Up until the mid-1970s, sprinkler pipe was predominantly Schedule 40 black steel pipe.

Then an upstart company named Allied Tube and Conduit decided to shake up the piping business. At the time, Allied only produced electrical conduit and fence pipe. The owner, looking to expand his business, figured the same pipe used for fences could be used for sprinkler systems. The pipe was strong and durable, just thinner than the standard Schedule 40 pipe. Since the water just sat there waiting for a fire, why not use a thinner wall material? This started the long debate over what quality is really required for a sprinkler piping system.


Important Changes

The initial change to NFPA 13 was the introduction of Schedule 30 pipe. Following this approval, ASTM A135 was added as a referenced standard. A135 is for Schedule 10 steel pipe.

After continued discussion of pipe thickness and pipe material, the NFPA 13 Committee added a provision to the standard that allows any material that a testing laboratory certifies for sprinkler systems. The result was thinner steel pipe, less than the equivalent of Schedule 10.

After allowing thinner wall steel pipe, the question became, “What thickness can be threaded or cut-grooved to join the piping material?” NFPA 13 maintains that cut grooves or threading of steel pipe is only permitted for Schedule 40 and heavier pipe for sizes less than 8-inch, and Schedule 30 for sizes 8-inch and larger. There is an exception to this requirement for pipe that is specifically listed for threading with a thinner wall thickness. This follows the trend for relying on third-party certifying agencies to determine the quality of the piping material.

Steel pipe with threaded fittings are used for a dry pipe system in an attic.

A rolled groove is only permitted for steel pipe that is Schedule 10 or heavier in wall thickness. Other mechanical joining methods must be listed by a third-party testing agency. The limitation of the fittings is based on the manufacturer’s installation instructions.

Of course, welding of steel pipe has always been permitted.

It should be noted that galvanized pipe also is permitted. Furthermore, galvanized steel and black steel pipe and fittings can be intermingled. While the installation may look strange, there is no prohibition to such an installation.


C Factor

During the debate over wall thickness, the steel pipe industry completed a study that showed that the C factor for steel pipe was inappropriately assigned a value of C=100. The study showed that, even with aging and changes to the interior wall, steel pipe should be assigned a C factor of 140. The industry initiated a campaign of C=140. The NFPA Committee did not completely accept the recommendations of the industry. Rather, they increased the C factor to 120. That remains the C factor for steel pipe in the latest edition of NFPA 13. The other piping materials-copper, CPVC, and PEX-all have a C factor of 150.


Copper Tubing

During the period of changes to the steel pipe requirements, the copper industry launched an effort to increase the amount of copper tubing used for sprinkler installations. Type K, L or M copper tubing is permitted for any sprinkler installation.

Confusion resulted with copper tubing as to which joining method was acceptable. Initially, it was assumed that copper tubing would have to be joined by brazed joints. This was based on the belief that soldered joints would come apart under a fire condition. Brazed joints can be used on any sprinkler system for any hazard, both wet and dry.

After further evaluation, solder joints were permitted for certain systems. The current requirements allow for soldered joints for any wet piping system that is light hazard where ordinary or intermediate temperature sprinklers are used. Soldered joints also are permitted for wet piping systems in light and ordinary hazards where the piping is not exposed.

Soldered joints are never permitted for dry pipe systems. The testing to establish acceptability for dry pipe systems requires the pipe and fittings to be exposed to a heptane fire for 75 seconds before water is introduced into the piping system. In that period of time, the solder would melt out of the joint and result in a separation of the piping system.

Most recently, copper press-connect fittings were listed for all copper sprinkler systems. The fittings were listed for both wet and dry piping systems. This listing does not apply to all press connection fittings. Each fitting manufacturer must have their fittings tested. The fitting manufacturer can provide the listing information. This information also is available on the third-party testing agency’s Web site.

When using a press connection fitting system, the copper tubing is permitted to be exposed. There is no requirement for a barrier between the pipe and the area being protected by the sprinkler system. The press connection fitting system has a greater application in sprinkler systems than solder joints.

A high-rise residential building has the sprinkler system piped in BlazeMaster® CPVC pipe.



CPVC was one of the first plastic pipes approved for sprinkler systems. The CPVC piping industry has further identified the piping approved for sprinkler systems as BlazeMaster® CPVC pipe. BlazeMaster conforms to ASTM F442. This is the standard that is listed in NFPA 13.

BlazeMaster is orange in color. The outside diameter of the pipe is similar to steel pipe. As a result, there is a larger interior diameter, allowing a greater flow of water than copper tubing or CPVC used in plumbing systems.

BlazeMaster is joined with one-step solvent cement that is red in color. BlazeMaster can be joined to other types of CPVC, including FlowGuard Gold® and Corzan®. When converting BlazeMaster to other types of CPVC, the solvent cement must be the one-step solvent cement that is red in color. For the joining of Flowguard Gold or Corzan, the one-step solvent cement that is yellow in color can be used.

BlazeMaster CPVC pipe can be used in light hazard occupancies and residential buildings for wet systems only. The material also is rated for exposure in an air plenum.

BlazeMaster CPVC also can be used in antifreeze systems. However, the material is restricted to using glycerine antifreeze only. Glycol-type antifreezes cannot be used with BlazeMaster.

Because CPVC is a combustible material, it must be protected from the room or area being protected by the sprinkler system. The allowable protection barriers are 3/8-inch minimum thickness of gypsum wallboard and 1/2-inch minimum thickness plywood or lay-in ceiling tiles having a minimum weight of 0.35 pounds per square foot.

There are exceptions to the barrier protection for CPVC. When there is a smooth, flat ceiling, the CPVC can be attached directly to the ceiling without protection. The spacing between sprinklers is limited to 15 feet for this installation. There also are exceptions for exposing the CPVC in basements of residential sprinkler systems when the pipe is attached directly to a solid wood joist. These exceptions and the barrier protection requirements can be found in the third-party testing agency’s listing report and in the manufacturer’s installation instructions.

As part of the listing of CPVC, there are special hanger requirements. The hanger requirements identify the spacing between the hangers, as well as the support requirements for sprinkler drops.

A patented sprinkler fitting allows four connections to 1/2-inch PEX tubing


PEX Tubing

The latest material to be approved for sprinkler systems is PEX tubing. PEX is only approved for residential sprinkler systems that are designed and installed in accordance with NFPA 13D. Not all PEX tubing is approved for sprinkler installations. The PEX tubing must be specifically listed by a third-party testing agency as being acceptable for NFPA 13D sprinkler systems.

The joining of the PEX tubing also is a part of the third-party testing agency listing. All PEX joints are mechanical-type joints.

There are two types of sprinkler systems approved for PEX tubing. The first approval was of a manifold piping system. The manifold system used 1/2-inch PEX tubing. Special patented sprinklers allow the connection of three or four PEX tubes.

The manifold piping system can either be a stand-alone sprinkler system or a multipurpose piping system, which also serves plumbing fixtures.

The other PEX system is a standard piping system using 3/4-inch and 1-inch tubing. This system is piped like a typical sprinkler piping system.

Similar to CPVC, PEX tubing must be protected from the room or space being protected by the sprinkler system. The same barriers of 3/8-inch minimum thickness of gypsum wallboard and 1/2-inch minimum thickness plywood or lay–in ceiling tiles having a minimum weight of 0.35 pounds per square foot are required. Unlike CPVC, there are no exceptions to the barrier protection.

PEX tubing is required to be supported in accordance with the requirements of the plumbing code. This means that the horizontal spacing between hangers is 32 inches.

While there are only a few PEX manufacturers currently listed for sprinkler applications, it is anticipated that additional manufacturers will have their PEX listed in the near future.


Combined Piping

With limitations on CPVC, solder fittings and PEX tubing, engineers are designing more systems using multiple piping materials. It is not unusual to find a sprinkler system with steel pipe for the exposed piping and CPVC pipe for the piping behind the walls.

Sprinkler manufacturers, pipe manufacturers and fitting manufacturers are in the process of developing fittings and system components to make it easier to use multiple materials. For example, a copper press connection system with PEX tubing, or copper with CPVC. These new design features will present different options to the design professional when selecting a piping material for sprinkler systems.