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Type B-Vents Chimney Rooftop Clearances
Type B gas vents fire clearances at rooftop
- POST a QUESTION or COMMENT about B-vents chimneys & flues: installation specifications
Metal B-Vent chimney clearance distances above and on the roof:
Clearance distances are given for a gas appliance B-vent at the rooftop.
This article series describes B-vent metal chimneys used for gas-fired appliances. We discuss fire safety, fire clearances, and other gas appliance venting details for b-vent chimneys.
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Type B Gas Vent Rooftop Chimney Height & Clearances
Heights for these both B-Vent and L-Vent types of metal chimney vents are shown in Carson Dunlop Associates [at REVIEWERS] sketches at page top and right here.
[Click to enlarge any image]
The top of the chimney should be at least two feet above anything within a ten-foot radius of the chimney.
Except for flat and very low slope roofs such as those listed in the table below, B-Vents should be at least two feet above the roof surface as well.
See the detailed B-vent chimney rooftop clearance table below.
Also see CHIMNEY HEIGHT & CLEARANCE CODE - separate article that compares the B-vent with other chimney types.
The 1992 Vent Sizing Tables below (and more-recent codes) all 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.
Table of Type B-Vent Rooftop Clearance Requirements
Vent caps 12" and smaller may terminate a distance above the roof if 8 feet or more away from a vertical surface as follows:
| Table of Rooftop Chimney Clearances for Metal B-Vent Chimneys & Flues | |
|---|---|
| ROOF PITCH - rise/run in inches | Minimum Height Above the Roof Surface (1) |
| Flat to 7/12 | 1.0 foot above the roof surface (1) |
| 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 | |
Notes to the table above
- measure on the up-roof or "shorter" height side of the chimney
- Watch out: while one foot above the roof surface may meet the recommendations for fire clearances, in one-storey buildings or in buildings with heating equipment on the uppermost floor, the total chimney height may be inadquate to establish sufficient and safe draft unless you extend the chimney height by more than these low minimums.
- Chimney 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.
- 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.
- Details about chimney height & rooftop clearance requirements on buildings for all types of chimneys are
at CHIMNEY HEIGHT & CLEARANCE CODE
For details about all types of metal chimneys
see METAL CHIMNEYS & FLUES - The minimum distance from the top or nearest B-vent chimney component to overhead electrical wires is 3 ft.
See ELECTRICAL SERVICE DROP
...
Reader Comments, Questions & Answers About The Article Above
Below you will find questions and answers previously posted on this page at its page bottom reader comment box.
Reader Q&A - also see RECOMMENDED ARTICLES & FAQs
On 2020-10-07 - by (mod) -
There are model or standard prototype building codes that are written at a national level for most countries. State or provincial for local building authorities generally will adopt one of those models and occasionals make some adjustments to them.
If you look in the article index for this page you will find a link to all of the US and Canadian as well as other countries building codes and model codes
On 2020-10-07 by Model
Hi what did you mean by model?
Thanks,
Bob
On 2020-10-06 - by (mod) -
Robert
You're right, chimney heights, or minimum heights above the roof are described in model and local building codes.
On 2020-10-06 by Robert Fleszar
Hi,
I live in the middle unit of a 6 unit townhome with an HOA. I discovered a building code violation and want to correct it and replace a damaged vent pipe and B Vent Cap. The HOA is giving me a hard time wanting to know how high the new pipe will be.
I never heard of an HOA having that control or rule. I thought the height was distracted by the local code?
On 2020-03-10 - by (mod) -
No, Lee, for fire safety there are rooftop clearances given in the article above on this page.
For other readers, Lee's "POC" refers to "products of combustion.
On 2020-03-10 by Lee
Should the height be any hieght as long POC are adequately dispersed
On 2019-10-31 - by (mod) -
The possible concern is for both fire safety (clearances to combustibled) and fatal flue gas leak safety (if the system leaks).
Flexible flue vent connector material, presumably stainless steel) will be single-wall in thickness and even if code-approved to connect a fireplace vent, depending on the temperatures involved, it probably doesn't have the same combustible clearance ratings as a B-vent.
Pretty much everything depends on the specific type, brand, model of gas fireplace being installed. Get installation instructions and parts approvals in writing from the manufacturer.
On 2019-10-31 by Wendy
I have a gas fireplace insert with a flex pipe, and a B Vent at the roof. The insert needs replacing. I see the B Vent at the roof and, when I pull the insert forward a bit, I see a flex pipe out the top of the insert. The fireplace guy tells that B Vent into a flex pipe is bad/illegal. The fuel company/fireplace guy tells me he has never heard of this. Is there a concern?
Wendy
On 2017-11-03 - by (mod) -
Tom, at ADJACENT METAL CHIMNEY SEPARATION https://inspectapedia.com/chimneys/Chimney_Height_Codes_Specifications.php#AdjClr
we note that metal chimneys should be at least 16" (that's 16 inches) apart and that it makes sense to stagger the rain cap heights as well - I agree with your chimney contractor.
On 2017-11-03 by Tom
I have a B vent that was vented by the heating company in a new chimney chase adjacent to a metal chimney flue. The idea was to make a nice, clean look, and not have another hole in the roof. The chimney contractor says I should be concerned about the short distance (about 5 inches) between the two caps due to downdraft into the fireplace. I can't find anything that tells me there's a minimum(?), but I am concerned. Any suggestions?
...
Continue reading at HEIGHT REQUIRED for L VENTS & B VENTS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.
Or see TYPE B-VENT CHIMNEY FAQs - questions & answers posted originally on this page
Or see these
Recommended Articles
- ADJACENT METAL CHIMNEY SEPARATION - separation between metal chimneys and their rain caps
- CHIMNEY WET TIME & CORROSION for a discussion of causes of corrosion in B-vents and other metal chimneys
- HEIGHT REQUIRED for L VENTS & B VENTS
- METAL CHIMNEYS & FLUES - home
- METAL CHIMNEY INSTALLATION MANUALS
- TYPE B-VENT CHIMNEYS - home
- TYPE B VENT vs L VENT DIFFERENCES
- TYPE B-VENT CEILING FLOOR WALL CLEARANCES
- TYPE B-VENT ROOFTOP CLEARANCE
Suggested citation for this web page
TYPE B-VENT ROOFTOP CLEARANCE at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.
Or see this
INDEX to RELATED ARTICLES: ARTICLE INDEX to CHIMNEYS & FLUES
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Citations & References
In addition to any citations in the article above, a full list is available on request.
- 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 [Website: /www.house-whisperer.com ] 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 804-873-8534 or by Email: johncranor@verizon.net
- Thanks to Luke Barnes for suggesting that we add text regarding the hazards of shared chimney flues. USMA - Sept. 2008.
- Arlene Puentes [Website: www.octoberhome.com ] , 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 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 - 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: CHIMNEY INSPECTION DIAGNOSIS REPAIR . Copies of earlier editions of the ASHI Technical Journal are available from ASHI, the American Society of Home Inspectors.
- "Chimneys and Vents", 789 CMR 68.00 Massachusetts Building Code, web search 10/15/2010, original source:
http://www.mass.gov/Eeops/docs/dps/780%20CMR/780068.pdf 03/23/2007
780 CMR: STATE BOARD OF BUILDING REGULATIONS AND STANDARDS THE MASSACHUSETTS STATE BUILDING CODE - quoting:
6801.11 Multiple-Appliance Venting Systems. Two or more listed and labeled fossil fuel-fired appliances shall not be connected to a common natural draft venting system unless permitted per applicable requirements of 248 CMR or 527 CMR. For solid fuel-burning appliances, see 780 CMR 6801.12. - Chimneys and Vents, Chapter 18, M1801,model building code - [on file as Code_Chim_Res_C_18.pdf] - widely used by U.S. & Canadian Municipalities,
- "Model DFS L-Vent / Type B Gas Vent Installation Instructions", Selkirk Corporation, 5030 Corporate Exchange Blvd., Grand Rapids MI 49512, Tel: 800-433-6341 & Selkirk Canada Corporation, PO Box 526, Depot 1, Hamilton ON L8L 7X6, 888-735-5475, web search 10/15/2010, original source: www.mass.gov/Eeops/docs/dps/780%20CMR/780068.pdf
- "Type L Temperature Venting Systems [on file as L_Vent_Metal_Fab.pdf] - ", Installation and Maintenance Instructions, Metal-Fab Inc., PO Box 1138, Sichita KS 67201, 316-943-2351, Email: info@mtl-fabinc.com website: www.mtl-fabinc.com
- "Type L Vent Vent for Oil/Gas Fired Appliances, Installation and Maintenance Manual", Energy Vent Ltd., 241 Arvin Ave., Stoney Creek Ontario Canada L8E 2L9, web search 10/15/2010 original source: www.selkirkcorp.com/WorkArea/downloadasset.aspx?id=2380 www.selkirkcorp.com/WorkArea/downloadasset.aspx?id=1802
- Natural Gas Weekly Update: http://tonto.eia.doe.gov/oog/info/ngw/ngupdate.asp Official Energy Statistics from the U.S. Government
- 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. - 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.
- 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, in (Principles of Home Inspection), Carson Dunlop, Associates, Toronto, Ontario
- 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
- In addition to citations & references found in this article, see the research citations given at the end of the related articles found at our suggested
CONTINUE READING or RECOMMENDED ARTICLES.
- Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: info@carsondunlop.com. 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 - the Encyclopedia of Homes and to use illustrations from The ILLUSTRATED HOME .
Carson Dunlop Associates provides extensive home inspection education and report writing material. In gratitude we provide links to tsome Carson Dunlop Associates products and services.
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