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This article describes chimney top repairs for masonry chimneys and clay flue tiles, work performed at or from the rooftop. 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.
Repair of Damaged Clay Chimney Flue Liners at the Rooftop
Determine the Extent of Chimney Damage and the Safety of the Entire Chimney Flue
Our photo above shows an unsafe chimney that was still in active use. Notice those missing bricks and lost mortar? Damaged chimney top masonry such as missing bricks and a missing chimney cap were easily spotted from ground level, raising a critical concern for the fire and gas-leak safety of the clay flue tiles lining this chimney.
[Click to enlarge any image]
At the front left corner of the clay chimney flue tile you can see our pen inserted into an opening between the chimney flue tile and the (damaged) surrounding brick and concrete chimney structure - water entering the chimney structure at this location risks freeze damage to the chimney flue itself, resulting in potentially very dangerous conditions.
First, you will want to be absolutely sure that the chimney damage, whether to the ceramic clay flue liner or to the surrounding masonry or both, is limited to the upper, visible, accessible part of the chimney. Our chimney clay flue tile liner damage photos above show enough wear and cracking (above left) and opening between clay flue tile liner sections (above right) that further inspection and repair by a chimney professional is warranted.
Other chimney damage lower in the chimney itself as it passes through or alongside the building could be very dangerous, even fatal if carbon monoxide or other flue gases leak into the building or if sparks cause a fire.
Our photos above show damage to the chimney clay flue tiles near the chimney top, with multiple cracks in the clay flue liner (above left), and severe spalling in the clay flue tile liner (above right) -these are two different chimneys. Both need repair. The right hand chimney (above right) may need a complete re-lining while the chimney at above left might be damaged only above the roof line, making roof top repair a reasonable approach.
We suggest that you hire a professional chimney sweep who can examine the entire chimney flue. Most chimney sweeps also offer repair services, and can suggest what repairs are needed and give alternatives for the particular chimney and flue on your building.
Reline the Chimney versus Repairs Just at the Chimney Top
Our photo of spalling brick near the top of this masonry chimney (left) shows damage almost certainly caused by frost. Without a view of the chimney top, however, we don't know exactly where water was leaking into the structure, nor the condition of the flue liner itself. It is the condition of the fire clay (or as some call it "ceramic") flue liner that is of course critical to safe venting of flue gases outside.
Some chimney repair contractors will want to reline the whole chimney flue - an approach that is often safe, quick, easy, and profitable. But this approach may be inappropriate if the damage is just due to weather at the chimney top and the rest of the flue is intact and safe.
Water leaking between the flue liner and the masonry surround is also a very common cause of water and frost damage at the chimney top.
Most often we see spalling flue liners and loose or damaged bricks or concrete block around a chimney top caused in large part by failure to protect the chimney to from the weather; lack of an allowance for thermal movement among chimney parts, especially the liner and the surrounding masonry,can also crack and break the flue liner, especially on the above-roof portion where the chimney is in northern climates exposed to coldest temperatures. Potentially, damage to the masonry chimney structure as well as to its clay flue tile liner can occur also inside a freezing attic space.
If the damage is just at the top of the chimney and its masonry flue liner, repairs can usually be completed entirely from outside, working from the rooftop. (Be sure the mason performing the repairs protects the surrounding roof surface from damage lest your chimney repair be followed by roof leaks.)
Other Chimney Top Repairs for Damaged Flue Liners or Surrounding Masonry
Some people try patching the damaged areas of the chimney top or chimney flue with refractory cement but we don't recommend applying "patches" to the interior of a chimney flue: there is a risk that the "patch" might later fall into and block the flue - a very dangerous condition.
A better approach and the one used by most chimney repair masons who are not going to simply reline the flue, is to remove all of the damaged materials down to sound chimney flue liner and brick or block, then rebuild with new clay flue liner and brick (or block), adding an appropriate chimney cap and top seal.
Using solid masonry between the clay liner and the surrounding masonry at the chimney top is a common practice (photo at left), and having inspected quite a few chimney tops, we can't say that every chimney built this way fails, but it is not the best practice and is not recommended by experts.
Our chimney top photo (at above left) shows that this roof top chimney seal is already cracking, threatening future damage to the chimney flue liner as well as the chimney structure at roof top.
Other problems at this chimney top include the termination of both flues at the same height, and the absence of any rain cap.
Using a fire-safe flexible caulk at that joint will reduce the chances of cracking due to temperature differences.
Carson Dunlop's sketch ( above-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.
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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.
"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
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.
Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.
Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment 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.
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 & 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 #211-3.1 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:
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