What is the Fire Rating for a low roof?

[kas]

Existing 3 story 12 inch thick brick bearing wall, wood framed- mixed use - 2 floor residential over commercial space under going change of occupancy Mercantile to Business.

Under IEBC, change to lower hazard, the existing rating of exterior walls is ok.

Low roof rating?

The first floor goes from side to side property lines. 2nd and 3rd have inset 5x10 courts to give light to windows.
Would like to run grease and make up air duct work from 1st floor thru the roof/floor of one of those courts up side of building to new equipment on roof.

Existing parapet is 12 inches high.

How to figure out the fire rating of that roof?

Thanks

 

[RLGA]

What is building area of the 1st story, 2nd story, and 3rd story?

 

[steveray]

So.....The exterior walls are party walls? What are their fire ratings? 10' back 1hour rating rings a bell (for stepped buildings), but I would have to spend some time looking....Ch. 7 is your friend...

 

[kas]

rlga-

39 ft tall
ground floor - 1746 sf
2nd/3rd 1631 sf each

steveray

they are zero lot line walls.

the interplay between the IBC and IEBC and required ratings is tricky.

IEBC-under chapter 10, change of occupancy- bc lesser hazard, ext wall fire resistance is accepted.By adding the duct penetrations, I am not changing the existing wall/roof.

IBC-
existing walls are 12 inch brick- assume min 2 hr

if consider the existing construction 5B- meet area and height but not story.
3B- meet both-

roof as 0hr either 3b or 5b
walls need to be 1hr bc of distance from property line

i am being told that bc parapet is less than 30 inches, the low roof needs to be 1hr rather than 0 hr