Catwalk or Equipment Access? The ATG’s Function Test

A catwalk can look like a catwalk regardless of why it was built. For cost segregation, however, the 2025 IRS Cost Segregation Audit Technique Guide draws a meaningful distinction between a structure that serves the building and one designed only to access specific machinery or equipment. Building catwalks and mezzanines can be § 1250 property when they provide access between building levels, provide more than incidental working space, or are integrated into the building design. Equipment-access catwalks and mezzanines can be § 1245 property when they are designed and constructed only to inspect, repair, or operate specific machinery or equipment. For CostSegRx engineers, the key question is not what the structure looks like, but what function its design was intended to perform.

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Key Takeaways

• The ATG distinguishes building catwalks and mezzanines from structures designed only to access specific machinery or equipment.
• Building structures can remain § 1250 property when they provide building-level access, working space, or are integrated into the permanent building design.
• Equipment-access structures can qualify as § 1245 property when their only purpose is inspecting, repairing, or operating specific machinery or equipment.
• The same functional distinction applies to stairs and handrails that serve the building versus stairs and handrails designed only for specific equipment access.
• Engineers should examine the structure's intended function, relationship to the equipment, installation, permanence, and supporting construction documentation.
• Two similar-looking mezzanines can require different analysis when one provides general building access and the other exists solely to service specific equipment.
• The strongest classification follows the structure's actual purpose: what does it allow people to access, inspect, repair, or operate?

What Is the ATG's Catwalk and Mezzanine Distinction?

The ATG identifies two fundamentally different types of catwalks and mezzanines in its auto-manufacturing guidance.

The first is Catwalks and Mezzanines - Building.

This category includes decks and walks located in interstitial spaces between functional floors, as well as catwalks and mezzanines that provide access to different sections or levels of the building or provide more than incidental working space. These structures are generally designed to remain in place indefinitely, integrated into the building design, and require substantial time and effort to construct or remove.

The ATG classifies this type of structure as § 1250 property and 39-year nonresidential real property in the auto-manufacturing matrix.

The second is Catwalks and Mezzanines - Equipment Access.

These are structures designed and constructed only to provide access to inspect, repair, or operate specific items of process machinery or equipment. The ATG classifies these structures as § 1245 property under Asset Class 37.11, with 7-year property treatment in the auto-manufacturing matrix.

That single word, only, is important.

The equipment-access category is not simply a shorter-life classification for every platform near machinery.

The structure has to be designed and constructed only for access to specific machinery or equipment.

How Does the Function Test Work?

Start with the physical structure.

Then ask what it allows people to do.

A building catwalk may allow employees to move between different levels or sections of a facility.

A permanent mezzanine may provide storage, working space, maintenance access, or other usable building area.

Those functions connect the structure to the building.

The ATG specifically includes structures that provide more than incidental working space within the building category.

An equipment-access catwalk has a narrower purpose.

It may allow a technician to reach the upper portion of a machine.

It may provide access to inspect equipment.

It may allow workers to perform maintenance or repairs.

It may provide a safe operating position for a specific machine.

The important point is that the structure was designed and constructed specifically for those equipment-related functions.

This is consistent with the broader engineering principle that classification begins with function.

The question is not:

“Is this a metal platform?”

The question is:

“Why does this platform exist?”

Why Does the Distinction Matter?

Because a structure can look permanent and substantial without necessarily serving the building.

Conversely, a platform near equipment can look like machinery support while actually serving the building.

The ATG's building category focuses on integration with the building and the structure's broader access or working-space function.

The equipment-access category focuses on a structure designed and constructed only for access to specific machinery or equipment.

That means physical appearance is not enough.

A steel mezzanine with stairs, guardrails, and a substantial deck does not automatically become equipment-related property because a machine happens to sit below it.

Likewise, a narrow catwalk running beside a production line does not automatically become building property simply because it is permanently attached.

The engineering analysis has to establish what the structure was designed to accomplish.

This is one reason engineering asset classification is more useful than relying on construction labels alone.

The contractor may call something a mezzanine.

The engineer needs to determine what that mezzanine actually does.

Does the Same Test Apply to Stairs and Handrails?

Yes.

The ATG places building stairs and equipment-access stairs into parallel categories.

Stairs and Handrails - Building consist of flights of steps leading from one floor or level to another and related to the operation or maintenance of a building. The category includes railings and handrails and is § 1250 property.

Stairs and Handrails - Equipment Access are structures consisting of steps designed and constructed only to provide access to inspect, repair, or operate specific machinery or equipment. The category also includes railings and handrails and is § 1245 property in the auto-manufacturing matrix.

That parallel structure makes the ATG's logic especially clear.

The stair itself is not the decisive factor.

The function of the stair is.

A permanent stair connecting two building levels serves the building.

A stair constructed solely so a technician can reach a specific machine platform serves the equipment.

The handrail follows the same functional relationship.

This can matter in industrial facilities where equipment-access platforms, ladders, stairs, and catwalks are installed together.

Rather than treating the entire installation as one generic “steel structure” category, engineers can identify what each portion was designed to accomplish.

How Should Engineers Document Equipment Access?

The strongest analysis begins with the equipment.

What machinery does the catwalk or mezzanine serve?

Is there one specific machine?

Does it serve a defined group of interconnected equipment?

What maintenance or operating activity requires the access structure?

Was the structure included in the equipment manufacturer's installation requirements?

Was it designed as part of the original equipment installation?

Does it provide access to general building areas as well?

Then review the construction documentation.

Useful records can include architectural drawings, structural drawings, equipment layouts, manufacturer specifications, equipment installation requirements, maintenance access drawings, construction specifications, photographs, contractor records, and field observations.

The ATG's examination guidance emphasizes the importance of reviewing project records and actually inspecting challenged assets when necessary to understand their purpose, use, installation, and construction.

That is particularly useful for catwalks and mezzanines.

A drawing may identify a platform.

A site inspection can reveal why it exists.

For example, the field inspection may show that the platform has access doors or service points located directly above a specific machine.

Or it may reveal that the platform provides broad circulation between multiple building areas and contains substantial usable working space.

Those facts can materially change the engineering analysis.

The CostSegRx approach is straightforward:

Begin with engineering.

Identify what exists.

Determine why it exists.

Determine what it supports.

Then connect that conclusion to the applicable authority.

Can Two Similar Mezzanines Have Different Classifications?

Illustrative example only. Figures shown are estimated for demonstrative purposes only. Actual classifications, costs, asset classes, recovery periods, depreciation deductions, and tax results depend on the specific property, business activity, supporting documentation, engineering analysis, applicable authority, and taxpayer circumstances.

Assume a manufacturing facility contains two steel mezzanines.

Each costs $250,000.

They look almost identical.

Both have steel framing.

Both have stairs.

Both have guardrails.

Both are permanently installed.

But their functions are different.

Mezzanine A extends across a section of the facility and provides employee access between building areas. It also provides substantial working and storage space. The structural drawings show that it was incorporated into the building design.

Those facts are consistent with the ATG's Catwalks and Mezzanines - Building category.

Mezzanine B is a narrow platform constructed around one production machine. Its only purpose is to give technicians access to inspection points, controls, and maintenance locations on that machine.

Those facts are consistent with the ATG's Catwalks and Mezzanines - Equipment Access category.

The two structures cost the same.

They look similar.

They are installed in the same building.

But the engineering facts are different.

That is the point.

Cost segregation does not classify a structure because it has a particular appearance.

It classifies the property based on the relevant facts.

A study that simply labels both installations “mezzanines” may miss the functional distinction the ATG is designed to capture.

What Is the Most Important Catwalk and Mezzanine Question?

Do not start with:

“What is this structure made of?”

And do not stop with:

“Is it permanently attached?”

Instead ask:

What was this structure designed and constructed to let people access or do?

If it provides access between building levels, access to different building areas, or more than incidental working space, the ATG points toward the building category.

If it was designed and constructed only to provide access to inspect, repair, or operate specific machinery or equipment, the ATG provides a separate equipment-access category.

The same reasoning applies to stairs and handrails.

The classification follows the function.

For CostSegRx engineers, that means the investigation should connect the physical structure to the business activity it supports.

Review the drawings.

Inspect the installation.

Identify the equipment.

Understand the access requirement.

Document the purpose.

Then apply the appropriate property classification.

Classify the structure by what it was designed to let people do, not simply by what it looks like or where it is located.