How to Comply With the 2018 International Plumbing Code


The International Plumbing Code establishes minimum regulations for plumbing facilities while still accepting innovative products, materials, and systems as necessary. It serves as the foundation of many state codes.

It was created through an effort led by a committee of plumbers and code officials using the ANSI consensus development process, bringing together multiple interests such as consumers, enforcement authorities, installers/maintainers, insurance providers, manufacturers, and research/standards/testing labs.

Water Piping Sizing

Pipe sizing refers to the practice of determining how many water supply fixture units (WSFUs) a pipe can serve so as to meet demand without overflow or other complications. Calculations usually involve factors such as fluid velocity, water demand, static pressure loss, friction loss, and roughness – among many others. For accurate sizing results, the best approach is using custom quick-sizing tables tailored specifically for pipe material sub-type tank valve and C factor requirements.

Ductile iron pipe is used in plumbing systems to transport water, sanitary sewer waste, and storm drain water, as well as particular waste such as grease. Additionally, this material is commonly employed for medical gas distribution, such as oxygen, nitrogen, and nitrous oxide, as well as compressed air for medical uses – this calculator is based on AWWA C901 and ASTM D 2239 standards.

Plastic piping is often found in domestic water systems. Rated similarly to metal pipes, however, plastic is more durable and does not expand/contract as rapidly when temperature fluctuations occur, with a lower pressure rating at higher temperatures. Our calculator utilizes AWWA standards for plastic pipe types DR11, DR13.5, and SIDR11.5 (UPVC/PP), though it only includes smaller pipe sizes as these tend to be used more commonly for domestic systems.

Pressure Requirements

Designing plumbing piping in nonresidential buildings involves many variables that determine how much water each fixture requires, including occupancy type, pressure availability from its source, special equipment requirements, and building layout. It is essential to understand how sizing methods employed by Uniform Plumbing Code (UPC) and International Plumbing Code (IPC) codes affect this decision.

Water supply lines must also be appropriately sized to ensure user safety, with investigations showing that many cases of waterborne disease emanating from improperly chlorinated or disinfected water supplies. To protect users against this happening, certain pressure must remain throughout the system to maintain this safety precaution.

For optimal results, the ideal method is to install either a pressure-reducing valve or backflow preventer into your system to reduce total system pressure and protect trap seal fittings on fixtures. In addition, the ICC recommends adding another pressure-reducing valve downstream of any backflow preventers in order to decrease overall system pressure further.

Pressure-reducing valves can also help building owners reduce utility bills. According to an ICC study, such devices can lower system pressure by as much as 30%, resulting in reduced utility bills.

An energy-saving reducing valve is a brilliant addition to any plumbing system, whether residential or commercial. It can improve energy efficiency while protecting the environment through reduced carbon emissions and cost reductions.

Water Hammer Arrestor Placement

Banging noises when switching off a fixture or appliance are most commonly caused by sudden changes in water pressure. Sudden fluctuations cause shock waves throughout the pipes that can damage fixtures. Install a water hammer arrester that will absorb shock waves and stop banging altogether. These devices are inexpensive and easy to set up; all it requires to work correctly is turning off your main valve. Before any plumbing work commences, an arrester should be located as close as possible to where the water hammer occurs – for example, upstream of isolation valves or in series elbows prior to tall risers.

Water hammer arresters should be installed in most residential piping systems to provide added protection for fixtures, equipment, or apparatus that might experience severe shocks. They are available at most hardware and home centers for around $10 each and installed by cutting into the pipe, adding an adaptor fitting, threading on an arrester, and tightening with a small wrench – though be careful not to over-tighten and risk leaks!

Water hammer arresters should be installed at every 20-foot section that contains multiple fixtures served from one branch line in commercial installations, particularly restrooms and public buildings where multiple fixtures share one branch line. It should be easy to determine this placement using the guidelines outlined in PDI-WH201 for fixture units as a guideline for placement and sizing.

Minimum Pipe Sizes

Minimum pipe sizes required for a plumbing system depend on several factors, including fixture count and length of pipe run. Furthermore, building type (residential, commercial, or mixed-use) also influences these calculations.

Residential and commercial water systems should aim for maximum fluid velocities of 4-8 feet per second (fps), while less-than-ideal speeds, between 2 and 6 fps, may lead to erosion over time and noise during operation.

Pipes can be sized based on pressure drop, velocity, or both criteria; our calculator allows you to select your preferences.

When selecting the pipe material and type, make sure that a standard size exists within that material type – for instance, the copper pipe has an outside diameter of 0.625 inches and an interior diameter of 0.545 inches.

The 2018 International Plumbing Code, developed by the International Code Council and adopted at state or local levels across the US, Guam, and Puerto Rico by their jurisdictions, sets minimum regulations to protect building occupants’ health, safety, and welfare through plumbing systems and components. As part of ICC’s family of codes, it works seamlessly together; to learn more, visit