Fire Separation Between S-2 and R-2: Non-separated Mixed Use

[goodwork]

In constructing an open S-2 parking garage beneath R-2 apartments, what is the horizontal fire rating of the garage ceiling/apartment floor?

• Assuming non-separated mixed use
• Light gauge steel framing (apartments)
• Conventional steel frame (parking garage)
• 3 stories / 10,000 sqft per floor
• 13R Sprinkler
• Assuming Type II-B

 

[Yankee Chronicler]

You can't use a 13R system in an S-2 parking garage, so non-separated won't work.

 

[goodwork]

Right, make that NFPA 13. Can anyone point us to the path of the correct rating?

 

[walker.t]

Assuming non-separated mixed use

IBC 508.3.3 says that R-2 dwelling and sleeping units have to be separated from other occupancies per Section 420, therefore nonseparated occupancy is not an option.

IBC 420.3 (“Horizontal Separation”) says the horizontal separation between R-2 and other occupancies is to be a horizontal assembly per IBC 711 (“Floor and Roof Assemblies”). 711.2.4.3 (“Dwelling Units and Sleeping Units”) gives you two options for the rating:
1. Not less than 1 hour, there is one exception.
2. The exception applies for Type VB construction if the building is sprinklered per 903.3.1.1 (“NFPA 13 Sprinkler Systems.) If you have the specified construction type and type of sprinklers you can have a 0.50-hour rating for your horizontal separation.

13R Sprinkler

IBC 420.4 requires sprinklers in the Group R occupancy per 903.2.8. 903.2.8 requires sprinklers per 903.3. 903.3.1.2 says Group R occupancies (up to 4 stories and 60’ in height) can be sprinklered with NFPA 13R.

Right, make that NFPA 13.

As to whether you can mix NFPA 13 (for the S-2) and NFPA 13R in the same building, this post says that is possible:

Mixing NFPA 13 and NFPA 13R

Looking for an answer from fire protection engineers and fire plans examiners. A building with Type IA construction on first floor (commercial retail) with Type IIIA construction for 4 stories above (residential apartments) and a 3-hour horizontal assembly between the two construction types per...

www.thebuildingcodeforum.com

 

[Yankee Chronicler]

The only compliant way I know of to mix sprinkler systems is my making it a "podium" building. The lower portion is the parking garage, which must use a full NFPA 13 sprinkler system. The garage is separated from the residential portion above by a three-hour rated horizontal separation. The residential portion above can then use a 13R sprinkler system.