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    Light boxes above acoustical ceilings

    Light boxes above acoustical ceilings

    New postby tmaxey on Thu Apr 30, 2009 4:27 pm

    As a Specifier, I am updating our master guide specs and have found an option in the Acoustical Ceiling spec that allows the use of acoustical ceiling panel materials to be used to make fire rated light boxes for the back of fixtures exposed above the ceiling. Is it my understanding that this should be done with drywall only or are the ceiling materials acceptable to use for site built boxes?

    Thank you.
    tmaxey
     
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    Re: Light boxes above acoustical ceilings

    New postby Jerry Peck - Codeman on Thu Apr 30, 2009 8:47 pm

    The reason gypsum board works, and is approved for that use, is because when the five-sided boxes are constructed properly, the fire-resistive rated membrane effectively "goes around" the recessed light fixtures and other items penetrating the fire-resistive rated membrane, be it a ceiling or a wall.

    I specifically stated "constructed properly" as many I have seen were not constructed as required to maintain the fire-resistive rating of the membrane and required replacement with new ones constructed properly.

    To be constructed properly, and effectively take the fire-resistive rated membrane around the penetration, the five-sided box needs to be constructed of the same gypsum board material (Type X or other fire resistive rated gypsum), of the same thickness, and the same number of layers, and, in the case of multiple layers, also have the edges shiplapped, with the same framing and fastening as required for, and used for, repairs to that fire-resistive rated membrane.

    I.e., the gypsum is attached to framing around all edges and to the ceiling or wall membrane, and, when multiple layers, the membrane is actually cut out for the larger five-sided box size opening, the edges shiplapped, all joints mudded, taped and sealed as required for the membrane's fire-resistive rating, then the opening (now no longer part of the fire-resistive rated membrane) is covered over and patched, with the recessed light or other item within that five-sided box.

    When recessed lights are enclosed in those five-sided boxes the recessed lights are required to be IC rated even though they are not in an insulated ceiling, this is because the ventilation required for a non-IC rated recessed light fixture is no longer provided, the recessed light fixture is in the sealed five-sided box with no ventilation - just as though it were enveloped in, and covered with, insulation.

    I covered the above in detail to set the stage for the following answer to your question.

    tmaxey wrote:As a Specifier, I am updating our master guide specs and have found an option in the Acoustical Ceiling spec that allows the use of acoustical ceiling panel materials to be used to make fire rated light boxes for the back of fixtures exposed above the ceiling. Is it my understanding that this should be done with drywall only or are the ceiling materials acceptable to use for site built boxes?


    I would have to see the specifications on that acoustical material and the UL design which allows for it to serve the purpose of enclosing the five-sided box as stated above. And, if that material is approved for that use, the UL design for its use would include the framing and attachment required for it use.

    I.e., just like gypsum board is not supposed to be, is not allowed to be, just screwed or glued together and set on the fire-resistive rated ceiling over the recessed light or other penetration and needs to be properly secured in place to maintain the fire-resistive rating, the acoustical material, if allowed to be used, would also require the framing and attachment the other acoustical material in that fire-resistive rated membrane is required to have.

    If you have a fire-resistive rated acoustical ceiling assembly and the five-sided box is constructed, supported, and attached in the same manner as the rest of the fire-resistive rated acoustical ceiling, maybe it would be approved for that use under the above construction conditions I mentioned as the fire-resistive rated membrane would now be going around the recessed lights or other penetrating items, making the items no longer penetrating the fire-resistive rated membrane.

    Do you have a link to that acoustical ceiling material and the specification you are referring to?

    That should answer the questions I have, and am posing, regarding its use as a five-sided box covering membrane penetrations such as recessed light fixtures.
    Jerry Peck - CodeMan
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    Re: Light boxes above acoustical ceilings

    New postby Jerry Peck - Codeman on Tue May 19, 2009 10:32 am

    From everything I have found the acoustic ceiling tile is approved for that use *in that acoustic ceiling tile system ONLY*.

    I also understand the reasoning for allowing it – there is no need to have the five sided box which is *more* fire-resistant than the ceiling system it is in. The membrane penetration does not require a greater fire-resistant rating than the membrane has.

    Makes sense in a logical way, but then I’ve never liked the thought of using acoustic tile as a fire-resistant rated system anyway – but who am I compared to all the knowledgeable people who design, test, list and label those systems – they figure out the minimum which will work, construct the test sample perfectly, pass the test with conditions which do not always replicate real life, then give the system a thumbs up … knowing that construction is never done perfectly as required.

    The key, of course, is that the installation/construction of the acoustic tile five sided box must be done in accordance with a UL Design for that fire-resistant rated system – it cannot just be slapped up there however the installer chooses to slap it together.
    Jerry Peck - CodeMan
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