A popular statement made about the plumbing code is it is a book for the plumbing contractor. Of course, that statement isn’t true.

The plumbing code is adopted by a jurisdiction as the legal requirements for regulating plumbing systems. As such, the plumbing code is used by many more individuals than plumbers. This group includes the jurisdiction, plumbing inspector, developer, architect, plumbing engineer, plumbing contractor, the public, the owner and finally the attorneys. Do not discount the last one. If it’s a legal document, it is used in a court of law.

At a recent model code meeting, I had a long discussion regarding the engineering requirements in the plumbing code. For ease of review, let me first address the engineering requirements in the ICC International Plumbing Code. I will cover the IAPMO Uniform Plumbing Code in a future column.

Chapter 1 of the IPC has requirements for the submission of construction documents. Section 106.3.1 reads, in part: “Construction documents, engineering calculations, diagrams and other such data shall be submitted in two or more sets with each application for a permit.” It further states construction documents shall “be prepared and designed by a registered design professional where required by state law.”

What this says is the construction documents are the responsibility of the plumbing engineer or design professional. Every state requires engineering plans to be prepared by a licensed professional engineer. However, when it comes to plumbing plans, many states have exceptions allowing licensed plumbers to design small systems or licensed plumbing designers to design any plumbing system. Again, this is a state provision which the code acknowledges.

The exceptions

What is a mandatory code section without a good exception? The exception to this section is the allowance by the code official to waive the submittal of construction documents when they are unnecessary to determine conformance with the code. The purpose of this section is to allow the inspector to waive the submittal of plans for small projects such as when a water heater is being installed, a new sink is being added or similar types of installations. Unfortunately, I’ve seen this section used to waive the requirements for plumbing plans for a single-family dwelling. The comment statement is, “We’ll catch it in the field.” However, realize that is not the purpose of the exception!

You may be asking why use the term “construction documents?” What happened to “plans and specifications?” I could say blame it on the architects, but the codes switched to the term “construction documents” to use the more updated indicator of all the documents required to construct a building.

Chapter 2 has a definition of construction documents that reads: “All of the written, graphic and pictorial documents prepared or assembled for describing the design, location and physical characteristics of the elements of the project necessary for obtaining a building permit. The construction drawings shall be drawn to an appropriate scale.”

This definition also acknowledges most of our plans are electronically prepared. We’ve done away with drawing boards in engineering offices. Additionally, plans often are submitted to the building department electronically.

Mixed messaging

After Chapter 1, it appears engineering design is ignored with the code only identifying requirements. However, there are many other sections that address engineering design. The first appears in Chapter 6, regarding the design of the water-distribution system. Section 604.1 states: “The design of the water distribution system shall conform to accepted engineering practice. Methods utilized to determine pipe sizes shall be approved.”

The section almost appears as double speak. OK engineer, design the water-distribution system so it works correctly, and by the way, the inspector will determine if the method you use for sizing is acceptable. Ultimately, the engineer is responsible for the design. Notice, the code never tells you how to control the water, how to size pumps, what pressure control valves are required, etc. That is all under the purview of the engineer.

For the design of the DWV system, there are three sections that talk about engineering: 714.1, 919.1, and 920.1. Both 714.1 and 920.1 allow the system to be designed by computer design methods, but the computer design methods must be approved by the inspector. It is interesting that you can engineer with the computer but not a calculator or slide rule. At least there is a requirement that allows the engineering of the DWV system.

Section 919.1 allows engineering the vent sizing in accordance with the reduced-size venting method developed at NIST. That is the other engineering design that can be used.

Under storm drainage, there are no requirements specifically referencing engineering design. However, the new sizing method requires engineering to properly size the system. You have to calculate the amount of water that needs to come off the roof and size the piping accordingly. Hence, the engineer has to analyze the roof design and determine how much water is getting to that drain.

The one remaining section I skipped over is the most powerful section in the code regarding engineering design. Section 316 is entitled “Alternative Engineered Design.” The main requirement for this section reads: “An alternative engineered design shall conform to the intent of the provisions of this code and shall provide an equivalent level of quality, strength, effectiveness, fire resistance, durability and safety. Material, equipment or components shall be designed and installed in accordance with the manufacturer’s instructions.”

Basically, you can design any plumbing system you want provided it works. This allows you to be an engineer and ignore what you may consider silly or petty requirements in the code. However, whenever you use the alternative engineered design, you must justify every aspect of that design. That shouldn’t be a problem for a competent engineer. The bottom line in any engineered design is protection of public health, safety, and welfare.

Take advantage of the opportunities the code provides to the engineer. The IPC recognizes the ability of the plumbing engineer to properly design plumbing systems. Be sure to prove the code right. Design a plumbing system that performs correctly for the life of the building.