sprinklernotes
Standpipe Branch Line Sizing
The following information was provided: The local jurisdiction requires Class I
standpipes in shell warehouses. A tenant leased one half and is constructing a
fire-rated demising wall. By chance, there was already a hose connection at the
column line of the new demising wall; however, the other side does not have
one. We would like to tee off the existing
2-1/2-in. supplying existing hose connection and pass-through wall to have
coverage on the other side of the new wall.
You asked the following question: Due to the presence of the new rated firewall
with no doors or openings, could both hose valves be supplied by the same
2-1/2-in. drop?
In response to your question(s), we have reviewed NFPA 14, Standard for the
Installation of Standpipe and Hose Systems, 2016 edition.
Our informal interpretation: The two hose valves cannot be fed from the same
2-1/2-in. drop.
NFPA 14 requires that standpipes have a minimum size of 4 in. per section 7.6.
The only piping permitted to be less than 4 in. are branch lines which can be
sized based on hydraulic calculations but no smaller than 2-1/2 in. In this
case, the pipe feeding two hose valves would not meet the definition of a
branch line:
3.3.2 Branch Line. A piping system, generally in a horizontal plane, connecting
not more than one hose connection with a standpipe.
Because two hose valves are connected, the definition of a branch line does not
apply, and the pipe would need to be sized based on the minimum sizes of
standpipes (see 3.3.16). The addition of the fire wall is not applicable as
NFPA 14 design is not dependent on the construction separation in this case.
Since it is a single standpipe system fed from a common fire department
connection (FDC), all piping has to be sized accordingly.
