Building Plumbing vs. Process Plumbing: Where the ATG Draws the Line

When does plumbing stop being part of the building and become property serving a specific process? The 2025 IRS Cost Segregation Audit Technique Guide distinguishes general building plumbing from separate plumbing systems necessary to and used directly with specific machinery, equipment, or processes. That distinction can apply to piping, pumps, tanks, filters, valves, drains, specialty-water systems, natural gas lines, and related components. But the presence of specialized-looking pipe does not automatically establish § 1245 property. For CostSegRx engineers, the classification begins by tracing the system, identifying exactly what it serves, and determining whether it provides a general building function or a separate process function.

Wondering how much tax you could save with cost segregation? Let’s find out. Schedule a Cost Segregation Strategy Call today.

Key Takeaways

• Building plumbing generally provides water, waste removal, gas distribution, and other services associated with operation or maintenance of the building.
• Process plumbing consists of separate systems necessary to and used directly with specific machinery, equipment, or a process.
• A pipe, valve, drain, or gas line cannot be classified from its component name alone because the system it serves matters.
• Engineers can trace piping, pumps, tanks, filters, drains, valves, specialty-water systems, and equipment connections to establish actual function.
• General building applicability and accessibility can distinguish building plumbing from a dedicated process system.
• Two physically similar piping systems can require different treatment when one serves the building generally and the other directly serves qualifying process equipment.
• Plumbing classification begins with the function and boundaries of the installed system, not simply the fact that the property is piping.

What Does the ATG Treat as Building Plumbing?

Building plumbing supports the operation and maintenance of the building itself.

The ATG's industry guidance includes systems that supply water and remove liquid and water-borne waste.

It can also include natural gas distribution associated with building equipment.

Typical building-plumbing components can include plumbing fixtures, water heaters, drains, roof drains, piping, fittings, valves, traps, supports, and insulation.

These components may look very similar to property used in a specialized process.

The distinction is what the system is doing.

A domestic water line supplying sinks, restrooms, janitorial fixtures, and other general building uses is performing a building function.

A sanitary waste system collecting waste from general plumbing fixtures is performing a building function.

A roof-drain system removing rainwater from the building is performing a building function.

Natural gas piping supplying general building equipment can also be part of the building system.

In the ATG's auto-manufacturing guidance, building plumbing is treated as § 1250 property and recovered as 39-year nonresidential real property.

The important lesson is that plumbing does not become specialized property simply because it contains substantial piping, valves, drains, or other components.

The engineer has to understand the system's function.

What Does the ATG Mean by Process Plumbing?

Process plumbing serves a different purpose.

The ATG describes process plumbing as separate plumbing systems necessary to and used directly with specific machinery, equipment, or a process.

That definition contains two important ideas.

First, the system is separate from general building plumbing.

Second, it has a direct relationship to the machinery, equipment, or process it serves.

Depending on the facility, process plumbing can include specialized piping, pumps, tanks, filters, valves, drains, supports, insulation, and related components.

The ATG also identifies dedicated specialty-water systems, including deionized water systems, as examples within process plumbing.

Dedicated natural gas piping serving process machinery can also fall within this analysis.

The physical property may still look like plumbing.

There may be pipes.

There may be valves.

There may be pumps.

There may be drains.

What changes is the system's function and relationship to the taxpayer's process equipment.

That is why “process plumbing” is an engineering description of a system relationship, not simply a different name for a pipe.

Why Can't You Classify a Pipe by Its Name?

A pipe does not reveal its tax classification by appearance alone.

Consider two steel natural gas lines installed in the same manufacturing facility.

One supplies building heating equipment.

The other supplies a specialized production machine that requires natural gas as part of the manufacturing process.

The material may be similar.

The installation method may be similar.

The fittings may be similar.

The visual appearance may be nearly identical.

But the systems do not necessarily perform the same function.

The same issue can arise with water.

One line may supply ordinary restroom fixtures.

Another may be part of a dedicated specialty-water system required by production equipment.

Likewise, one drain may belong to the building's sanitary system while another may be part of a separate process system associated directly with production machinery.

The engineer therefore needs more than a photograph of the component.

The engineer needs context.

Where does the line originate?

Where does it terminate?

What equipment does it serve?

Does it serve multiple general building uses?

Is it part of a separate process network?

Would the system exist in substantially the same form without the process equipment?

Those questions help establish what the installed property actually does.

How Do CostSegRx Engineers Trace Process Plumbing?

A plumbing classification can be approached as a system-tracing exercise.

CostSegRx engineers may begin with plumbing plans, process-flow diagrams, equipment schedules, mechanical drawings, utility plans, specifications, and construction documents.

Those records can identify system types and intended destinations.

Field investigation can then test the drawings against actual conditions.

An engineer may trace piping from its source through pumps, tanks, filters, valves, branches, and other components.

The engineer can identify the equipment connected at the end of the system.

Pipe labels can help establish the material being transported.

Equipment nameplates and process documentation can help establish why the utility is required.

The engineer can also examine whether the system is isolated from general building plumbing or interconnected with a broader building network.

For specialty-water systems, that might mean tracing the system from treatment equipment through storage and distribution to the specific production equipment using the water.

For natural gas, it might mean determining whether a branch serves ordinary building heating or is dedicated to manufacturing machinery.

For drainage, it can mean identifying whether the drain is part of the general sanitary system or is directly associated with a specific process.

The ATG recognizes the importance of this engineering work.

It notes that studies allocating estimated costs between § 1245 property and § 1250 property, particularly electrical or plumbing component systems, typically require an engineer experienced in construction and construction estimating.

What Does General Building Applicability Tell You?

The ATG places an important limit around process plumbing.

Process plumbing does not simply mean any plumbing that happens to reach business equipment.

The guidance excludes plumbing hook-ups, natural gas distribution systems, and sewer systems that are of general building applicability and accessibility from the process-plumbing category.

That language helps define the boundary.

A broadly distributed utility network may serve the building in a general way even when individual pieces of equipment connect to it.

The existence of an equipment connection therefore does not automatically transform the upstream building network into process plumbing.

The engineer should determine where the general system ends and where a separate process-specific system begins.

This resembles the boundary problem encountered in electrical analysis.

As explained in Branch Circuits vs. Building EDS, an engineer should not automatically treat one continuous utility path as a single classification unit.

Instead, the system can be traced in layers.

For plumbing, the questions include whether the piping is broadly available for building use, whether it is dedicated to a process, and whether it is necessary to and used directly with specific machinery or equipment.

The classification follows the supported system boundary.

Can Similar Pipes Have Different Recovery Periods?

Illustrative example only. Actual classifications, system boundaries, costs, recovery periods, depreciation deductions, and tax results depend on the specific property, engineering analysis, documentation, applicable authority, and taxpayer circumstances.

Assume a manufacturing facility contains two natural gas piping systems.

System A distributes natural gas to rooftop heating equipment and other equipment used to condition the building.

System B is a separate gas line installed specifically to supply qualifying production machinery.

Assume each system has a supported installed cost of $150,000.

The two systems may use similar pipe.

They may use similar fittings.

They may even run through portions of the same facility.

But their functions differ.

System A supports operation of the building.

For a commercial manufacturing facility, supported building plumbing can be part of 39-year nonresidential real property.

System B directly serves the production process.

If the facts and applicable authority support treatment as process plumbing associated with qualifying machinery, it can be § 1245 property and may follow the appropriate recovery period associated with the property it serves.

The point is not that natural gas piping is automatically short-life property when connected to equipment.

The point is that the function and system boundary must be established.

Now assume someone classified both systems solely from the construction estimate under a single line item labeled “natural gas piping.”

That cost record would identify what was purchased.

It would not necessarily identify what each portion of the system serves.

Engineering analysis supplies the missing relationship between the cost and the function.

What Is the Most Important Process-Plumbing Question?

The most useful question is not:

Is this plumbing?

The better question is:

What does this plumbing system serve?

From there, the engineer can determine whether the system provides water, waste removal, gas, drainage, or another utility for general building operation.

Or the engineer may find a separate system necessary to and used directly with specific machinery, equipment, or a process.

That distinction can require tracing the system from its source to its end use.

It can require reviewing plans.

It can require identifying pumps, tanks, filters, valves, drains, and connections.

It can require determining whether the utility is generally accessible throughout the building or dedicated to a particular process.

And it can require separating general building infrastructure from downstream process-specific property.

For CostSegRx engineers, that physical and functional evidence comes before the classification conclusion.

A pipe is not classified by being called plumbing. Engineers trace what the system serves, determine whether it provides general building service or a separate process function, and classify the supported system from those facts.