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L vent and B vent height requirements (C) Carson Dunlop Associates Type B-Vents Chimney Rooftop Clearances
Type B gas vents fire clearances at rooftop

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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

Type B Vent (C) Carson Dunlop Associates

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

(1) measure on the up-roof or "shorter" height side of the chimney

(2) 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.

(3) 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 is at CHIMNEY HEIGHT & CLEARANCE CODE

For details about all types of metal chimneys see METAL CHIMNEYS & FLUES

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Continue reading at HEIGHT REQUIRED for L VENTS & B VENTS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see TYPE B-VENT CHIMNEY FAQs

Or see METAL CHIMNEYS & FLUES - home

Or see CHIMNEY WET TIME & CORROSION for a discussion of causes of corrosion in B-vents and other metal chimneys

Or see this

Article Series Contents

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.

INDEX to RELATED ARTICLES: ARTICLE INDEX to CHIMNEYS & FLUES

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