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Thread: Staggered stud wall assemblies

  1. #1
    Join Date
    May 2007
    Location
    Baton Rouge
    Posts
    770

    Staggered stud wall assemblies

    I am currently working on a hotel that has 1-hr walls between all rooms with staggered studs for sound purposes.

    I have 4" sq. boxes for all the data drops and some receptacles.

    I have Allied fiberglass boxes for the majority of outlet/switch boxes.

    The fire marshall has accepted my documentation that putty pads are not needed for the Allied boxes installed as close as 3" in the same stud cavity on opposite sides of the wall.

    The fire marshall has not accepted my documentation from the IBC for metal boxes installed on opposite sides of the wall.

    Her interpretation is that the wall is one stud cavity.

    She will not accept the IBC, only Life Safety.

    The IBC clearly allows my installation as long as boxes are not directly back to back.

    Does anyone have experience with this?
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    Last edited by walkerj; 06-30-10 at 08:04 PM.
    Jason

  2. #2
    Quote Originally Posted by walkerj View Post
    I am currently working on a hotel that has 1-hr walls between all rooms with staggered studs for sound purposes.

    I have 4" sq. boxes for all the data drops and some receptacles.

    I have Allied fiberglass boxes for the majority of outlet/switch boxes.

    The fire marshall has accepted my documentation that putty pads are not needed for the Allied boxes installed as close as 3" in the same stud cavity on opposite sides of the wall.

    The fire marshall has not accepted my documentation from the IBC for metal boxes installed on opposite sides of the wall.

    Her interpretation is that the wall is one stud cavity.

    She will not accept the IBC, only Life Safety.

    The IBC clearly allows my installation as long as boxes are not directly back to back.

    Does anyone have experience with this?
    Name:  staggered.jpg
Views: 609
Size:  14.1 KB
    Even though you have given her the documantation, in the NFPA 220-1999 and NFPA 5000 it directly states that due to construction differences from locality to locality, the AHJ has the final word in deciding the final wall rating. I've been in a discussion with an inspector about a wall I considered to have a 15 minute fire rating, and he did not. In the end, I ahd to back down because of the way the wording is, it directly gives the AHJ the final decision
    It depends on what the meaning of "is" is.

  3. #3
    Join Date
    May 2007
    Location
    Baton Rouge
    Posts
    770
    Well the wall type is clearly stated on the fire Marshall approved stamped drawings.

    The wall type has been tested by ul in the exact manner we have on site.

    We have proved this in writing, but she wants putty pads on all metal boxes installed in these 30' long walls, some with up to six 4" sq boxes.
    Multiply that times forty walls on four floors and that is a lot of putty pads.

    It is just so aggravating because the simplest solution would be to put in a 2x6 stud, but the owner will not accept that.
    Jason

  4. #4
    Quote Originally Posted by walkerj View Post
    Well the wall type is clearly stated on the fire Marshall approved stamped drawings.

    The wall type has been tested by ul in the exact manner we have on site.

    We have proved this in writing, but she wants putty pads on all metal boxes installed in these 30' long walls, some with up to six 4" sq boxes.
    Multiply that times forty walls on four floors and that is a lot of putty pads.

    It is just so aggravating because the simplest solution would be to put in a 2x6 stud, but the owner will not accept that.
    Open the NFPA 5000 and look up your wall type that you say has been tested. Right under that, it says these construction types are examples only, and due to constrcuction differences, the AHJ makes the final decision.

    I was in your situation, and had to bow down gracefully and create an exit stratedgy to minimize losses. Like ot or not, it says what it says, which gives her the final decision. If she will not rate it at one hour, and you are required to have a one hour wall, somebody's gotta give. Good luck
    It depends on what the meaning of "is" is.

  5. #5
    By your diagram, I believe you're in violation of this code:


    (1) Any steel electrical box not exceeding 16 in.2 (10,300 mm2)
    in area shall be permitted where the aggregate area of the
    openings provided for the boxes does not exceed 100 in.2
    (64,520mm2) in any 100 ft2 (9.3m2) of wall area, and where
    outlet boxes are installed on opposite sides of the wall, the
    boxes shall be separated by one of the following means:
    (a) By a horizontal distance of not less than 24 in.
    (610 mm)
    (b) By a horizontal distance of not less than the depth of
    the wall cavity where the wall cavity is filled with cellulose
    loose-fill, rock wool, or slag wool insulation
    (c) By solid fireblocking in accordance with 8.14.2
    (d) By other listed materials and method


    Chapter 8 of NFPA 5000
    It depends on what the meaning of "is" is.

  6. #6
    Join Date
    Apr 2009
    Location
    VA
    Posts
    192
    I run into this all the time, and it always comes down to the AHJ's decision. A staggered stud wall does not have bays, and more times than not we wrap boxes with putty pads.

    Here's an article from 3M that you might find of some use:

    http://multimedia.3m.com/mws/mediawe...6EVs6E666666--

    also, from STI:

    http://www.stifirestop.com/product_i...ssp_putty.html

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