Plaster ceiling fire rating.

[UCinCAT]

I am working on a renovation of an existing (5) story building
original use was B occupancy on each floor.

First floor (street level) will remain B use.
Floors two-five will change from B to R-2.

NFPA13 sprinkler system is present on all floors and will be re-worked for the existing B occupancy and the new R-2 occupancies.

2017 Ohio Building Code.
Chapter 4 section 430.3 applies.
Horizontal assemblies separating "R" & "B" = 1hour (sprinkler) Table 508.4
Horizontal assemblies separating dwelling units and sleeping units = 1/2 hour with sprinkler [OBC 711.2.4.3 "EXCEPTION"]

My question is related to the existing plaster ceiling of the first floor "B" occupancy.
The plaster ceiling was installed circa 1925 and appears to be about 1-inch thick (lathe to finish coat).
Can i use this plaster ceiling assembly as the 1-hour separation required by Table 508.4?
The plaster ceiling needs to be repaired due to prior modifications to the space over time. The plaster ceiling is suspended from rough sawn wood joist (3x14 @ 12 o.c.) which support a wood floor assembly above).
I didn't see a close approximation in the tables found in OBC 721.
Maybe it's there but i missed it, or misread the table.

How do i confirm the fire rating of the plaster ceiling in question - if one exists?

 

[RLGA]

Since Ohio did not adopt the IEBC, you do not have Resource A which is included in that code. Resource A is the "Guidelines on Fire Ratings of Archaic Materials and Assemblies." Resource A is not adoptable, but it can be used as a justification for fire-resistive construction in existing buildings. It was originally published as a separate document but was incorporated into the IEBC when the IEBC was published in 2003. Including Resource A in the IEBC gives Resource A a level of legitimacy within the building regulation community.

Section III of Resource A covers floor/ceiling assemblies, and many include plaster as a ceiling material. I suggest looking there first to see if one of the assemblies provided matches your existing construction.

On another note, I do not see Section 430.3 in the Ohio Building Code. Also, you only need to separate occupancies per Table 508.4 if you use the separated occupancies method per Section 508.4. Otherwise, all you need are dwelling unit separations, which are less restrictive than occupancy separations (i.e., they do not require supporting construction to be of equal or greater fire-resistive construction).

 

[UCinCAT]

Since Ohio did not adopt the IEBC, you do not have Resource A which is included in that code. Resource A is the "Guidelines on Fire Ratings of Archaic Materials and Assemblies." Resource A is not adoptable, but it can be used as a justification for fire-resistive construction in existing buildings. It was originally published as a separate document but was incorporated into the IEBC when the IEBC was published in 2003. Including Resource A in the IEBC gives Resource A a level of legitimacy within the building regulation community.

Section III of Resource A covers floor/ceiling assemblies, and many include plaster as a ceiling material. I suggest looking there first to see if one of the assemblies provided matches your existing construction.

On another note, I do not see Section 430.3 in the Ohio Building Code. Also, you only need to separate occupancies per Table 508.4 if you use the separated occupancies method per Section 508.4. Otherwise, all you need are dwelling unit separations, which are less restrictive than occupancy separations (i.e., they do not require supporting construction to be of equal or greater fire-resistive construction).

Thanks so much for your reply!

it appears OBC 3401.3.5 permits the use of Resource A, despite not adopting the IEBC. So I'll start there.

I had a typo in my initial post. OBC 420.3 was intended instead of 430.3.
"Floor assemblies separating dwelling units in the same buildings, floor assemblies separating sleeping units in the same building and floor assemblies separating dwelling or sleeping units from other occupancies contiguous to them in the same building shall be constructed as horizontal assemblies in accordance with Section 711."
I read this as a rated separation is needed between B & R-2.

I think I need to use the separated occupancy method for this project , right?

• Type 3B
• (5) story structure (wood joist floor assembly typical, masonry bearing walls and exterior/perimeter
• full level below grade
• Use groups S-1, B, & R-2
• sprinklers per NFPA13 - all floors
• S-1 below grade (MEP equipment and r-2 tenant storage.)
• B at first floor (street level
• R-2 at floors 2 thru 5.

Either B or S-1 is the most restrictive occupancy compared to R-2
s-1 limited to 3 stories, B limited to 4.
existing structure is 5 stories.

I'm still a bit fuzzy on how/when to apply separated/non-separated methodologies. I think I need to re-read your book.

 

[RLGA]

As a Type IIIB building, the second item in the Exception to Section 711.2.3 would apply if not using the separated occupancies method. If using the separated occupancies method, the separation would only need to be between the second and third stories, since that is where the occupancies are different--the remaining separations between stories only need to be dwelling unit separations.

Although Type IIIB construction permits five stories for Group R-2, you must also consider allowable area. Type IIIB construction permits 48,000 sq. ft. per story up to three stories, which means you have a total allowable area of 144,000 sq. ft. for all five stories without frontage increase. If you can maximize the frontage increase, your maximum total allowable area will be 180,000 sq. ft. If your building is under 144,000 sq. ft. total, then you can use the nonseparated occupancies method for sure. If it is more than 144,000 sq. ft., then it depends on the actual area and the increase you can get for frontage.

 

[UCinCAT]

Ugh...Now I'm doubting my initial code evaluation for this project. (Newbie at this)

Floor area is not an issue here.

Actual Floor Areas (GSF)
Basement: (S-1) (5,062)
Level 01 (B): 5,228
Level 02: (R-2) 5,098
Level 03: (R-2) 4,449
Level 04: (R-2) 3,319
Level 05: (R-2) 3,319
Total 21,413

I guess I'm having trouble understanding the impact the height limitation has on a project with a non-separated occupancy scenario.
The existing building is (5) stories & approximately 75-ft above grade plane.
S-1 has a height limitation of 3 stories
B has a height limitation of 4 stories.
R-2 has a height limitation of 5 stories.

Am i not limited to 3 stories for the project without separating?
or is it just related to each specific use: i.e. S-1 cannot occupy more than 3 stories within the existing (5) story structure, B cannot occupy more than 4 stories...

 

[RLGA]

Ugh...Now I'm doubting my initial code evaluation for this project. (Newbie at this)

Floor area is not an issue here.

Actual Floor Areas (GSF)
Basement: (S-1) (5,062)
Level 01 (B): 5,228
Level 02: (R-2) 5,098
Level 03: (R-2) 4,449
Level 04: (R-2) 3,319
Level 05: (R-2) 3,319
Total 21,413

I guess I'm having trouble understanding the impact the height limitation has on a project with a non-separated occupancy scenario.
The existing building is (5) stories & approximately 75-ft above grade plane.
S-1 has a height limitation of 3 stories
B has a height limitation of 4 stories.
R-2 has a height limitation of 5 stories.

Am i not limited to 3 stories for the project without separating?
or is it just related to each specific use: i.e. S-1 cannot occupy more than 3 stories within the existing (5) story structure, B cannot occupy more than 4 stories...

I do not do a lot of Type III construction, so I did not realize that a Group B height would be more restrictive than a Group R-2 height, plus you did not mention the Group S-1 in your original post.

Yes, an occupancy separation will be required between the 1st and 2nd stories to separate the Group B occupancy from the Group R-2 occupancy. No separation is required between the Group S-1 occupancy and the Group B occupancy. The remaining stories (3, 4, and 5) will only need dwelling unit separations at the floor levels.

 

[UCinCAT]

I do not do a lot of Type III construction, so I did not realize that a Group B height would be more restrictive than a Group R-2 height, plus you did not mention the Group S-1 in your original post.

Yes, an occupancy separation will be required between the 1st and 2nd stories to separate the Group B occupancy from the Group R-2 occupancy. No separation is required between the Group S-1 occupancy and the Group B occupancy. The remaining stories (3, 4, and 5) will only need dwelling unit separations at the floor levels.

Thank you so much for your input. It appears i'm on the right track after all. now i just need to circle back to the existing plaster ceiling and whether or not it can be considered for the 1-hour separation between the first and second floor.