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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.

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.

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Outdoor Chimney Height & Clearance Requirements

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, our measuring tape is pulled to about four and a half feet.. And the height of the chimney above the roof surface should be at least three feet - the green line in our photo. (This is a bit of an odd measurement and chimney clearance case because the chimney side is actually about 8" away from the roof edge. But the chimney-to-roof clearance rules still apply.) This measuring tape location shown in 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 check the ten-foot clearance rule distance. That's the light blue line in our photo.

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). A horizontal line (blue in our photo) drawn from the chimney top to where it would touch the roof surface was just about one foot instead of the required ten feet OR two feet above the ridge.

The photo at above right is a too-short metal chimney that is less than two feet above the ridge. This chimney fails both the ten-foot rule (the blue line) and the two foot rule (the red line). A horizontal line drawn from the chimney top just touches the roof ridge.

Watch out: 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?

Too-Short Heating Flue Can Mean Sooty Oil Burners and Puffbacks

A too-short chimney is more than a fire hazard. It can mean that heating equipment venting into the chimney won't work properly, is unsafe, or is "forced" to work by settings that waste your heating money.

In response to owner pleas that no one had been able to fix this trouble, an oil company's service technician who worked on this flue in 2010 "solved" the long standing oil burner soot problem by setting the draft up as high as he could at the oil burner. That slowed but did not stop the sooting problem, and for sure it increased the heating cost for this building. Stack temperature was 600 degF (photo at left) - minus room temperature, making it about 530 - a bit high. We could have addressed this short chimney with a draft inducer fan, but a taller flue would be smart anyway, to get the chimney top higher than the roof surface. We discuss examples of extending chimney height to improve draft, performance, and fire safety separately at Chimney Height Extensions. We discuss draft inducer or "draft boosting" fans for heating systems (and maybe for some fireplaces) in detail at Draft Inducer Fans. Just how short is "too short" - we discuss chimney height and roof clearance requirements beginning below.

Required Chimney Height Above Roof Surfaces or Ridges

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

Frequently Asked Questions (FAQs) about chimney height & fire safety clearance requirements specified by building codes and best construction practices

Question: how to diagnose a smoky fireplace & chimney

Why would my fireplace smoke up the house during the time I have a fire. It's a masonry chimney. Also, my chimney is not 2 foot higher than the peek of the roof. - George Angell

Reply: "Why would my fireplace smoke up the house during the time I have a fire. It's a masonry chimney."

If your flue is cold it can take a while for the chimney to heat up enough to establish a good draft over a fireplace. To help things get going we often

• Make sure the damper is fully opened and that the chimney is not blocked and not damaged - hire a certified chimney sweep to inspect the flue for safety and to clean it if necessary.
• Light some newspaper placed at the back of the logs in the fireplace to help establish draft when you're first getting your fire going
• Make sure the ash pit door for your fireplace is closed = if the ash pit door is open air entering at that location will reduce draft seen in the fireplace. There may be ash pit doors both in the floor of the fireplace and also in the basement below the fireplace.
• Be sure that the chimney cap is properly installed and is the right type - a bad or missing chimney cap can cause bad draft as well as allowing downdrafts.
• Open a window or door near the fireplace so that there is plenty of good air flow into the room when you are lighting the fire - you can close this opening again once the fire is established.
• Best practice: after correcting chimney height, making sure the chimney flue is sound and not blocked or dirty, provide outside combustion air for your fireplace

RE: "my chimney is not 2 foot higher than the peek of the roof."

The chimney should be extended to be at least 2 feet above the ridge if the chimney is at or close to the ridge, or it should meet the height requirements shown in the sketch at page top.

If your chimney is too short it may not only result in inadequate draft (and improper heating system operation) but it can also be a fire hazard to the structure.

Question: Do we have to comply with chimney height clearance requirements for a 12/12 pitch roof? Does a power-vent flue excuse chimney height requirements?

We gave a 12/12 pitched roof and want to put a wood burning stove near the outside edge of the house (not near the peak) - is there ANY configuration of chimney that will not have 12 feet (or more) of pipe sticking out of the roof line?

Routing the chimney flue pipe toward the peak is not really an option it would basically have to come up near the outside eaves - clearing 2 feet any roof surface within 10 feet means at least 12 feet of pipe as far as I can tell. Are powered chimney vents an option? - Matt

Reply:

Matt: a line drawn horizontally from the top of the chimney to a point where that line would touch the roof surface needs to give you ten feet in distance for fire safety. If your roof pitches up steeply that may mean you need a rather high woodstove chimney to be safe. And you may need bracing.

I've not found references to power vent exhausts for woodstoves. Certainly it is not at all likely that a power-vented chimney would be more fire safe and thus would not need the same fire clearances as other chimneys and flues.

Question: What is the chimney clearance from the chimney pipe to a second story window?

i have a two story home. i just built a single story room off this home with a wood stove. what is the clearance from the chimney pipe to 2nd story window? it is already 2 feet above the ridge and 12 feet from the 2nd story windows - Charlie

Reply:

Charlie I'm not sure I understand the picture and measurements of the addition you describe. If your chimney is two feet above the ridge of the upper roof it would certainly not be too close to any windows.

If your chimney is two feet above the ridge of a roof over the one story addition, if you can't get more than 12 feet of horizontal distance between chimney and windows of the upper floor, you probably need to extend the chimney above the upper roof, following the ten-foot horizontal line rule we describe above.

Otherwise in at least some conditions, someone is going to open an upper floor window and find smoke blowing into the room.

Question: We're adding a roof whose ridge will abut the existing chimney. How does that affect chimney height clearance requirements?

I want to add a pitched roof to an existing home for a screened in porch. The point of the gable would go up against the existing chimney. Is that acceptable as long as the point of the gable (the highest point of the addition) is still 3.5 feet below the top of the chimney?

Reply:

Dave that sounds OK to me, just be sure to properly flash against the chimney or you'll have leaks. That is, if the ridge of the lower roof, where it abuts the existing chimney, is three feet or more below the chimney top, you've met that clearance requirement (the three-foot chimney clearance rule).

Question: My masonry chimney extend 2' above the top of the pitch. Does it have to be extended to 3'

My masonry chimney extend 2' above the top of the pitch. Does it have to be extended to 3' above to comply with the NBC? - Frank

Reply: here is a summary of chimney code and fire clearance rules: the two-foot, three-foot, ten-foot rule for chimney heights:

Frank,

Some building code officials, builders, and chimney professionals call this simple chimney fire clearance code the
"two-foot, three-foot, ten-foot rule for chimney heights" - which we explain as follows:

Your chimney top to roof clearance (for fire safety) is correct if the chimney height extends:

• The two-foot chimney rule: The chimney top must be two feet above the ridge of the roof (If the chimney is at or very close to the ridge) This is the red line at the right side of our chimney height sketch above.
• The three-foot chimney rule: The chimney top must be three feet (or more) above the roof surface (measured right next to the chimney, at the up-slope side of the chimney). This is the vertical green line in our chimney clearance sketch above.
• The ten-foot chimney rule: The chimney top must be high enough above the roof surface such that a horizontal (level) line drawn from the chimney top to the nearest roof surface will run ten feet or more before that line touches the nearest (up-slope) roof surface. The ten foot chimney height rule is illustrated by the blue line in our sketch above.

Take a look at the chimney height clearance requirements sketch at the top of this page. The only confusing detail in that sketch is that the "ten foot chimney height rule" horizontal line was shown as drawn mid way down the chimney - really that line is drawn from the chimney TOP to the nearest roof surface.

Question: My A-Frame chimney is just one foot above the roof if measured at the ridge - do I need to extend it

I have an "A" frame cottage with a new metal roof. The woodstove has a 10" insulated metal chimney which extends above the roofline by approx 7 ft. and is above the peak by maybe 1 ft.

Reply: details of the ten-foot rule for chimney distances from nearby roof surfaces

Bruce:

Ok, so technically your flue is one foot short; perhaps given the very steep roof and that it's metal, I'm not as worried as I'd be otherwise, but it's possible that the chimey is not fire safety and code compliant for a second reason: if you were to draw a horizontal line from your chimney top towards the ridge, and if the horizontal distance from the top to the ridge is less than 10 feet, then properly your chimney needs to go up another foot.

On the other hand if the horizontal distance from your chimney to the ridge is ten feet or more, you're ok as is.

At CHIMNEY HEIGHT & CLEARANCE CODE you can find articles on required chimney heights above the roof line.

Questions & Answers regarding this article

Questions & answers about chimney height & clearance requirements to comply with building codes and fire safety.

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CHIMNEY HEIGHT & CLEARANCE CODE
  Adjacent Metal Chimney Separation
  B-Vent Clearances Table
  Chimney Too Short
  Chimney Height Extensions
  Chimney Height for Types L & Type B Vents
  Fire Clearances for Masonry Chimneys
  Fire Clearances for Metal Chimneys
  Fire Clearances, Single-Wall Metal Flues
  Masonry Chimney Roof Clearance
  Wood burning Fireplace Roof Clearance
Chimney Height Extensions

• Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. Thanks to Alan Carson and Bob Dunlop, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education including the ASHI-adopted Home Inspection Training Program (home study course), publications such as the Home Reference Book, report writing materials including the Horizon report writer, 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
• 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
• 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 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.
• Fireplace & Chimney Design, Repair Books - Fireplaces, Chimneys: design, repair
• Fireplace & Chimney Inspection Books - Inspecting and diagnosing chimney problems, fireplace problems, chimney & fireplace standards
• 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 211: Standard for Chimneys, Fireplaces, Vents, and Solid Fuel-Burning Appliances, 2006 Edition (older editions and standards are found at the same bookstore)
• Principles of Home Inspection: Chimneys & Wood Heating (Principles of Home Inspection), Carson Dunlop
• 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
• ...