Plumbing Design Of Residential Sprinklers
There was a lot of excitement last September when the ICC membership voted to mandate residential sprinkler systems for all one- and two-family dwellings and townhouses. All sorts of proclamations were made regarding how much money everyone would make in this industry.
Before you get too excited, stop and understand what this first step really means. Residential sprinklers were merely added to the 2009 International Residential Code (IRC). The mandate for one- and two-family dwellings becomes effective Jan. 1, 2011, if a jurisdiction adopts that part of the code. Townhouses become mandated immediately; again, if the jurisdiction adopts that part of the code.
The important step that must now be taken is to have states, and local jurisdictions, adopt the 2009 IRC. Don’t think the homebuilders will let that happen without a fight. They will be testifying before the various governmental agencies that the sprinkler requirement must be removed because of affordable housing. In other words, 3,000+ fire deaths a year is an acceptable number if it lowers the cost of housing.
Another important part of the 2009 IRC is what has been dubbed “Section P2904”. This is the new section that adds the sprinkler requirements to the plumbing section of the IRC. Hence, you can follow this section rather than NFPA 13D. Although NFPA 13D is referenced in the section as an option, the result is that the system must either comply with P2904 or NFPA 13D.
This new section includes requirements for both multipurpose residential sprinkler systems and stand-alone systems. A multipurpose piping system is a sprinkler system that is combined with the cold water distribution system.
There has been speculation that the most common system will be a multipurpose piping system. Quite frankly, both systems can be installed inexpensively. It really depends on the house. For example, in homes on a well or a limited-pressure public main, a stand-alone system may be less expensive to install.
The concept of P2904 is to allow either the plumbing contractor or sprinkler contractor to design and install the residential sprinkler system without the need for an engineer. All of the information regarding design parameters can be found in the new section. That includes hydraulic calculations.
Proper Design And InstallationThe most important part of any sprinkler system is the proper placement of the sprinklers. The sprinklers must provide complete coverage of the living spaces. Consideration must be given for obstructions that may block the flow of water from the sprinkler. All of this is addressed in Section P2904.
Once you properly position the sprinklers, the rest is easy. You simply connect pipe to the sprinklers and size the pipe accordingly. Of course, every plumbing contractor can run piping from the main to the sprinklers. You also know how to protect the piping from freezing.
When presenting the hydraulic calculation part of P2904, it was noted that plumbing contractors already know how to size the plumbing water piping systems in one- and two-family dwellings. The sprinkler hydraulics are actually easier than the water pipe sizing calculations. There are no fixture unit values. The sprinkler has a published flow rate based on the area of coverage. That is the value you use to size the pipe. The piping system must be sized for the discharge of either one or two sprinklers - that’s it.
The current residential sprinklers on the market have a flow rate that ranges from a low of 8 gpm for an area of coverage of 12 feet by 12 feet, to 20 gpm for an area of coverage of 20 feet by 20 feet.
The most common flow rate that I use is 13 gpm. This is the flow rate for a very popular sprinkler. The flow rate applies for an area of coverage ranging from 12 feet by 12 feet to 16 feet by 16 feet. When using this particular sprinkler, the flow rates for the piping design would be 13 gpm and 26 gpm.
I should mention that the pressure requirement for this sprinkler is 7 psi, well below the pressure requirements for plumbing fixtures.
The next question always asked is, “How much flow do you add for the plumbing system?”
The answer: basically, none! The only flow that would impact the sprinkler system is automatic systems such as a lawn sprinkler system or the backwash of a water softener.
However, smart contractors will install bypass valves that will not allow these systems to operate in the event of a fire. Then you are back to not worrying about a plumbing flow. Thus, you design a multipurpose piping system for two values - one size for the sprinkler system, the other for the plumbing. Whichever size is larger would be the size of the piping system.
Simplifying CalculationsP2904 provides a number of tables for calculating the pipe size. The tables simplify the pressure loss calculations for the given flow rate of the sprinkler. The number at the end of the calculation is a distance. That distance determines the maximum length of pipe that can be installed from the entrance of the water supply into the home to the furthest sprinkler. That is how simple the sizing is using this new section in the IRC.
For most homes, the sprinkler sizing will be 3/4 inch for one sprinkler and 1 inch for two sprinklers. However, it is possible to design the entire system (for two sprinklers) using a 3/4-inch pipe. It depends on which sprinkler and area of coverage is selected.
It is possible that the standard water service will become 1 inch rather than 3/4 inch. However, many homes already have a 1-inch water service. Again, based on the sprinkler, a 3/4-inch service can work just fine.
It will become important for plumbing contractors that want to enter the residential sprinkler market to become educated on the sprinkler requirements. It is anticipated that state licensing boards will mandate continuing education if a plumbing contractor wants to also install residential sprinklers. There may also be a requirement to take a certification test.