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Fire-rated exterior walls using FRTW framing as acceptable IBC substitute for non-combustible stl studs or masonry

  • 1.  Fire-rated exterior walls using FRTW framing as acceptable IBC substitute for non-combustible stl studs or masonry

    Posted 08-26-2020 18:30

    Has anyone out there had experience designing 2-hr rated load-bearing exterior walls using fire-resistive treated wood (FRTW), rather than masonry or stl studs (mpore typical

    non-combustible materials) ?  I understand the IBC allows this as a substitute for non-combustible framing materials. I'm being asked to detail with this for a self-performed owner-builder project because the owner-builder (not a commercial contractor - actually a small-scale developer-property manager) is more comfortable working with wood than stl or masonry.  Local code official is allowing it per the IBC exception, but I'm just wondering if there are any tips out there from your prior experience with it.  I've never happened to have the occasion to use if before.  We're required to make these walls 2-hr-rated because they'll be built right on the property lines of a narrow urban lot, and windows in these walls will also be required to be 2-hr (actually 90 min rated) labeled and will have to be non-operable, even though the residential spaces in the building will be sprinklered per NFPA 13R standard for residential.  Thanks for any advice or suggestions.



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    Eugene Aleci AIA
    Architect / President
    Community Heritage Partners
    Lancaster PA
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  • 2.  RE: Fire-rated exterior walls using FRTW framing as acceptable IBC substitute for non-combustible stl studs or masonry

    Posted 08-28-2020 09:34

    Be careful.  The 2 hour rated special Type 3 assembly is not a firewall, but a fire rated assembly.  It will require special detailing for any framing that bears on the wall.  Various manufacturers have come up with special hangers that can be complicated to install.  There are also requirements for floor framing and sub floor material adjacent to the wall construction.  Exterior finishes, membranes and insulation need to be noncombustible.  Consider future access, maintenance and durability.

     

    There are plenty of references online.  Check for how they apply to your jurisdiction and the version of the Code you are using.:

     

    https://www.woodworks.org/wp-content/uploads/17NW02-STRAND-Exterior-Walls-in-Type-III-WSF-170425.pdf

     

    Chris Semmelink RA LEED AP

     

    Sent from Mail for Windows 10

     




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  • 3.  RE: Fire-rated exterior walls using FRTW framing as acceptable IBC substitute for non-combustible stl studs or masonry

    Posted 08-31-2020 18:31
    In the Twin Cities the use of FRTW studs in a two hour load bearing exterior wall is quite common for new 5 story apartment buildings.  Top bearing open wood trusses are used with the space better the trusses blocked solid across the plates.  Building officials do not allow the trusses to bear on or penetrate stair enclosures or elevator towers. Thats where the special hangers come into play.    Loads at the bottom of the walls make for a lot of wall types with different plates and stud distributions to accommodate the weight.   If you get that high make sure your structural engineer is backing you up.

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    Peter Carlsen AIA
    Carlsen & Frank Architects
    Saint Paul MN
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