17.1 Residential Fire Sprinkler Systems (IRC Section P2904)

Why this is on a plumber's exam

C.R.S. 12-155-103(8)(a) includes in the definition of plumbing "all multipurpose residential fire sprinkler systems in one- and two-family dwellings and townhouses that are part of the potable water supply." A multipurpose system is plumbing, installed by plumbers, inspected by plumbing inspectors. The PSI blueprint reflects that with 2 scored items on the Journeyworker exam and 4 items on the Residential Plumber and Master exams.

The governing text is IRC Section P2904, part of IRC Chapter 29, which Colorado adopts through Board Rule 1.2(A)(2).

Two system types — IRC P2904.1

The design and installation of residential automatic sprinkler systems shall be in accordance with NFPA 13D or Section P2904, which shall be considered to be equivalent to NFPA 13D. Partial residential sprinkler systems shall be permitted to be installed only in buildings not required to be equipped with a residential sprinkler system. Section P2904 shall apply to stand-alone and multipurpose wet-pipe sprinkler systems that do not include the use of antifreeze.

A backflow preventer shall not be required to separate a sprinkler system from the water distribution system, provided all four of the following are met:

1. The system complies with NFPA 13D or Section P2904.
2. The piping material complies with Section P2906.
3. The system does not contain antifreeze.
4. The system does not have a fire department connection.

That aligns with IPC 608.17.4 Exception 1: where systems are installed as a portion of the water distribution system and are not provided with a fire department connection, isolation of the water supply system is not required. Add antifreeze or a fire department connection and backflow protection returns — IPC 608.17.4.1 then requires a reduced pressure principle assembly.

Where sprinklers are required — IRC P2904.1.1

Sprinklers shall be installed to protect all areas of a dwelling unit.

Four exceptions:

1. Attics, crawl spaces and normally unoccupied concealed spaces that do not contain fuel-fired appliances. Where such a space does contain fuel-fired equipment, a sprinkler shall be installed above the equipment, but sprinklers are not required in the remainder of the space.
2. Clothes closets, linen closets and pantries not exceeding 24 square feet in area, with the smallest dimension not greater than 3 feet, having wall and ceiling surfaces of gypsum board.
3. Bathrooms not more than 55 square feet in area.
4. Garages; carports; exterior porches; unheated entry areas, such as mud rooms, that are adjacent to an exterior door; and similar areas.

Three numbers to hold: 24 square feet and 3 feet for closets and pantries, and 55 square feet for bathrooms.

Sprinklers — IRC P2904.2

Sprinklers shall be new listed residential sprinklers and shall be installed in accordance with the sprinkler manufacturer's instructions.

New is literal. P2904.2.6 prohibits painting, caulking or modifying sprinklers, and requires sprinklers that have been painted, caulked, modified or damaged to be replaced with new sprinklers.

Temperature ratings — P2904.2.1 and P2904.2.2

Intermediate temperature sprinklers are required where installed:

1. Directly under skylights, where exposed to direct sunlight.
2. In attics.
3. In concealed spaces located directly beneath a roof.
4. Within the distance to a heat source specified in Table P2904.2.2.

Table P2904.2.2 ranges, measured in a straight line from the nearest edge of the heat source to the nearest edge of the sprinkler:

Footnote a: sprinklers shall not be located at distances less than the minimum table distance unless the sprinkler listing allows a lesser distance. So the table does double duty: below the minimum, no sprinkler at all; within the range, an intermediate-temperature sprinkler; beyond the range, an ordinary sprinkler.

Freezing areas — P2904.2.3

Piping shall be protected from freezing as required by IRC P2603.5, or by using:

1. A dry-pipe automatic sprinkler system listed for residential occupancy applications, or
2. Dry-sidewall or dry-pendent sprinklers extending from a nonfreezing area into a freezing area.

In Colorado, an unheated garage or an attic above an unconditioned space makes this a routine design question.

Coverage and obstructions — P2904.2.4

The area of coverage of a single sprinkler shall not exceed 400 square feet, and shall be based on the sprinkler listing and the sprinkler manufacturer's installation instructions.

P2904.2.4.2 Obstructions: sprinkler discharge shall not be blocked by obstructions unless additional sprinklers protect the obstructed area. No additional sprinklers are required where separation complies with Figure P2904.2.4.2 or the manufacturer's instructions where they permit a lesser distance.

In both cases, additional sprinklers shall be installed.

P2904.2.5: on systems assembled with solvent cement, the cementing of threaded adapter fittings shall be completed and the adapters verified as clear of excess cement before sprinklers are installed. Cement squeezed into a sprinkler orifice disables it silently.

Piping — IRC P2904.3

Sprinkler piping shall be supported in accordance with requirements for cold water distribution piping and shall comply with the requirements for cold water distribution piping. For multipurpose piping systems, the sprinkler piping shall connect to and be a part of the cold water distribution piping system.

P2904.3.1: nonmetallic pipe and tubing such as CPVC, PEX and PE-RT shall be listed for use in residential fire sprinkler systems — ordinary potable-rated CPVC is not automatically acceptable.

P2904.3.1.1 Nonmetallic pipe protection: nonmetallic systems shall be protected from exposure to the living space by not less than 3/8-inch gypsum wallboard, 1/2-inch plywood, or other material having a 15-minute fire rating. Two exceptions: areas that do not require sprinkler protection under P2904.1.1, and where exposed piping is permitted by the pipe listing.

P2904.3.2 Shutoff valves prohibited:

With the exception of shutoff valves for the entire water distribution system or a single master control valve for the automatic sprinkler system that is locked in the open position, valves shall not be installed in any location where the valve would isolate piping serving one or more sprinklers.

This is the rule that most often collides with plumbing habit. You may not put a stop on a branch that also feeds a sprinkler.

P2904.3.3 Single dwelling limit: piping beyond the service valve at the beginning of the water distribution system shall not serve more than one dwelling.

P2904.3.4 Drain: a means to drain the sprinkler system shall be provided on the system side of the water distribution shutoff valve.

Determining design flow — IRC P2904.4

P2904.4.1: the minimum required flow for each sprinkler comes from the manufacturer's published data for the specific model, based on the area of coverage, the ceiling configuration, the temperature rating, and any additional manufacturer conditions.

P2904.4.2 System design flow rate:

1. A room with one sprinkler: the flow required for that sprinkler.
2. A room with two or more sprinklers: the highest required flow rate in that room multiplied by 2.
3. Where the manufacturer specifies different criteria for non-smooth, non-flat or non-horizontal ceilings, follow the manufacturer's instructions.
4. The design flow rate for the system is the flow required by the room with the largest flow rate.
5. It is permissible to reduce the design flow by subdividing a space into two or more rooms, each bounded by walls and a ceiling, where openings in walls have a lintel not less than 8 inches in depth forming a solid barrier between the ceiling and the top of the opening.

Two sprinklers, never more. No matter how many sprinklers a room contains, the design case is two operating, and the number used is twice the single highest flow.

Worked design flow

A house has a great room with five sprinklers (highest published flow 16 gpm), a bedroom with one sprinkler (13 gpm) and a kitchen with two sprinklers (highest 14 gpm).

System design flow = 32 gpm, the largest room requirement.

Water supply — IRC P2904.5

The water supply shall provide not less than the required design flow rate at a pressure not less than that used to comply with Section P2904.6.

P2904.5.1: where the supply is from a tank system, a private well system or a combination, the available supply is based on the minimum pressure control setting for the pump.

P2904.5.2 Required capacity — the duration the supply must sustain the design flow:

Where a well, a tank or a combination is used, any combination of well capacity and tank storage may meet the requirement.

Worked storage

The 32 gpm system above serves a two-story house on a well.

• Required duration: 10 minutes (two or more stories).
• Required volume: 32 gpm x 10 min = 320 gallons available at the design flow and pressure.

Had the house been one story at 1,800 square feet: 32 x 7 = 224 gallons.

Pipe sizing — IRC P2904.6

The piping to sprinklers shall be sized for the flow required by P2904.4.2. The flow required to supply the plumbing fixtures shall not be required to be added to the sprinkler design flow.

That sentence matters in a multipurpose system: you do not add domestic demand to sprinkler demand. The design case is a fire, during which fixture use is not assumed.

P2904.6.1 Method of sizing:

• The prescriptive method in P2904.6.2, or hydraulic calculation per NFPA 13D.
• Minimum pipe size from the water supply source to any sprinkler: 3/4 inch nominal.
• Threaded adapter fittings where sprinklers attach: not less than 1/2 inch nominal.

P2904.6.2 sizes pipe by determining the available pressure to offset friction loss, using tabulated losses:

Both service and meter tables carry the same footnote: add 5 gpm to the flow rate required by P2904.4.2 where the water service pipe supplies more than one dwelling.

Colorado context