Height & Clearance Requirements for Chimneys InspectAPedia® -
Height requirements for chimneys - rooftop chimney distances & clearances
Masonry chimney top clearances at rooftop - chimneys that are too short
Fireplace chimney rooftop clearance requirements
Metal chimney rooftop clearance requirements; B-vent rooftop clearances.
Separation requirements between multiple adjacent chimneys on a building.
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This article describes the height requirements for chimneys, including rooftop clearances and overall chimney height necessary for proper chimney draft and function and for fire safety. Readers should also see Chimney Height Extensions.
A variation on a "too short" metal or masonry chimney is a chimney that may look tall-enough to some folks but which lacks adequate clearance from a nearby roof slope.
Chimney to Roof Clearance: from the ground you can guess and from on-roof
access you can measure to determine if a chimney is simply too short for fire safety
and code compliance.
The top of the flue should be two feet above the height of a
horizontal line drawn from the chimney to the point at which that line touches
the roof surface ten feet away.
In our photo, the tap is pulled to about four and a half feet. This line needs to be ten feet.
Or if the chimney is closer to or right at the peak or ridge of the roof, the chimney should extend at least two feet above the ridge.
This photo is slightly incorrect (I didn't want to lose my tape down the flue while taking the picture).
Measure from the edge of the chimney flue closest to the roof, horizontally, until you
touch the roof surface to get this clearance distance.
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.
Chimneys Too Short
A chimney that is too short is unlikely to vent properly and it may also be a serious fire hazard to the building, risking setting the roof on fire. The photo at above left is a too-short masonry chimney (with no cap and other worries).
The photo at above right is a too-short metal chimney that is less than two feet above the ridge. We also notice that the chimney cap is discolored on this metal flue - possibly indicating an overheated appliance or other unsafe condition. Did you also notice that the sides of the chimney flashing are on top of rather than under the roof shingles?
Just how short is "too short" - we discuss chimney height and roof clearance requirements beginning at Chimney Height Above Roof - the next section of this article.
We discuss examples of extending chimney height to improve draft, performance, and fire safety at Chimney Height Extensions.
Required Chimney Height Above Roof Surfaces or Ridges
Masonry Chimney Roof Clearance Requirements
The sketch at left shows the proper minimum chimney height and roof clearances for a masonry chimney.
Masonry chimneys must terminate at least 3 feet above the highest point
of contact with the roof structure (left-most measurement as in our sketch at left), and chimneys should extend 2 feet higher than any part of the structure within 10 feet horizontally (measurements as shown on the right side of the chimney in our sketch).
Carson Dunlop's sketch at left shows that the minimum chimney height above a wood burning fireplace is 15', and that a shorter minimum of 5' may be acceptable above the draft hood of a gas furnace is allowed in some jurisdictions.
Adjacent Metal Chimney Separation Requirements
In addition to the requirement for safety fire clearance from rooftops and other building components, separate metal chimneys that are too close to one another may cause damage resulting in poor chimney performance or an unsafe chimney.
Carson Dunlop's sketch at left shows that metal chimneys should be at least 16" (that's 16 inches) apart to avoid damage.
Table of Type B-Vent Rooftop Clearance Requirements
The 1992 Vent Sizing Tables require that all Type B gas vents terminate
above the roof with a listed cap or listed roof assembly in accordance with the
manufacturer's instructions.
Vent caps 12" and smaller may terminate a distance
above the roof if 8 feet or more away from a vertical surface as follows:
ROOF PITCH - rise/run in inches
MINIMUM HEIGHT*
Flat to 7/12 - 1.0 foot above the roof surface
7/12 to 8/12 - 1.5 feet above the roof surface
8/12 to 9/12 - 2.0 feet above the roof surface
9/12 to 10/12 - 2.5 feet above the roof surface
10/12 to 11/12 - 3.25 feet above the roof surface
11/12 to 12/12 - 4.0 feet above the roof surface
* Continues to 21/12 pitch at 8.0 feet
Vent caps larger than 12" must be located at least 2 feet above the
highest point and 2 feet higher than any portion of the building within a horizontal
distance of 10 feet.
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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
G. Howard suggested text clarification on proper chimney height and roof clearances, August 2009.
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 Chimney 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. 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)
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
InspectAPedia® Home & Site Map - Building & Environmental Inspection, Testing, Diagnosis, Repair, & Problem Prevention Advice: In-depth research & advice on diagnosing, testing, correcting, & preventing building defects & indoor environmental hazards. Unbiased information, no conflicts of interest.
The Mold Information Center: What to Do About Mold in Buildings, When and How to Inspect for Mold, Clean Up Mold, or Avoid Mold Problems
Environmental Inspection, Testing, & Diagnosis On-Site IAQ, Gas, Air Testing, Mold Investigation, Sick Building Diagnosis, Lab Services, & Remediation Plan Preparation - indoor air quality testing, problem source determination, supporting lab work, written remediation plan addressing removal of environmental and other hazards and prevention of their recurrence.
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