Overview of Combination Standpipe – Minimum Size

Section 7.6.2 of the 2016 edition of NFPA 14 states that the minimum size for a standpipe that is part of a combined system in a partially sprinklered building is 6-inches. 

Does this mean that a 4-inch standpipe is acceptable for a hydraulically designed combination sprinkler/standpipe system in a fully sprinklered building? 

Yes, a 4-in. minimum standpipe pipe is acceptable in fully protected buildings. Section 7.6.2 would not apply to buildings protected throughout by an automatic fire sprinkler system. Minimum standpipe pipe size is 4 in. as stated in Section 7.6.1, and all standpipes that are part of a combined system in partially sprinklered buildings must have a minimum 6 in. 

Further, Section 7.6.2.1 allows buildings protected throughout by an approved automatic sprinkler system in accordance with NFPA 13 or NFPA 13R to have a minimum standpipe size of be 4 in. for systems hydraulically designed in accordance with 7.8.1. 

The technical committee attempted to better address this in the 2016 edition by adding “where only a portion of the building has sprinkler protection” to Section 7.6.2 and clarifying the exception in Section 7.6.2.1, allowing the 4 in. pipe for systems hydraulically designed in accordance with Section 7.8.1. The substantiation for this public comment was that it reduces confusion on when a riser must be 6 in., and better correlate the relationship between Sections 7.6.2 and 7.6.3. 

In the 2019 edition of the standard, the technical committee continued to try to clarify this issue further by again making Sub-Section 7.6.2.1 a stand-alone requirement Section 7.6.3. The committee statement justifying the change was that “AHJs still don’t believe that a standpipe can be 4 in. when the building is sprinklered throughout. Since this is subset under 7.6.2.1, AHJs are not allowing the standpipe to be 4 in. even though the building is sprinklered throughout”. This change was a unanimous decision by the committee. 

The standard also allows the water supplies of combined systems in buildings protected throughout in accordance with NFPA 13 and NFPA 13R to be based on the sprinkler demand including hose stream demand or the standpipe demand, whichever is greater (Section 7.10.1.3.1.1). However, in buildings with combined systems and partial sprinkler protection, the flow rates of Section 7.10.1 must be increased by an amount equal to the sprinkler demand or 150gpm for light hazard, or by 500gpm for ordinary hazard occupancies, whichever is less (Section 7.10.1.3.2) 

Location: Canada

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