Subcategory A and B in Construction Type



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    David Kaplan


    Nope, that's really it.  B is a lesser degree of protection than A - for example - IIB is 0 HR rated, IIA is 1 HR rated. 

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    Yingnan Bao

    Thanks David!
    I had some sort of strange illusion that A is for high-rise and B is for low to mid-rise...

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    Matthew Dirksen

    An excerpt from the 2015 International Building Code With Commentary (a Must Read, in my opinion):

    "Types I, II, III and V construction are further subdivided
    into two categories (A and B). Type A and B
    construction are not defined in the code. The designations
    simply refer to the hourly fire-resistance rating
    required for the structural elements. A Type A
    designation will have a higher fire-resistance rating
    for the structural element than a Type B designation.
    In other than Type I construction, Types A and B are
    often referred to as protected and unprotected construction,
    respectively. Please note this terminology
    does not refer to whether the building is protected by
    an installed automatic sprinkler system."

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    Yingnan Bao

    Thanks Matthew!

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