What the IRS Audit Techniques Guide Says About Cost Segregation

Why the guide exists

The IRS's Audit Techniques Guide for cost segregation, formally Pub 5653, exists because the agency's earlier position, that building components could not be depreciated separately from the structural shell, lost in Hospital Corporation of America v. Commissioner (109 T.C. 21, 1997). Once that argument failed, the IRS shifted its focus from whether cost segregation is valid to how well a given study is executed. The ATG is the result: a manual for its own examiners on what a properly done study contains and how to evaluate one.

That framing matters for owners evaluating a provider. The guide is not a set of hoops designed to make the deduction hard to claim. It is closer to a quality rubric, and a study built to satisfy it is, by definition, built to hold up under the exact review process the guide describes.

The methodology hierarchy the guide describes

The ATG ranks cost segregation methods by reliability. At the top sits detailed engineering from actual cost records, reviewing a building's real construction costs and drawings component by component. Just below that sits detailed engineering from a cost estimate, the same component-level review applied when original cost records are incomplete, common on older or acquired properties. Lower on the list sit survey or letter approaches and, at the bottom, cost-estimating or default-percentage approaches that apply a lookup-table figure by property type without reviewing the specific building.

This hierarchy is the reason engineered studies cost more than software-based ones: the guide itself treats them as different tiers of reliability, and an examiner is trained to weigh a study accordingly. A report near the top of that hierarchy is not just more expensive, it is the version the IRS's own document says to trust more.

The quality elements an examiner actually checks

Beyond the methodology tier, the guide describes specific quality elements an examiner looks for in a study under review.

• Component-level detail. Each reclassified item, carpet, cabinetry, decorative lighting, site paving, identified individually rather than bundled into a vague category.
• A documented cost allocation method. How the cost of each component was derived from the building's total basis, not an assumed percentage.
• Consistency with the building's actual construction. The study's conclusions should match what the building actually is: a restaurant's kitchen equipment allocation should look like a restaurant's kitchen, not a generic template.
• Correct class lives. Items placed in the 5-year, 7-year, or 15-year land improvement bucket according to the property's actual function, with structural items, including the roof and central HVAC, correctly left on the 39-year (commercial) or 27.5-year (residential) schedule rather than misclassified as short-life property.
• Qualified preparer involvement. The guide favors studies where someone with construction, engineering, or cost estimating expertise did the actual classification work.

How an engineered report maps to each element

A study built to the ATG standard answers each of these elements directly rather than leaving them for an examiner to ask about later. Component-level detail comes from an engineer or trained reviewer classifying the building's actual carpet, fixtures, electrical runs serving specific equipment, and site improvements, not applying a database percentage. Cost allocation is documented per component. Construction consistency is built in because the classification starts from the specific building's plans, photos, or site review, whether that is a commercial site visit or, for a short-term rental, the listing photos from Airbnb or VRBO that feed the classification without requiring the owner to do anything.

Those ratios come from real quoted engineered studies: a Medical Clinic study on a $1,404,500 building basis produced $241,839 in first-year deductions for a $10,000 fee, and a Mid-Rise Office study on $2,971,345 in basis produced $479,220 for a $12,000 fee. Neither number is the point of the ATG itself, but both studies were built the way the guide describes, which is exactly why the numbers have documentation behind them.

Why the guide rewards documentation, not aggressiveness

A common misreading of the ATG treats it as a target to hit: move as much basis as possible into 5-year property, since faster depreciation is the goal. That misreads what the guide actually values. The quality elements it describes reward accurate, documented classification, not maximum reclassification. A study typically shifts about 15 to 35% of building basis into faster schedules, and a study landing above that range needs a specific, documented reason tied to that building's actual construction, not simply an assumption that more is better. A study that quietly claims 45% across every property type is not more thorough by the ATG's standard, it is less credible, because the documentation would need to explain construction differences that a uniform percentage cannot.

What the guide does not do

The ATG does not create new law, set a maximum reclassification percentage, or guarantee that a study built to its standard will never be questioned. It is a reference document for examiners, and an examiner can still ask questions about any study, well-documented or not. What a properly built study changes is how quickly and how completely those questions get answered. See what actually happens if a study gets questioned during exam for that process, and what audit defense of a report means for the precise scope of who answers those questions and who does not.

Getting a study built to the guide's own standard

A free Preliminary Benefit Estimate at /qualify starts from an engineering-based approach, the tier the ATG itself ranks highest, and models a property's likely first-year number before any commitment.

Whether a specific study's documentation would satisfy an examiner in a given case is ultimately a matter your CPA weighs alongside the study itself. What the ATG describes, and what an engineered study delivers, is the documentation standard the IRS's own examiners are trained to look for.

Frequently asked questions

What is IRS Publication 5653?

Publication 5653 is the IRS's Audit Techniques Guide for cost segregation, a document written for its own examiners describing the methodology hierarchy and quality elements of a properly done study. It is a reference guide, not a taxpayer form or a set of regulations.

Does the IRS require a specific cost segregation method?

No. There is no legal requirement to use any particular method. The ATG describes a hierarchy of reliability, from detailed engineering at the top to rough percentage estimates at the bottom, and notes that examiners should weigh a study's methodology accordingly.

Is a cost segregation study that follows the ATG audit-proof?

No study is audit-proof in the sense of guaranteeing no questions will ever be asked. A study built to the ATG's quality elements is positioned to answer an examiner's questions quickly and completely, because the documentation the guide describes is already built in.

Does the ATG apply to residential rental studies too?

The ATG's quality principles, component-level detail, documented cost allocation, and construction consistency, apply regardless of property type. For short-term rentals, that classification work is done from listing photos rather than a site visit, but the same documentation standard governs the result.