crack type shown here is more often caused by thermal expansion (and improper chimney construction) than by frost - frost cracking is often more visually obvious and is often accompanied by brick spalling.
Severe Chimney Cracking - Deteriorated, Collapsing Brick or Masonry Block Chimneys
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.
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.
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(Sept 22, 2011) Fishin said:
How do you repair this? Mine is just like the picture as it goes through the mortar and the brick. It originated from the air vent, I assume because the metal air vent got hot. Thanks.
If a chimney has minor cracks but is structurally sound it may be repaired by re-lining. If the chimney is in danger of collapse it should be removed and replaced. You need an on-site expert to make such a determination. Don't forget to have the flue interior inspected for safety before using such a chimney at all.
Question: smoke coming out of cracks
(Sept 26, 2012) david said:
i have installed about 20 woodburners, and always have them signed off by hetas engineer.... At my own house i have recently fitted wood burner about 5kw, stainless 316/316 flue, pot, ufo cowel. next door is getting smoke done her living room chinmey which has all pot capped on room with pepper posts.
I taped the pepper pots up with gaffa and smoke bombed the fire next door up the flue - it came out of cracks in mortor and around pepper pots still. could it pull down through these cracks and fill the living room next door??? (raised pot from standard to 600mm high laready to try aid the problem.
Watch out: you are describing both a house fire hazard and a chimney operation and draft problem. It's time for a professional chimney sweep's inspection.
Question: gaps at the fireplace sides
(Nov 16, 2014) Jeannie D said:
Last night as my husband built the first wood fire of the season in our fireplace, I noticed a gap between the fire bricks lining the inside of the fire box. The opening was between the bricks on the right side of the fire box and the back of the fire box. When the fire died down, I used the metal fire poker and found I could insert the poker through the gap in the bricks to the metal fire box liner. Is this dangerous? Should I arrange for a fireplace and chimney inspection? My husband doesn't think it's a problem. Thank you.
Watch out: the opening you describe could be a serious fire hazard. It may also introduce draft problems that interfere with chimney operation.
Question: ok to use a cracked chimney pot?
(Nov 30, 2014) Clair said:
I have just re-opened my fireplace to make an open fire. I have a chimney pot to put on but it has a vertical crack in the side ... can this still be used in its current state? if not can it be repaired?
(Nov 30, 2014) (mod) said:
Clair I'd replace the cracked chimney pot rather than trying a repair. You might be able to fill the crack with cement or even an epoxy, but exposed to the weather I'd not expect it to last.
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Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com
John Cranor is an ASHI member and a home inspector (The House Whisperer) is located in Glen Allen, VA 23060. He is also a contributor to InspectApedia.com in several technical areas such as plumbing and appliances (dryer vents). Contact Mr. Cranor at 804-747-7747 or by Email: firstname.lastname@example.org
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 email@example.com
Roger Hankeyis 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 #211-3.1 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.
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_Repair.php. 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
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 - 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
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: firstname.lastname@example.org. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides extensive home inspection education and report writing material.
The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors. Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones