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    combustion air in garage

    combustion air in garage

    New postby Bungalows on Tue Feb 10, 2009 10:03 am

    Codeman,

    I wrote up a non ducted combustion air vent in the attached garage ceiling, just a hole with a return air grill, as in violation of the seperation barrier, and further recommended that it be ducted to the outside, not into the attic but outside.
    The county code guy, AHJ, said that if it is ducted with metal to the top of the bottom chord it is ok. WTF
    When I asked about the seperation he told me it was not a problem.
    So Jerry, whos on crack?
    Bungalows
     
    Posts: 12
    Joined: Tue Feb 03, 2009 5:19 pm

    Re: combustion air in garage

    New postby Jerry Peck - Codeman on Tue Feb 10, 2009 11:33 am

    Being as you did not provide what state you are in, I will provide an answer based on the 2006 IRC, presuming the building falls under the IRC as reference was made to "separation barrier", which would apply to dwelling unit residences and their attached garages.

    A non-ducted combustion air vent is simply a "hole through the ceiling" which allows air to flow through to replace air used for combustion. From your post the AHJ inspector said that if you duct it for the distance from the bottom of the ceiling to the top of the bottom chord of the truss it would be okay.

    As I see it, the AHJ inspector simply asked you to "line the hole through the ceiling" with metal, right? Did he at least specify 26 gage? Not that 26" wrapped around the perimeter of the hole would do any good.

    I'll make some presumptions from your description and base my answer on those presumptions.

    The garage/residence wall is discontinuous in the attic (does not continue to the bottom of the roof sheathing), thus the garage ceiling is used to provide the required separation between the garage and the residence's attic as required by code:
    -> From the 2006 IRC. (underlining and bold are mine)
    - -> R309.2 Separation required. The garage shall be separated from the residence and its attic area by not less than 1/2-inch (12.7 mm) gypsum board applied to the garage side. Garages beneath habitable rooms shall be separated from all habitable rooms above by not less than 5/8-inch (15.9 mm) Type X gypsum board or equivalent. Where the separation is a floor-ceiling assembly, the structure supporting the separation shall also be protected by not less than 1/2-inch (12.7 mm) gypsum board or equivalent. Garages located less than 3 feet (914 mm) from a dwelling unit on the same lot shall be protected with not less than 1/2-inch (12.7 mm) gypsum board applied to the interior side of exterior walls that are within this area. Openings in these walls shall be regulated by Section R309.1. This provision does not apply to garage walls that are perpendicular to the adjacent dwelling unit wall.

    The AHJ inspector has just stated that the required separation is not required in the hole through the garage ceiling (however large that hole through the garage ceiling is), "the hole through the garage ceiling is a violation of the above code section.

    How do you solve that problem?

    There are several options, listed in order of preference:
    -> 1) The combustion air could be ducted through the wall to the outdoors. Air travels easier horizontally than vertically, option 2) below.
    -> 2) The combustion air could be ducted through the ceiling, up and out through the roof, using minimum 26 gage metal duct.
    -> 3) It may be possible to install a fire damper in the hole through the ceiling which will close when there is a fire, however, that could cause the appliances depending on that combustion make-up air to begin drawing that combustion air from elsewhere. To prevent this, a switch may be able to be installed which would shut the fuel burning equipment down when the fire damper closes. Of course, though, the switch, an damper would all need to be listed and labeled for that purpose, so just 'rigging up a switch to a damper' is not going to be acceptable.

    You stated that "When I asked about the separation he told me it was not a problem.", of course he is correct ... "the separation" is not a problem, however, "the LACK OF separation" is a problem. Not only is the lack of separation a problem, it is also a code violation.

    Which inspector did you talk with: the building inspector or the mechanical inspector?
    -> I can imagine the mechanical inspector saying something like that as that is his view point - he is looking for something which provides for combustion make-up air, and it was there. You raised a concern about fire so he said wrap the hole in metal duct where the wood is.
    -> I cannot imagine the building inspector saying that was okay.

    I would re-state your concerns and explanations to the county inspector in such a way that you are not questioning his/her opinion, but that you are trying to clarify your thinking with that opinion. Most code inspectors do not like to be challenged, however, many are open to helping you understand what needs to be done and why, and during the course of that discussion, they may realize just what it is you are saying.

    Codeman
    Jerry Peck - CodeMan
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    Re: combustion air in garage

    New postby Bungalows on Tue Feb 10, 2009 11:45 am

    Thanks Jerry, that was pretty much what I thought. I am in Gainesville by the way.
    Thanks for putting up this website, you are a gentleman and a scholar
    Bruce
    Bungalows
     
    Posts: 12
    Joined: Tue Feb 03, 2009 5:19 pm

    Re: combustion air in garage

    New postby Jerry Peck - Codeman on Tue Feb 10, 2009 12:02 pm

    Hi Bruce,

    As you are in Gainesville, Florida, I will post the 2004 Florida Building Code, Residential, w/2006 Revisions, section applicable to dwelling unit and their attached garages.

    From the 2006 FBC, Residential, w/2006 Revisions. (underlining and bold are mine)
    -> R309.2 Separation required.
    - -> The garage shall be separated from the residence and its attic area by not less than ½-inch (12.7 mm) gypsum board applied to the garage side. Garages beneath habitable rooms shall be separated from all habitable rooms above by not less than 5/8-inch (15.9 mm) Type X gypsum board or equivalent. Where the separation is a floor-ceiling assembly, the structure supporting the separation shall also be protected by not less than ½-inch (12.7 mm) gypsum board or equivalent.

    If not identical language to the IRC, it is very close because it is based on the IRC.

    Thank you and I look forward to being of help in the future.

    Codeman
    Jerry Peck - CodeMan
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    Construction Litigation Consultants, LLC.
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