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installing wood sleepers over exisitng concrete slab that need 2 hour fire rating

Discussion in 'Commercial Building Codes' started by sal, Jul 17, 2017.

  1. sal

    sal Member

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    I have a condition that has a mechanical room below a dwelling unit. The ceiling of the mechanical room is a solid 4"concrete slab. I believe the fire rating needs to be 2 hours which we may be shy of with 4"

    The design calls for sleepers above the concrete slab. Would filling the spaces between the sleeps with roxul insulation be a good option, or would this reduce the fire rating of the floor. I know adding insulation can reduce fire ratings.

    Any good solutions here?
     
  2. RLGA

    RLGA Sawhorse

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    Typically, if the assembly supporting the wood flooring provides the required fire-resistance rating, then what's added on top is of no consequence. The only exceptions to this is for Type I and II construction, upon which the IBC places some added restrictions (See Section 603 and Section 805).

    The type of concrete used will have a bearing on the determination of the concrete's fire resistance. Refer to IBC Table 721.1(3) for items 1-1.1 through 4-1.1. Most likely, the concrete (if unsupported by other construction) is of items 1-1.1 or 2-1.1, meaning a 4-inch slab is not providing enough material to achieve the required fire-resistance rating. You may be able to add material below the slab to improve the floor assembly's fire-resistance rating.

    What is supporting the concrete slab? Is it on metal deck with steel joists, or is it spanning between concrete beams? If the latter, is the concrete post-tensioned? These questions will also factor into the fire resistance of a floor assembly.
     
  3. sal

    sal Member

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    It is an existing reinforced concrete slab formed into concrete foundation walls. No way for me to know what type of concrete it is, I supposed I should assume the worst which I believe is siliceous aggregate?

    Do you think it is just existing construction that can be left alone (The sleepers not considered to be altering the floor assembly, just something cosmetic)
     
  4. RLGA

    RLGA Sawhorse

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    Is the 2-hour rating new due to change of occupancy or alteration of existing space, or was that the requirement at the time of construction? If the requirement was 2 hours at the time of construction, then you have an entirely separate issue with an existing noncompliant situation (but still needs to be corrected, but the owner may have a claim against another party to recover costs for correcting the situation).

    Have you measured the thickness of the existing slab or are you basing the thickness off of record drawings? If using record drawings, I suggest finding out exactly what the existing thickness is and work from there--who knows, maybe it was corrected in the field and the record drawings were not annotated to reflect the change. You can add thickness by placing a topping on the existing slab; however, this may require approval by the B.O. If you do not want to add more material on the top side of the slab, UL has several assemblies where you can spray-apply fire-resistive material to the underside of the concrete.
     
  5. sal

    sal Member

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    I suppose spray would be easiest.

    We are altering the dwelling unit above the mechanical room. The floor was stripped off on the concrete slab and the wood sleepers were added. (they are there now so would like to avoid topping slab...)

    I suppose I should point all this out to the building official since we are currently in construction.
     
  6. cda

    cda Sawhorse

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    Welcome!!!!
     
  7. ADAguy

    ADAguy Sawhorse

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    I hear no mention of whether either floor is sprinklered?
     
  8. sal

    sal Member

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    no, no sprinklers. VB construction
     
  9. sal

    sal Member

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    so, i found "firefree88" and incitement spray and they will send me documentation of how the slab rating can be upgraded.

    The question now is those sleepers, should they be fire treated wood? can roxul be put on top of the slab, between the joists without consequence? (the inspector may want
    insulation for stc 50)
     
  10. ADAguy

    ADAguy Sawhorse

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    Shame the guy didn't use metal studs to begin with. Firefree is good stuff, it is intumescent.
     
  11. RLGA

    RLGA Sawhorse

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    I suggest looking at actual UL assemblies for spray-applied fire-resistant coatings applied to concrete floor assemblies. The product you mentioned does not appear in any UL assemblies (that I could find) for the conditions you describe.
     

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