I've found it difficult to come up with concrete answers in NFPA with regard to 1 &2 Family Dwellings and attached garages. Chapter 24 is all but silent on attached garages (CO section speaks to it). Are they to be treated as incidental storage or a separated storage occupancies? Over and over we see 20 min doors being specced between dwellings and garages, but that indicates a 1/2 hr. fire barrier, not a 2 hr., and not no requirement? I understand the IRC addresses this (I'm not a user of IBC/IRC), but it seems to be lacking clarity in NFPA 101?
Excerpts from 2015 NFPA 101:
3.3.190.13* Residential Occupancy. An occupancy that provides sleeping accommodations for purposes other than health care or detention and correctional. (SAF-RES)
24.1.3.1 Multiple occupancies shall be in accordance with 6.1.14.
6.1.14.1.3* Where incidental to another occupancy, areas used as follows shall be permitted to be considered part of the predominant occupancy and shall be subject to the provisions of the Code that apply to the predominant occupancy:
(1) Mercantile, business, industrial, or storage use
(2)*Nonresidential use with an occupant load fewer than that established by Section 6.1 for the occupancy threshold
42.8.1.4 Classification of Occupancy. Incidental vehicle parking in another occupancy shall not be the basis for overall occupancy classification.
To me, when it was incidental vehicle parking in accordance with Section 42.8.1.4, it would be safe to not classify them as multiple occupancies and to use Chapter 24 throughout the building based on the above code citations.
For life safety purposes no protection from hazards in Chapter 24 when it it protected by an automatic sprinkler system. This could change with electric cars- have you seen some of the battery fires - very violent to the point of being explosive. In my own resident's design, I was very reluctant to have any parking of vehicles in or communicating with my residence.
Milt