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  1. #1
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    Default Height of Type B Vent on Roof

    I'm reading some literature on the height required for a B-vent above a roof surface and I just want to make sure I'm understanding this correctly. Based on the pitch of the roof in the attached pic, the vent pipe needs to extend at least 1' above the roof surface which it does (31" is what I measured). What I'm unclear of is if it's proximity to the ridge factors in and requires any additional extension of the height of the flue pipe. The distance I measured from the pipe to the ridge was 4'5".

    Is this OK as is or is an extension required? The only excecption I can find if the flue pipe is within 8 feet of a vertical surface.

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  2. #2
    Ray Norton's Avatar
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    Default Re: Height of Type B Vent on Roof

    That installation is compliant. Only installations not found on the chart (where you found the 12-inch requirement) would have to be 2 feet higher than anything within 10 feet. This is a frequent occurrance for me as a municipal building inspector and mechanical plan examiner.


  3. #3
    Jerry Peck's Avatar
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    Default Re: Height of Type B Vent on Roof

    Type B Gas vents less than 12 inches in diameter:
    - 1) Shall terminate at least 5 feet above the draft hood of the highest appliance connected to the vent.
    - 2) The attached table is the minimum height above a roof for vents not located within 8 feet of a vertical wall or similar obstruction.
    - 3) If the vent is within 8 feet of a vertical wall or similar obstruction then the vent needs to be: a) not less than 2 feet high on the high side where it comes through the roof (do not use the table I've attached), AND: b) not less than 2 feet higher than any portion of the building within 10 feet horizontally.

    Note that the second drawing attached says to refer to Table 2, the table I've attached.

    Keep in mind that 3) and the 2 feet higher than any portion of the building within 10 feet DOES NOT become a factor if there is no vertical wall or similar obstruction within 8 feet - that the attached table can be used.

    In the photo, there is no vertical wall or similar obstruction within 8 feet, so use the attached table.

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  4. #4
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    Default Re: Height of Type B Vent on Roof

    Thanks guys.

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  5. #5
    Marc M's Avatar
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    Default Re: Height of Type B Vent on Roof

    Quote Originally Posted by Jerry Peck View Post
    Type B Gas vents less than 12 inches in diameter:
    - 1) Shall terminate at least 5 feet above the draft hood of the highest appliance connected to the vent.
    - 2) The attached table is the minimum height above a roof for vents not located within 8 feet of a vertical wall or similar obstruction.
    - 3) If the vent is within 8 feet of a vertical wall or similar obstruction then the vent needs to be: a) not less than 2 feet high on the high side where it comes through the roof (do not use the table I've attached), AND: b) not less than 2 feet higher than any portion of the building within 10 feet horizontally.

    Note that the second drawing attached says to refer to Table 2, the table I've attached.

    Keep in mind that 3) and the 2 feet higher than any portion of the building within 10 feet DOES NOT become a factor if there is no vertical wall or similar obstruction within 8 feet - that the attached table can be used.

    In the photo, there is no vertical wall or similar obstruction within 8 feet, so use the attached table.
    Is this an obstruction?

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  6. #6
    Jerry Peck's Avatar
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    Default Re: Height of Type B Vent on Roof

    Quote Originally Posted by Marc M View Post
    Is this an obstruction?
    Yes.

    If there is a vertical wall or similar obstruction (that is similar and is even a vertical wall) and which is within 8 feet (that is within 8 feet), then the vent needs to be 2 feet higher than the wall AND 2 feet higher than the sloping roof within 10 feet in the other directions. Not sure that is the intent of this as related to your photo, but that is what the wording says ... one would think that if the sloping roof was okay within 10 feet without that vertical wall, that being 2 feet higher than that vertical wall would solve the problem without regard to the sloping roof - of course, though, being 2 feet higher than that chimney would likely put also put it 2 feet higher than the sloping roof within 10 feet ...

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  7. #7
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    Default Re: Height of Type B Vent on Roof

    Nick,

    I'm going to try a different approach here.

    What is that B- (L- or Special) Vent system termination pictured actually providing venting for (and where is it/are they located)?

    Is that a continuous ridge vent opening under the ridge cap shingles? What is directly below the roof deck (enclosed attic space(s) or enclosed rafter space(s) perhaps? If so, what is the nature of the ventillation system for the space(s) being ventillated?

    What are those white vertical open possibly PVC pipe, booted, roof penetrations ("other obstructions") functioning as? Plumbing vent terminals perhaps? (Also, can't make out the markings - what trade size are they, what are the Standards listed on the red markings?), and how close are they horizontally and opening elevation from the lowest and closest discharge opening of the Listed B-, L-, or Special Vent cap? Both their roof penetrations appear "uphill" of the B-vent and approximately the same or similar distance, horizontally, from the Vent Cap, is that what the picture is demonstrating?

    What is the 97.5-percent value for outside design temperature for the region?

    You do have frost sometimes, and even snow, isn't that right?

    What is the anticipated snow accumulation height for the region?

    Is this the lee side of the structure?




    Side note: Didn't catch a reference for what I presume was being represented as the table contained in IRC Figure G2427.6.4 (503.6.4), but I'm concerned that it is not, unless its one locally ammended, however unlikely, since the "image" references a "dura cap" I suspect it is an outdated and old image and "table" from manufacturer's materials if it is puporting to be representative of the IRC or IIGC. For example, IIRC Unammended '06 & '09 indicated

    Roof Slope ranges flat to 6/12 (not 7/12) H(eight) (min) ft = 1.0
    .......................over 6/12 to 7/12 H(eight) (min) ft = 1.25
    .......................over 7/12 to 8/12 H(eight) (min) ft = 1.5...
    ...and so forth.







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