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What is the Fire Rating for a low roof?

Discussion in 'Existing Buildings Codes' started by kas, Nov 6, 2019.

  1. kas

    kas Member

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    Existing 3 story 12 inch thick brick bearing wall, wood framed- mixed use - 2 floor residential over commercial space under going change of occupancy Mercantile to Business.

    Under IEBC, change to lower hazard, the existing rating of exterior walls is ok.

    Low roof rating?

    The first floor goes from side to side property lines. 2nd and 3rd have inset 5x10 courts to give light to windows.
    Would like to run grease and make up air duct work from 1st floor thru the roof/floor of one of those courts up side of building to new equipment on roof.

    Existing parapet is 12 inches high.

    How to figure out the fire rating of that roof?

    Thanks
     
  2. RLGA

    RLGA Sawhorse

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    What is building area of the 1st story, 2nd story, and 3rd story?
     
  3. steveray

    steveray Sawhorse

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    So.....The exterior walls are party walls? What are their fire ratings? 10' back 1hour rating rings a bell (for stepped buildings), but I would have to spend some time looking....Ch. 7 is your friend...
     
  4. kas

    kas Member

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    rlga-

    39 ft tall
    ground floor - 1746 sf
    2nd/3rd 1631 sf each

    steveray

    they are zero lot line walls.

    the interplay between the IBC and IEBC and required ratings is tricky.

    IEBC-under chapter 10, change of occupancy- bc lesser hazard, ext wall fire resistance is accepted.By adding the duct penetrations, I am not changing the existing wall/roof.

    IBC-
    existing walls are 12 inch brick- assume min 2 hr

    if consider the existing construction 5B- meet area and height but not story.
    3B- meet both-

    roof as 0hr either 3b or 5b
    walls need to be 1hr bc of distance from property line

    i am being told that bc parapet is less than 30 inches, the low roof needs to be 1hr rather than 0 hr
     

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