A client hands you a cost segregation report they hired someone else to produce, and the return is due in three weeks. You did not choose the provider, but the depreciation schedule going on the return is one you will be asked about if it is examined. The IRS publishes the document its own examiners use when reviewing these studies, which makes the review more structured than it first appears.
What the IRS Audit Techniques Guide Expects to See
The guide is the Cost Segregation Audit Technique Guide, Publication 5653, and Chapter 4 is the part that matters for a review. It sets out thirteen principal elements of a quality study. One caveat belongs at the front: it is examination guidance rather than legal authority, and states that it is not an official pronouncement of law and cannot be cited or relied upon as such. It is useful because it shows the framework examiners are instructed to apply. The IRS prescribes neither a format nor a methodology, so studies vary widely.
They fall into four practical groups:
| Group | Elements |
| Who did the work | Preparation by an individual with expertise and experience; interviews conducted with appropriate parties |
| How it was done | Detailed description of the methodology; determination of unit costs and engineering take-offs; use of appropriate documentation |
| How it is presented | Use of a common nomenclature; use of a standard numbering system; organization of assets into lists or groups |
| Whether it holds together | Explanation of the legal analysis; reconciliation of allocated costs to actual costs; treatment of indirect costs; identification of section 1245 property; related aspects including section 263A, accounting method changes and sampling |
The first element is the one the guide is most direct about. It states that a study prepared by a construction engineer is more reliable than one prepared by someone without an engineering or construction background. A report that does not identify its preparer or their qualifications is missing the element examiners look at first.
The fourth group is the most testable without engineering expertise. Reconciliation is an arithmetic check anyone can perform: allocated costs should tie to the settlement statement or construction cost, with no unexplained residual.
Methodology: Engineering Analysis Versus Estimates
Chapter 3 describes the range of approaches in use, from a detailed engineering analysis built on actual cost records at one end to a rule-of-thumb percentage at the other. The guide stops short of mandating one, but the distinction it draws is the single most useful thing a reviewer can test.
Ask what the allocation was built from. A study grounded in actual invoices, construction records and a physical inspection supports each classification with evidence. One that applies standard percentages by property type to a purchase price produces a number with no property-specific support behind it.
Look for the take-off. Documented unit costs and quantity take-offs are a named element. Estimates are not disqualifying, and the guide accepts that costs must be estimated where actual records are unavailable. What matters is whether the source of the estimates, the methodology and the reconciliation to total cost are all documented.
Check whether anyone visited the property. A site inspection is how a provider distinguishes decorative lighting from general lighting, or specialty electrical serving equipment from building electrical. Reports describing no inspection tend to classify by category rather than observation. Our comparison of engineering-based studies and DIY approaches covers this.
Reviewing the Asset Classifications and Support
With the methodology understood, the classifications can be reviewed on a sample basis.
Test the boundary items. High-judgment classifications worth sampling include land improvements against structural components, specialty electrical against building electrical, and decorative lighting against general lighting. Pull five or six of the largest items in the 5-year and 15-year classes and read the rationale for each.
Check the legal analysis is present. Classifications should be tied to authority, not asserted. A report that reclassifies items without citing the code sections, regulations, rulings or case law supporting the treatment leaves the reviewer to construct the defense later.
Watch for structural components in the short-life classes. Structural components placed in 15-year land improvement classes deserve specific review.
Confirm indirect costs are addressed. Capitalizable direct and indirect costs, such as architectural, engineering, permit and construction-related amounts, should be allocated to the property they relate to, with the treatment explained. Construction-period interest and other financing amounts are reviewed separately under their own capitalization rules. Silence on indirect costs is a gap rather than a simplification.
Checking the Form 3115 and Section 481(a) Adjustment
Where a look-back study changes an established depreciation method or recovery period treatment, implementation generally runs through a change in accounting method rather than amended returns. Not every prior-year correction is a method change; an isolated error does not become one merely because the property went into service earlier. Where a change is required, this is where a technically sound study can still produce a defective filing.
Confirm Form 3115 is included and determine whether the change qualifies for the automatic change procedures under current IRS guidance. If it does, verify the designated change number and the filing requirements. If it does not, confirm the applicable nonautomatic procedure. The report does not implement the change; the return has to carry the filing.
Recompute the section 481(a) adjustment at a high level. It should be the cumulative difference between depreciation claimed and depreciation allowable from the placed-in-service date to the beginning of the year of change.
Check the bonus depreciation rate used in the catch-up. Confirm the rate and eligibility under the law applying to the property’s acquisition date as well as its placed-in-service date, rather than the rate in force when the study was prepared. A property acquired and placed in service in 2024 carries 60% through the catch-up. Property acquired before January 20, 2025 but placed in service during 2025 can still fall under the phase-down rather than the restored 100% rate.
Confirm the year of change is the current year. Our Form 3115 instructions post covers the filing mechanics.
Questions to Raise With the Provider Before Filing
Most gaps are answerable, and it is better to ask before the return goes in than after an examination notice arrives.
- Who prepared the study, what are their engineering credentials, and did they visit the property?
- What cost records were used, and does the allocation reconcile to actual total cost?
- How were indirect costs treated, and what authority supports the 5-year and 15-year classifications?
- How were assets in the boundary categories distinguished?
- For a look-back, what bonus rate was applied and how was the section 481(a) adjustment computed?
A provider who answers these directly is generally one whose work will stand up. One who treats them as an obstacle has told you something useful.
If you want a second opinion on a study’s methodology, or would rather refer the work than review someone else’s, our resources for tax professionals cover how we work alongside CPA firms. You can also request a free analysis or read about our engineering-based cost segregation studies.
Frequently Asked Questions
What is the single most important thing to check in a study?
Whether the allocation is supported by property-specific evidence rather than standard percentages. The guide distinguishes engineering analysis from rule-of-thumb allocation, and reconciling allocated costs to actual total cost is the quickest way to test which one you have.
Does the IRS require a particular methodology?
No. The guide describes the range of approaches without mandating one and does not prescribe a report format. It is examination guidance rather than legal authority, but its thirteen principal elements show what examiners look for, and evidence-based approaches align with them far more closely.
What should I check on a look-back study?
Where a method change is required, that Form 3115 is included and the section 481(a) adjustment reflects the cumulative difference between depreciation claimed and depreciation allowable. Check the bonus rate against the law applying to the property’s acquisition and placed-in-service dates, not the rate in force when the study was prepared.
Which classifications draw the most scrutiny?
Items at the boundary between personal property and structural components. Land improvements, specialty electrical, and decorative versus general lighting all involve judgment, and structural components reclassified as 15-year land improvements warrant specific review.
What if the study is missing elements and the return is due?
Raise the gaps with the provider before filing, since most are answerable from working papers that exist but were not included in the report. Where a gap cannot be closed, that is a conversation with the client about filing position and about extending.
This article provides general information about federal tax rules and is not tax advice. Speak with your tax adviser about your specific circumstances.
