Requirements for Drains in Fire Sprinkler Systems

Drainage from a fire sprinkler system can often be overlooked as it does not directly fight the fire. However, those involved in inspections & testing of sprinkler systems know all too much about how poor drain design for a sprinkler system can negatively impact how tests are conducted, how long it takes a system to drain, and what messes building owners have to deal with.

​Here are various components for drains on a sprinkler system, and some of the common requirements that pair with them.

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Component	Notes / Description
Purpose	​Properly sized and arranged drains help minimize the amount of time a system is out of service. For pre-action and dry systems, drains also help minimize the amount of time water is prone to freezing temperatures. Some drains also help verify the water supply.  [NFPA 13 2002 §8.15.2, 2007-16 §8.16.2, 2019 16.10]
Approval / Listing	Approval / Listing: Drains are not required to be listed but must be approved.  [NFPA 13 2002 §6.1.1, 2007-10 6.7.3, 2013-16 §6.1.1.5, 6.6.3, 2019 §7.1.1.5, 16.9.1.1]
Discharge Location	Drains must discharge to the outside or to drain capable of handling drain flow. [NFPA 13 2002 §8.15.2.4.4, 2007-16 §8.16.2.4.4, 2019 §16.10.4.4] Drains cannot discharge in blind spaces under a building. [NFPA 13 2002 §8.15.2.6.4, 2007-16 §8.16.2.6.4, 2019 §16.10.6.4] Cannot direct connect to sewer and must conform to health/water dept. regulations. [NFPA 13 2002 §8.15.2.6, 2007-16 §8.16.2.6, 2019 §16.10.6]
Floor Drain Capacities	The following are approximate plumbing floor drain intake capacities, according to Standard Detail P-33 from Plumbing Engineer. In many cases, floor drains are not acceptable to handle flow from main drains, PRV discharge, or inspector's tests. 2” Floor Drain = 7 gpm             5” Floor Drain = 78 gpm 3” Floor Drain = 10 gpm           6” Floor Drain = 126 gpm 4” Floor Drain = 43 gpm          8” Floor Drain = 272 gpm
Signage	Clear permanent signage of weatherproof metal or rigid plastic is required to identify a drain valve, secured with corrosion-resistant chain or wire or other approved means. [NFPA 13 2002-13 §6.7.4.1, 2016 §6.6.4.1, 2019 §16.9.12.1] ​ ​For dry or pre-action systems with auxiliary or low-point drains, signage is required at the riser indicating quantity and location of each individual drain. [NFPA 13 2007-16 §8.16.2.5.3.7, 2019 §16.10.5.3.7]
Size of Main Drain	Serving risers and mains, size according to riser/main size. [NFPA 13 2002 Table 8.15.2.4.2, 2007-16 Table 8.16.2.4.2, 2019 Table 16.10.4.2] Riser Size                        Drain Size 1” to 2”                       ¾” or Larger 2-1/2” to 3”                 1-1/4” or Larger 4” or More                      2” or Larger ​ Serving pressure-reducing valves, sized to allow flow of greatest demand of PRV. [NFPA 13 2002 §8.15.2.4.5, 2007-16 §8.16.2.4.5, 2019 §16.10.4.5]
Size of Drain Riser	​Drain risers acting as a common riser for multiple floor control valves must be piped one-size larger than any drain connection typing into it. [NFPA 13 2002 §8.15.2.4.7, 2007-13 §8.16.2.4.7, 2016 §8.16.2.4.8, 2019 §16.10.4.8]
​Where Required	Antifreeze Pendents: Water must be drained from entire system after hydrostatic test if completed with water. [NFPA 13 2007-16 §7.6.1.3, 2019 §8.6.1.3] Antifreeze Riser/Backflow: Must be capable of draining antifreeze system. [NFPA 13 2002 §7.5, 2007-16 §7.6,  2019 §8.6] Antifreeze Remote Point: At the most remote portion of the system (with test). [NFPA 13 2007 §7.6.3.5, 2010-16 §7.6.3.6, 2019 §8.6.3.6] Exposure Protection System Riser: Except for top-fed, open systems.   [NFPA 13 2002 §7.7.4.1, 2007-13 §7.8.4.1, 2016 §7.7.4.1, 2019 §8.7.4.1] Fire Department Connection: Pipe between check valve and outside connection in areas subject to freezing must have an automatic drain valve, that is approved and in an area that permits inspection & testing. Where trapped, auxiliary drain is required. [NFPA 13 2002 §8.16.2.6, 2007-16 §8.17.2.6, 2019 §16.12.7] Floor Control Assemblies: At floor control valve assembly for buildings over two stories in height, except on top-level if sprinklers are fed from level below. [NFPA 13 2013 §8.16.1.5.1, 2016 §8.2.4.1, 2019 §16.9.11.1] System Valve (Main Drain): Each system must be capable of being drained. [NFPA 13 2002 §8.15.2.1, 2007-16 §8.16.2.1, 2019 §16.10.1] Trapped Pipe (Wet or Non-Freezing Pre-Action): Where trapped section of pipe: - contains less than 5 gallons, auxiliary drain, single pendent sprinklers capable of draining section, or flexible coupling must be provided, - contains 5 gallons or more, minimum ¾” auxiliary drain must be provided - contains 50 gallons or more, minimum 1” auxiliary drain must be provided. [NFPA 13 2002 §8.15.2.5.2, 2007-16 §8.16.2.5.2,  2019 §16.10.5.2] Trapped Pipe (Dry or Pre-Action): Where system is trapped: - containing less than 5 gallons, min. ½” auxiliary drain valve with plug or nipple/cap - tie-in drains required for multiple adjacent trapped branch pipes. ​[NFPA 13 2002 §8.15.2.5.3, 2007-16 §8.16.2.5.3, 2019 §16.10.5.3]