Can I analyze this building as VB non-separated occupancies?

[Robert]

This has probably been discussed before but am unsure how to find it. I am analyzing a 3 story building as a non-separated...ground floor B occupancy, with 2 floors directly above as R-3 occupancy. Per CBC section 508.3, the allowable height (and area) of the building or portion thereof, is based on the most restrictive occupancy (in this case B). Table 504.4 allows 2 stories for B occupancy type VB (non sprinklered). If the building is 3 stories (which exceeds the B maximum of 2 stories), but the B portion of the building is only 1 story, would this be allowed? Is this what they mean by the portion thereof? Thank you.

 

[RLGA]

The Group B must be sprinklered per IBC Section 903.2.8, which requires buildings with a Group R fire area be sprinklered throughout. If using an NFPA 13 system, then there is no problem, since it will allow a 3-story Group B. If using an NFPA 13R or 13D systems, then the nonsprinklered values for Group B must be used, which I’m assuming is the reason you mentioned a nonsprinklered Group B.

If using the nonseparated method, then the building height is limited to the most restrictive occupancy, which would be the Group B. Thus, you will need to have a 1-hour horizontal assembly separating the Group B portion from the Group R-3 at either the 2nd or 3rd story. Since you are required to separate the dwelling units from other portions of the building per Section 420 with at least a 1/2-hour horizontal assembly, you might as well make it a 1-hour horizontal assembly and use it as an occupancy separation and use the separated occupancies method.

 

[steveray]

Nailed it....

 

[classicT]

Question answered in one post. Well done @RLGA

 

[Robert]

Thank you. Just to complicate things, this is an existing unsprinklered building. The B occupancy is on the main floor (with 6' basement below) and the R-3 is above. What I am doing is digging out the basement and moving the B into that space (basically moving it one story down) and the 2 floors above continue as a single family residence. Rather then lifting the building beyond height limit, I'm digging down to take advantage of the unusable basement. That said, will this still require sprinklers? ( there is no new square footage in the B occupancy....it is just getting relocated).

 

[steveray]

Sprinkler requirements are typically “throughout the building or fire area” so you would be sprinklering the occupancy in the basement as well. And basements have their own requirements for sprinkler protection at times so watch for that...

 

[Robert]

Thanks Steveray...agreed. I guess my question is, will moving the B occupancy from one floor to the next trigger sprinklers, when none existed before.

 

[steveray]

I think I might have it now. The R is existing but you are expanding it to where the B is and the B goes to the basement?

 

[Robert]

Exactly.

 

[steveray]

As it is a new basement occupancy I would look at 903.2.11ish for basement sprinkler requirements...

 

[my250r11]

New work, install sprinklers.

 

[Robert]

Great thanks for the replies.