Does NFPA-13 require a safety margin between system demand and available water supply on a hydraulically calculated system?
Some places require 10 psi or 10 % safety added
Yeah, this has always been a point of contention with me. NFPA 13 does not require a safety margin. However, it really should. Domestic water supply does tend to fluctuate throughout the year, and corrosion over time will also impact the hydraulics of a system. Prudent design would dictate that an official margin of safety should be added. In the government sector (DOE, DOD, etc) that margin has been officially adopted in the CFRs.
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