Providing Water Storage for Firefighting
The average fire sprinkler system requires seven pounds per square inch (psi) of water pressure to operate effectively. If a residential home water system doesn’t meet the psi needs of the fire sprinkler system (called fire flow), a water storage solution may be needed to obtain a building permit.
One fire sprinkler can use on average eight gallons-per-minute (GPM). Most home fire sprinkler systems accommodate two simultaneous flowing sprinklers, with a minimum need of 16 GPM to supply them with water. The size of a house, local building requirements, and the water source may require more sprinklers or be required at a higher pump rate. One or two sprinklers must flow for a minimum of 7-10 minutes, which can be provided by a well water tank or a rainwater tank when sprinklers are not supplied by a water distribution system. Fire sprinkler systems that aren’t supplied enough by a utility water source, need an on-hand water supply of at least 15% of the total required fire flow (but exact percentage is based on local authority requirements).
The National Fire Academy (NFA) developed a simple method of calculating fire flow to estimate the amount of water needed to fight fires. This method estimate is based on studying a large number of working fires and a survey of fire officers throughout the country. Learn More about the NFA
Needed fire flow = [(length x width) ÷ 3] x percent of involvement
Example: For a 30′ x 50′ building that’s 25 percent involved, the flow would be 30 x 50 = 1,500 square feet, divided by 3 = 500 x 0.25 = 125 GPM.
Additional water storage ensures that your property has water on hand for emergencies, typically with its pump system that won’t go down in case of electricity failure. This becomes even more important, if not required, based on how rural the property location is.
Rural water distribution systems that are found to be inadequate to supply 16 GPM for fire sprinklers, would probably fall short of the minimum code-required plumbing demand, and it would surely fall far short of the 1,000+ GPM needed from fire hydrants to support a fire department extinguishing a fire in a home without a sprinkler system.
To figure out the exact fire flow requirements, refer to the local Fire and Building Codes, as well as refer to the local pre-inspection requirements. If fire flow must be measured in regards to the local Fire Code, the ICC International Code Council provides a chart to show fire flow requirements based on of building construction and square footage. The ICC Construction Types that determine the fire flow, are listed in the drop-down below. The calculation uses the ICC minimum required fire-flow and flow duration for buildings.
TYPE I-A–Fire Resistive Non-combustible (Commonly found in high-rise buildings and Group I occupancies).
3 Hr. Exterior Walls*
3 Hr. Structural Frame
2 Hr. Floor/Ceiling Assembly
1 ½ Hr. Roof Protection
TYPE I-B–Fire Resistive Non-Combustible (Commonly found in mid-rise office & Group R buildings).
2 Hr. Exterior Walls*
2 Hr. Structural Frame
2 Hr. Ceiling/Floor Separation
1 Hr. Ceiling/Roof Assembly
TYPE II-A–Protected Non-Combustible (Commonly found in newer school buildings).
1 Hr. Exterior Walls
1 Hr. Structural Frame
1 Hr. Floor/Ceiling/Roof Protection
TYPE II-B–Unprotected Non-Combustible (the Most common type of non-combustible construction used in
commercial buildings).
Building constructed of non-combustible materials but these materials have no fire resistance.
TYPE III-A–Protected Combustible (Also known as “ordinary” construction with brick or block walls and a
wooden roof or floor assembly which is 1-hour fire-protected).
2 Hr. Exterior Walls*
1 Hr. Structural Frame
1 Hr. Floor/Ceiling/Roof Protection
TYPE III-B–Unprotected Combustible (Also known as “ordinary” construction; has brick or block walls with a
wooden roof or floor assembly which is not protected against fire. These buildings are frequently found in
“warehouse” districts in older cities.)
2 Hr. Exterior Walls*
No fire resistance for structural frame, floors, ceilings, or roofs.
TYPE IV–Heavy Timber (also known as “mill” construction; to qualify all wooden members must have a
minimum nominal dimension of 8 inches.)
2 Hr. Exterior Walls*
1 Hr. Structural Frame or Heavy Timber
Heavy Timber Floor/Ceiling/Roof Assemblies
TYPE V-A–Protected Wood Frame (Commonly used in the construction of newer apartment buildings; there is
no exposed wood visible.)
1 Hr. Exterior Walls
1 Hr. Structural Frame
1 Hr. Floor/Ceiling/Roof
TYPE V-B–Unprotected Wood Frame (Examples of Type V-N construction are single-family homes and
garages. They often have exposed wood so there is no fire resistance.)
The following calculation uses the ICC Fire Flow based on the above construction types of the square footage of the building. The chart below reflects the calculation as well.
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