Small Project Design

BI(h)OME (by Kevin Daly Architects)

Quick Links

Who we are

AIA Small Project Design (SPD) Knowledge Community supports, celebrates, and promotes small projects by engaging designers and the public.

Expand all | Collapse all

Type V: When a fire-rated wall meets fire-rated floor, and vice versa

  • 1.  Type V: When a fire-rated wall meets fire-rated floor, and vice versa

    Posted 08-24-2020 18:20
    How do I find a set of details (preferably UL listed or ESR rated, if possible) that solve the intersection between a 1-hour rated wall and a 1-hour rated floor assembly, in Type V construction?

    I'm working on a couple of residential duplexes. In each duplex, I have two units that start out side by side on the ground level, then on the second floor, one of the units goes over part of the other unit. The plan checker is insisting that a rated wall cannot end at a rated floor (as in a T-intersection, if viewed in section), that a rated floor cannot end at a rated wall (as a T-intersection if viewed in section), and that a rated wall and rated floor cannot form an L-intersection (if viewed in section). The plan checker says the 1-hour separation wall must extend from foundation to roof. Previous similar projects were permitted, so now I am confused. Have I learned this incorrectly?

    Thanks in advance for your advice and guidance!


    ------------------------------
    Sandy Liu AIA
    Pasadena CA
    ------------------------------
    Open: Call for applications deadline November 6. Learn more and apply to join your Knowledge Community leadership!


  • 2.  RE: Type V: When a fire-rated wall meets fire-rated floor, and vice versa

    Posted 08-25-2020 17:42
    This is a tricky detail to say the least; it is one that we have to navigate often in narrow-lot, or "zero-lot-line" houses, and with duplex configurations.

    First, I would point to the Gypsum Association Manuals that offer tested, accepted assemblies for all fire and acoustic situations - it is the Bible of fire assemblies.  Here is a link: https://law.resource.org/pub/us/code/bsc.ca.gov/sibr/org.gypsum.GA-600-09.pdf  They're also available to call to review and discuss - take them up on it.  Do not recreate these, rather cut and paste them into your sets so you don't miss anything; the small aspects of the details are what will make/break the assembly and leave you in a difficult position so far as liability is concerned.

    Secondly, and most importantly, the execution of this detail in the field by the Contractor, is critical.  The sequencing of the layers is often atypical to standard construction processes; it requires trades engage at intervals which a lesser experienced crew will potentially miss.  Likewise, inspectors without experience in these assemblies may have difficulty reviewing in the field.  The result is often frustration by Contractors - that will likely be taken out on the professional as "something that cannot be built" - just beware.  You will likely want to have a pre-construction meeting to walk through these so that they are understood and anticipated.  Ensure they have read and understand the assembly in all its details and ensure them that no part can be omitted.

    Hope that helps?

    ------------------------------
    Craig Hausman AIA
    Principal
    hausman* architecture, inc
    Sacramento CA
    ------------------------------

    Open: Call for applications deadline November 6. Learn more and apply to join your Knowledge Community leadership!


  • 3.  RE: Type V: When a fire-rated wall meets fire-rated floor, and vice versa

    Posted 08-25-2020 18:17
    Craig, thank you for the link! It also reminds me to flip through my (dusty) copy of "The Gypsym Construction Handbook." I appreciate you sharing what sounds like some personal experience with the challenges of getting these details built.

    So... MUST fire rated walls extend from foundation to roof, as the plan checker claims?? It sounds unreasonable to confine spatial design in such a vertical manner.

    ------------------------------
    Sandy Liu AIA
    Pasadena CA
    ------------------------------

    Open: Call for applications deadline November 6. Learn more and apply to join your Knowledge Community leadership!


  • 4.  RE: Type V: When a fire-rated wall meets fire-rated floor, and vice versa

    Posted 08-26-2020 17:59
    HI Sandy: Here is San Jose the CIty is requiring foundation to be constructed in a crawl space where a second dwelling, (such as an ADU) is attached to an existing dwelling.  I agree, it does not make a whole lot of sense.  For instance, in a multi-family ATTIC, an attic (fire-rated 1 hour construction assembly) may pass over several dwellings and only needs a draft stop when the attic reaches a certain size.  Also there are MANY apartments here with crawl spaces through which the sewer pipe runs, picking up sewage from each unit. I hate to think of the nightmare of trying to get a crawl space installed sewer to slope correctly and having to pass through a FOUNDATION wall demising each unit!
    However, I was complaining about this to other architects, and another architect advised that I was not going to win this argument with the City.  Not helpful maybe.
    I would like to understand the code interpretation of this requirement.

    ------------------------------
    Maia Gendreau AIA
    San Jose CA
    ------------------------------

    Open: Call for applications deadline November 6. Learn more and apply to join your Knowledge Community leadership!


  • 5.  RE: Type V: When a fire-rated wall meets fire-rated floor, and vice versa

    Posted 08-25-2020 18:44
    I think the plan inspector is quoting R302.3 about two family dwellings.   "Fire resistance rated floor/ceiling and wall assemblies shall extend to and be tight against the exterior wall and wall assemblies shall extend from the foundation to the underside of the roof sheathing."

    The exception I see is R302.3.1 Supporting construction.   Where floor assemblies are required to be fire resistance rated by Section R302.2 The supporting construction of such assemblies shall have an equal or greater fire resistance rating.

    You might suggest that the wall terminating at the underside of the floor structure is "supporting construction." and if 1 hour rated does not necessarily have to extend to the roof deck above.   What additional protection for the building is achieved if the wall does extend to the roof sheathing: the two units are separated by a 1 hour barrier.

    You caused me to say What and go back and read the code.

    ------------------------------
    Peter Carlsen AIA
    Carlsen & Frank Architects
    Saint Paul MN
    ------------------------------

    Open: Call for applications deadline November 6. Learn more and apply to join your Knowledge Community leadership!


  • 6.  RE: Type V: When a fire-rated wall meets fire-rated floor, and vice versa

    Posted 09-09-2020 16:41
    I brought your question to our code committee.  The head of the Minneapolis plan review said it is one of those things that when you look...you almost wished you hadn't.  He noted:

    Duplexes can only be built under there IRC.
    Duplexes are defined in the IRC as being completely separated either horizontally or vertically.   They can not be one partially over the other.

    You have uncovered an area of the IRC that probably needs to be revised.   His final comment was: ... an architect could always present the issue of the stepped duplex under the alternative compliance path.  I think your issue needs to be brought to the attention of people working on revisions to the IRC.





    ------------------------------
    Peter Carlsen AIA
    Carlsen & Frank Architects
    Saint Paul MN
    ------------------------------

    Open: Call for applications deadline November 6. Learn more and apply to join your Knowledge Community leadership!


  • 7.  RE: Type V: When a fire-rated wall meets fire-rated floor, and vice versa

    Posted 09-09-2020 16:59
    HI Sandy:  in my experience in multifamily construction and in Single Family with attached ADU it is quite common for one part of the residence to overlap the other.  I use a 1-hour fire-rated floor assembly, either from the building code, the UL manual or the Gypsum Association manual, and a fire-rated wall assembly.  There will be solid blocking above the wall, and unfortunately, a continuous footing in the crawl space, if the wall is not landing on a slab.


    ------------------------------
    Maia Gendreau AIA
    MBA Architects
    San Jose CA
    ------------------------------

    Open: Call for applications deadline November 6. Learn more and apply to join your Knowledge Community leadership!


  • 8.  RE: Type V: When a fire-rated wall meets fire-rated floor, and vice versa

    Posted 09-11-2020 20:06
    I have run into similar situations.
    Do not forget that when you construct the 1-hour rated floor assembly that ALL supporting walls of that assembly must also be 1-hour rated.
    It would not make any sense to have a 1-hour rated floor assembly supported by 20-minute supported walls.
    Goof Luck

    David R. Cook, AIA
    Tipp City, Ohio

    ------------------------------
    David Cook AIA
    Tipp City OH
    ------------------------------

    Open: Call for applications deadline November 6. Learn more and apply to join your Knowledge Community leadership!