Sprinkler Substitution for 1-hour protection.

We are designing a 2-story Type V-B cottage using the 2007 CBC and 2007 CFC.
Construction Type: 5B
Occupancy: R-3/U

(It's a 960 sf 2nd floor residence constructed over a 3-car garage below.)

The structure is within a floodplain.

We are providing the required occupancy separation between the garage and the residence above w/ 5/8" type "x" gyp. bd.

Our problem is this:
How do we provide the required 1-hour protection for the members suppoting the protected floor/ceiling assembly? (Gypsum board products are not allowed below the flood plain.)

Because we are also providing an automatic fire sprinkler system throughout, shouldn't that be an an acceptable substitute for the required 1-hr protection of the supporting members?

Footnote "e" from CBC's table 601 suggests fire sprinklers are an acceptable alternative to the 1-hour requirement but the building official won't bite.

Any suggestions?
Original Post
A couple of points....

1) CBC Section 406.1.4 states...."Garages beneath habitable rooms shall be separated from all habitable rooms above by not less than 5/8" Type "X" G.B. or equivalent."

This tells me that the ceiling of the garage need to be protected by not less than 5/8" Type "X" G.B. or equivalent....BUT does not say anything about the walls supporting the ceiling.

We assume that because the ceiling is rated, then the walls below must also be rated....but the code does not specify that. It's a requirement that appeared in the 2001 CBC.

2) When the code talks about sprinkler system substitution for one-hour fire-resistive construction as used in footnote "e" in Table 601, the sprinkler system is an approved NFPA 13 system. A sprinkler system in your cottage, R3 occupancy, will be an NFPA 13-D and would not qualify.
Supporting construction of the separation is not required.

The 2007 Codes call out only for prescriptive separation, not the use of an assembly. If a rated assembly were required, then the supporting construction would be required to be protected to the same level as the assembly it supports.
You can get away with that in housing maybe, but not with DSA projects. They often require that occupancy separations be "supported" by construction with a like rating. So a two story classroom building with a science lab on the second floor will have rated structure under the second floor walls all the way down to grade... <sigh>
Overkill, and above and beyond the code text, YES. Unfortunate reality though...

Mike E
"ADAguy Why the sigh? Its a school, Field Act mandates a higher standard. Schools are a comunity safe harbor in the event of a major disaster."

No question about the Field Act, but I somehow doubt they will be contiuning chemistry experiments or biology labs in the face of any type of disaster. If we want to use a building as a "fallout shelter" for community service post-event [remember those yellow and black signs in the old schools?], and my own opinion is that we probably should, then the whole building would likely be designed and built to a significantly higher standard. But that's not really the issue in this case.

Did you see that post from David Casey regarding this issue? Sorry wrote this before going through other notes. I think it would be a good idea, and I hope that it becomes focused and deliberate.

Sorry to hijack this thread away from the original question...
Mike E
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