sprinklernotes Guest Houses and NFPA 13D “I have a single-family residence with a detached garage with living quarters. I have designed a shared antifreeze system in South Lake Tahoe. The system will share one backflow device and one riser assembly. The plan reviewer is referencing CRC 313.3.3.3 stating that I cannot have more than one dwelling on one supply. I see this as one dwelling with two structures detached. What is your opinion?”
We have reviewed the 2019 California Residential Code and NFPA 13D, Standard for the Installation of Sprinkler Systems in One- and Two-Family Dwellings and Manufactured Homes, 2019 edition as the applicable standard. Our informal interpretation is that the garage structure would be considered a separate dwelling; however, a second supply would not be required, and sprinklers would not be required to be installed in the garage. Per the 2019 California Residential Code (CRC) section 313.3.1, residential fire sprinkler systems are required to be installed in accordance with NFPA 13D or section 313.3. While the 2019 CRC requires sprinklers in detached garages, the 2019 edition of NFPA 13D explicitly states that sprinklers are not required in section 8.3.4. Since the CRC gives you the choice, if you choose to design to NFPA 13D, then sprinklers may be omitted from the garage. The two structures would be considered separate dwelling per the definition provided in the standard. 3.3.4 Dwelling. Any detached building, or any part of a townhouse structure that is separated from the remainder of the townhouse structure with fire resistance rated assemblies in accordance with local building code, that contains no more than two dwelling units intended to be used, rented, leased, let, or hired out to be occupied or that are occupied for habitation purposes. Since they are detached, the two structures would be considered separate dwellings, but this does not require a separate supply. This is scenario is addressed in section 6.2.3: 6.2.3* Where more than one dwelling unit is served by the same water supply pipe, each dwelling unit shall have an individual control valve that serves the fire sprinkler system in that dwelling unit and the owner shall have access to the valve that controls the sprinkler system in their unit. The standard only requires a separate control valve so that the other system can be isolated and that the owner has access. This is not an issue as the two structures are under the control of a single owner which has been a standard practice used by NFPA 13, Standard for the Installation of Sprinkler Systems, to allow for a single supply to feed multiple structures under control of the same owner. In my professional opinion, a single supply and control valve would suffice for this arrangement; however, provisions for guest houses are not specifically addressed in the 2019 edition of NFPA 13D, and we do not feel that the current language in the standard adequately addresses this issue. We have flagged this for further consideration in the 2025 edition of the standard as the revision cycle for the 2022 edition has closed.
