IRS Cost Segregation Audit Technique Guide: What Owners Should Know

Commercial property owners researching cost segregation will eventually encounter the IRS Cost Segregation Audit Technique Guide, commonly called the Cost Segregation ATG. The guide is important because it explains how IRS examiners are instructed to understand, review, and examine cost segregation studies. It also provides extensive discussion of engineering methodologies, documentation, asset classification, depreciation, court cases, industry-specific assets, and examination procedures. But the ATG is often misunderstood as a set of automatic classification rules. Understanding what the ATG actually is, and what it is not, provides a better foundation for understanding cost segregation itself.

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

Key Takeaways

• What is the IRS Cost Segregation Audit Technique Guide?
• Is the Cost Segregation ATG official IRS authority?
• Why does the ATG say cost segregation studies are performed?
• Why is cost segregation an asset-level analysis?
• How does the ATG distinguish § 1245 and § 1250 property?
• What role does engineering play in a cost segregation study?
• Why does documentation matter?
• How does the IRS use the ATG when examining a study?
• What should commercial property owners learn from the ATG?
• How does the ATG relate to CostSegRx's engineering approach?
• What is the most important ATG principle to remember?

What Is the IRS Cost Segregation Audit Technique Guide?

The Cost Segregation Audit Technique Guide is an IRS publication designed primarily to help IRS examiners understand and evaluate cost segregation studies. The February 2025 publication states four primary goals: helping examiners understand why cost segregation studies are performed for federal income tax purposes, how the studies are prepared, what to look for during review and examination, and when identified issues may require further examination.

That purpose is important for property owners. The ATG is not simply a list of assets and depreciation periods. It provides a window into the questions an examiner may ask about how a study reached its conclusions.

The guide covers the legal framework behind cost segregation, common study approaches, characteristics of a quality study and report, examination procedures, depreciation, relevant court cases, construction processes, industry-specific guidance, and issue-specific subjects such as electrical distribution systems.

For an investor, that makes the ATG useful for understanding the depth of analysis that can exist behind a well-supported cost segregation study.

Is the Cost Segregation ATG Official IRS Authority?

No. This distinction should be clear whenever the ATG is discussed.

The 2025 guide expressly states that it is not an official pronouncement of law or the position of the IRS and cannot be used, cited, or relied upon as such. The introduction similarly explains that the ATG is not an official IRS pronouncement and may not be cited as authority.

That does not make the guide unimportant. It means it needs to be understood for what it is: an examination resource.

The ATG brings together legal history, court decisions, depreciation concepts, engineering approaches, examination procedures, and practical examples to help examiners analyze cost segregation issues. The underlying tax treatment still depends on applicable statutes, regulations, judicial decisions, administrative guidance, and the facts and circumstances of the property.

This distinction will matter throughout this CostSegRx ATG series. When we discuss an ATG position, we will identify it as ATG guidance rather than treating the guide itself as controlling legal authority.

Why Does the ATG Say Cost Segregation Studies Are Performed?

A commercial property is rarely one depreciable asset in an engineering sense. It may contain the building structure, site improvements, furniture, equipment, specialized electrical infrastructure, plumbing serving particular equipment, finishes, exterior improvements, and many other components.

The ATG explains that property often consists of numerous asset types with different recovery periods. To properly calculate depreciation, property is generally separated into individual items or groups having the same recovery periods and placed-in-service dates. When the actual cost of each item is known, that process can be relatively straightforward. When costs are available only in lump sums, estimating techniques may be necessary to segregate or allocate those costs among individual assets.

This is the fundamental purpose of a cost segregation analysis.

It is not simply an exercise in finding a percentage of a building that can be depreciated faster. The analysis involves identifying what property exists, determining the appropriate treatment of that property, and supporting the costs assigned to it.

That distinction is also why CostSegRx approaches cost segregation as an engineering inventory rather than a percentage exercise. Percentages are an outcome of the analysis. They are not the methodology used to reach the conclusion.

Why Is Cost Segregation an Asset-Level Analysis?

One of the most useful concepts for an investor to understand is that engineers classify assets, not buildings.

Consider a restaurant. Calling the property a restaurant does not tell an engineer how every component should be classified. The building contains components that support the building generally and other assets or infrastructure that may serve the restaurant's specific business operations.

The same principle applies to manufacturing facilities, medical offices, marinas, retail properties, self-storage facilities, and other commercial real estate.

The ATG itself illustrates this complexity. It explains that items such as carpeting, wall coverings, partitions, millwork, and lighting fixtures may or may not constitute § 1245 property depending on the particular facts and circumstances for which the project was designed.

That is why an asset's name alone is not enough.

A strong engineering analysis asks what the asset is, how it is installed, what it supports, how it relates to the building, and what documentation supports the conclusion. This functional approach is explored further in CostSegRx's article on what makes an asset § 1245 property.

How Does the ATG Distinguish § 1245 and § 1250 Property?

The distinction between § 1245 property and § 1250 property is central to cost segregation.

In its introductory discussion, the ATG describes a building as generally § 1250 property, with nonresidential real property generally using a 39-year recovery period and residential rental property generally using a 27.5-year recovery period. Equipment, furniture, and fixtures are described as tangible personal property generally treated as § 1245 property, which can have shorter recovery periods such as five or seven years.

For CostSegRx content, we describe applicable classes using precise depreciation terminology such as 5-year property, 15-year land improvements, QIP 15-year property, 27.5-year residential rental property, and 39-year nonresidential real property.

But identifying those classes is not simply a naming exercise. The ATG explains that complex and sometimes conflicting guidance, numerous court decisions, and the absence of bright-line tests can make distinguishing § 1245 from § 1250 property difficult.

That is one reason this ATG series will examine individual systems, classification principles, and court cases separately.

What Role Does Engineering Play in a Cost Segregation Study?

Engineering becomes important because a commercial building is a collection of physical assets and systems.

Someone must determine what actually exists. Someone must understand quantities, construction, installation, function, and relationships between systems. Costs then need to be identified or reasonably allocated to the property being classified.

The ATG recognizes multiple approaches to preparing cost segregation studies, ranging from detailed engineering approaches to less documented methods. Its discussion of quality studies also addresses preparer expertise, methodology, documentation, engineering takeoffs, unit costs, organization of assets, reconciliation, and treatment of indirect costs.

This is why CostSegRx describes its process as engineering-based cost segregation.

Our engineers begin with the physical property. What exists? Why does it exist? What does it support? How is it installed? What documentation is available? What costs can be supported?

Tax classification follows that investigation rather than driving it.

Why Does Documentation Matter in Cost Segregation?

A classification conclusion becomes much more useful when the engineering story behind it can be demonstrated.

Documentation may include architectural drawings, electrical drawings, mechanical and plumbing plans, site plans, equipment schedules, specifications, invoices, contractor records, photographs, owner interviews, cost records, and field observations.

The ATG's quality-study discussion specifically identifies the use of appropriate documentation as a principal element of a quality cost segregation study. It also discusses interviews, engineering takeoffs, cost reconciliation, indirect costs, schedules, engineering procedures, assumptions, and exhibits.

Documentation matters because two components that look similar can serve very different functions.

An electrical circuit serving general building lighting, for example, raises a different functional question from electrical infrastructure installed to serve specific qualifying equipment. The ATG devotes an entire issue-specific section to electrical distribution systems and functional allocation. CostSegRx discusses that issue in greater depth in Electrical Distribution Systems in Cost Segregation Studies.

The documents help engineers connect what they observe in the property to why the system exists and what it supports.

How Does the IRS Use the ATG When Examining a Cost Segregation Study?

The ATG gives examiners a structured framework for reviewing studies rather than assuming that every cost segregation report deserves the same depth of examination.

Chapter 5 addresses initial risk analysis, examination procedures, and other considerations. The guide explains that some studies may be evaluated without specialist assistance while other studies may require professionals with engineering, industry, or other specialized expertise. It encourages examiners to perform risk analysis early to determine the appropriate examination depth and whether additional assistance is necessary.

That reinforces an important ownership lesson: the final depreciation schedule is only one part of a cost segregation study.

How the classifications were developed matters. How costs were determined matters. The source documentation matters. The engineering reasoning matters.

Investors who want a deeper discussion of this subject can review cost segregation audit readiness and the role that study quality and documentation play in supporting classifications.

What Should Commercial Property Owners Learn From the ATG?

The biggest lesson is not that investors need to become IRS examiners.

They should understand that cost segregation is more sophisticated than assigning depreciation percentages to a property.

A commercial building contains assets serving different purposes. Those assets may have different construction characteristics, relationships to the building, functions, costs, and tax treatment. The job of a cost segregation study is to analyze those differences and support the resulting classifications.

This becomes especially important as a property evolves. Renovations, tenant improvements, equipment replacements, site work, electrical upgrades, and other capital projects become part of the property's engineering history.

Owners who preserve drawings, invoices, equipment schedules, photographs, and CapEx records give engineers more information to work with later. Cost segregation can therefore become part of a broader investment property management strategy, rather than an isolated tax exercise performed once after acquisition.

How Does the ATG Relate to CostSegRx's Engineering Approach?

The ATG and CostSegRx serve different purposes.

The IRS created the ATG to assist examiners in reviewing and examining cost segregation studies. CostSegRx prepares engineering-based cost segregation studies for property owners and their tax professionals. Nothing in the ATG represents an IRS endorsement of CostSegRx or any other study provider.

The connection is methodological.

Many subjects emphasized throughout the ATG are also central to how CostSegRx engineers think about a property: understanding the assets, evaluating function, reviewing documentation, determining costs, explaining classification reasoning, and reconciling the analysis to the property's basis and available cost information.

CostSegRx engineers do not begin with a desired percentage of 5-year property or 15-year land improvements. They begin with the property.

That is the principle behind engineering before tax. First understand the physical assets and their functions. Then determine the appropriate tax treatment supported by the facts, documentation, engineering analysis, and applicable tax framework.

What Is the Most Important ATG Principle to Remember?

If there is one idea to carry into the rest of this series, it is that cost segregation is an asset-level analysis.

The ATG demonstrates why. Commercial properties contain numerous assets, systems, and improvements. Classification can depend on facts and circumstances, and the guide acknowledges the complexity created by legal precedent and the absence of simple bright-line tests in important areas.

That is why good cost segregation begins with understanding the property rather than predicting a depreciation percentage.

Every building has an engineering story. The purpose of the analysis is to identify that story, document it, determine what the individual assets actually do, and support the classifications that follow.

That principle will serve as the foundation for the rest of the CostSegRx ATG Authority Series.