ryan81
Member
Hello All -
Code Version: 2021 IBC.
See attachments.
I am working on a project where I need to design a 2-hour rated horizontal assembly between the main level and second floor of an existing building for purposes of allowing a change in occupancies (M on the main level and potentially a single R-2 dwelling unit on the second level). The building is not protected by an automatic sprinkler system, however it should be noted that the jurisdiction where this project is located has adopted an amendment allowing a single dwelling unit in a building with A, B, or M occupancies without an automatic sprinkler system.
The original building was constructed as a single-story structure out of 8-inch CMU exterior walls and a steel roof structure. At some point, the roof was removed, a course of CMU was added to the tops of the exterior walls around the perimeter, and a second floor was constructed out of 3/4" plywood over parallel chord wood trusses and wood-framed 2nd floor exterior walls topped by a wood truss roof. The wood floor trusses span from exterior wall to exterior wall and are not supported by the original steel roof structure, some of which remains in-place.
Where existing steel structure does not exist, I am planning on employing UL Design L577. Where the existing steel structure remains, there is insufficient space between the top of the existing steel and the bottom of the wood trusses to allow the installation of L577, so I need to find another solution. So far I have not found a tested assembly for plywood on parallel chord trusses with a suspended gypsum board ceiling to get the ceiling membrane below the existing steel and mechanical ductwork. At first I thought I could use the calculated fire-resistance method in the IBC, but 722.6.1.1 limits the calculation method to 1-hour for wood floors. No luck finding an assembly under the prescriptive approach either.
I'm guessing I will need an Engineering judgement from a fire protection engineer, but thought I'd put this problem out in front of you all in case you've been up against a similar scenario and have found a solution.
Your thoughts/help are truly appreciated.
Thanks!
Code Version: 2021 IBC.
See attachments.
I am working on a project where I need to design a 2-hour rated horizontal assembly between the main level and second floor of an existing building for purposes of allowing a change in occupancies (M on the main level and potentially a single R-2 dwelling unit on the second level). The building is not protected by an automatic sprinkler system, however it should be noted that the jurisdiction where this project is located has adopted an amendment allowing a single dwelling unit in a building with A, B, or M occupancies without an automatic sprinkler system.
The original building was constructed as a single-story structure out of 8-inch CMU exterior walls and a steel roof structure. At some point, the roof was removed, a course of CMU was added to the tops of the exterior walls around the perimeter, and a second floor was constructed out of 3/4" plywood over parallel chord wood trusses and wood-framed 2nd floor exterior walls topped by a wood truss roof. The wood floor trusses span from exterior wall to exterior wall and are not supported by the original steel roof structure, some of which remains in-place.
Where existing steel structure does not exist, I am planning on employing UL Design L577. Where the existing steel structure remains, there is insufficient space between the top of the existing steel and the bottom of the wood trusses to allow the installation of L577, so I need to find another solution. So far I have not found a tested assembly for plywood on parallel chord trusses with a suspended gypsum board ceiling to get the ceiling membrane below the existing steel and mechanical ductwork. At first I thought I could use the calculated fire-resistance method in the IBC, but 722.6.1.1 limits the calculation method to 1-hour for wood floors. No luck finding an assembly under the prescriptive approach either.
I'm guessing I will need an Engineering judgement from a fire protection engineer, but thought I'd put this problem out in front of you all in case you've been up against a similar scenario and have found a solution.
Your thoughts/help are truly appreciated.
Thanks!