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IAPMO and ASPE Co-publish Capacities of Stacks and Horizontal Drains in Storm Drainage Systems White Paper

Ontario, Calif. — The International Association of Plumbing and Mechanical Officials (IAPMO®) and the American Society of Plumbing Engineers (ASPE) have co-published White Paper 2-2024: Capacities of Stacks and Horizontal Drains in Storm Drainage Systems.

The sizing for storm drainage systems is dependent upon flow capacity equations used to calculate velocities and flow rates in pipe conduits. One of the variables in the equations is the coefficient of roughness. This white paper explores how the roughness of different types of material will change the computational results that are dependent upon the roughness coefficient of the pipe.

“Storm drainage systems play a vital role in building resiliency as they convey water off the roof, said IAPMO Vice President of Technical Services and Research Christoph Lohr, PE. “Studying storm piping systems is important to make sure these systems are not undersized, as the weight of water on a roof could exceed design parameters and fail, which could be catastrophic. With changing weather patterns, particularly rainfall rates increasing in many locations, revisiting assumptions and validating the equations of how storm piping systems are sized is vital. We are thankful to our partners at ASPE for collaborating with us on this white paper, which shows the depth of plumbing expertise exhibited by both organizations and their dedication to public safety.”

The IAPMO/ASPE white paper is available for free download HERE

Founded in 1926, the International Association of Plumbing and Mechanical Officials is a global leader in providing uniform codes for the plumbing and mechanical industry. IAPMO protects health and safety, supports sustainability and emerging technology, and delivers code education.

The American Society of Plumbing Engineers (ASPE) is the international organization for professionals skilled in the design, specification and inspection of plumbing systems. ASPE is dedicated to the advancement of the science of plumbing engineering, to the professional growth and advancement of its members and the health, welfare and safety of the public.

For questions, please contact Christoph Lohr at (909) 731-0219 or christoph.lohr@iapmo.org; or Hugo Aguilar at (909) 472-4111 or hugo.aguilar@iapmo.org.


IAPMO develops and publishes the Uniform Plumbing Code®,the most widely recognized code of practice used by the plumbing industry worldwide; Uniform Mechanical Code®; Uniform Swimming Pool, Spa and Hot Tub Code®; and Uniform Solar Energy, Hydronics and Geothermal Code — the only plumbing, mechanical, solar energy and swimming pool codes designated by ANSI as American National Standards — and the Water Efficiency Standard (WE-Stand)™. IAPMO works with government, contractors, labor force, and manufacturers to produce product standards, technical manuals, personnel certification/educational programs and additional resources in order to meet the ever-evolving demands of the industry in protecting public health and safety.

Last modified: May 29, 2024