The International Association of Plumbing and Mechanical Officials (IAPMO) has published the 2021 editions of the Uniform Plumbing Code (UPC) and Uniform Mechanical Code (UMC) in both hard-copy and electronic versions, completing a three-year consensus development cycle accredited by the American National Standards Institute (ANSI).

Significant changes to the UPC include:

  • New Appendix N – Impact of Water Temperature on the Potential for Scalding and Legionella Growth;
  • New provisions for backflow prevention devices, assemblies and methods;
  • New provision for temperature limiting devices;
  • New guards and rails requirements for installation of equipment and appliances on roofs;
  • New requirements for the discharge of temperature and pressure relief valve piping;
  • New provision on leak detection devices;
  • New provisions for potable water pumps;
  • New standards for drain, waste and vent pipe and fittings;
  • New provisions for drain waste and vent cleanouts;
  • Circuit vent provisions have been updated and expanded;
  • Updated fuel gas provisions; and
  • Updated medical gas provisions, including reordering of categories for ease of use.

Significant changes to the UMC include:

  • New Appendix F – Geothermal Energy Systems;
  • New guards and rails requirements for installation of equipment and appliances on roofs;
  • New ventilation requirements for transient and nontransient occupancies;
  • New ventilation requirements for indoor air quality for residential occupancies;
  • Revisions to the requirements for air ducts, including factory-made air ducts and dampers;
  • New provisions for factory-built grease ducts;
  • New provisions for refrigeration systems, including pressure-limiting devices and hydrostatic expansion;
  • Revisions to the sizing requirements for natural gas and propane piping systems;
  • Modifications to the pressure rating requirements for hydronic piping applications;
  • New requirements for fuel gas piping appliance shutoff valves, test pressure and overpressure protection devices;
  • New tube fastener provisions for radiant heating and cooling;
  • New requirements for residential compressed natural gas (CNG) fueling systems; and
  • New fire-extinguishing equipment and carbon monoxide detection requirements for exhaust systems.

The 2021 Uniform Codes will once again be available electronically, meaning that if someone is working from home or in the field and left the code book at the office, it is accessible from a computer or mobile device.

The Uniform Codes are developed using IAPMO’s ANSI-accredited consensus development procedures. This process brings together volunteers representing a variety of viewpoints and interests to achieve consensus on plumbing and mechanical practices. The 2021 editions of the UPC and UMC mark the seventh time these codes have been developed in this manner. IAPMO urges its members and other interested parties to get involved in the process to ensure effectiveness in preserving the public’s health, safety and welfare through fair and balanced development of its codes and standards. Installers, plumbing and mechanical officials, the construction industry, engineers and manufacturers all benefit from a cooperative effort in developing codes.

Introduced in Los Angeles in 1928 and formally published as the Uniform Plumbing Code in 1945, the UPC is developed to govern the installation and inspection of plumbing systems as a means of promoting the public’s health, safety and welfare. Later published by IAPMO in 1967, the UMC provides the same governance for mechanical systems. Developed and subsequently republished at the conclusion of each three-year code cycle, the UPC and UMC are designed to provide consumers with plumbing, heating and mechanical systems that meet all applicable standards while, at the same time, allowing latitude for innovation and new technologies.

The public at large is encouraged and invited to participate in IAPMO’s open consensus code development process. A code development timeline and other relevant information are available at IAPMO’s website,

The 2021 UPC and 2021 UMC may be purchased through the IAPMO bookstore at:

Questions regarding the UPC can be directed to Enrique Gonzalez at (909) 230-5535 or For the UMC, contact Zalmie Hussein at (909) 218-8122 or email at