What the IRS Looks for in a Cost Segregation Study

One of the most common concerns property owners have about cost segregation is whether it will trigger an IRS audit. The short answer: a properly prepared cost segregation study does not increase your audit risk. In fact, the IRS has published detailed guidance — the Cost Segregation Audit Techniques Guide (ATG) — that outlines exactly what a quality study should contain. When your study meets these standards, it actually strengthens your tax position and provides documentation that would withstand an audit.

The IRS Audit Techniques Guide (ATG)

The IRS Cost Segregation ATG is a comprehensive document used by IRS examiners to evaluate cost segregation studies during audits. Published and periodically updated by the IRS, it establishes the standards that practitioners should follow. Rather than being something to fear, the ATG is actually a roadmap for creating a defensible study. If your study addresses all of the elements the ATG describes, you are well-protected.

The ATG identifies 13 principal elements that a quality cost segregation study should contain. These elements are what IRS agents look for when reviewing a study, and they form the gold standard for the industry.

The 13 Principal Elements of a Quality Study

1. Preparation by an individual with expertise and experience — The study should be conducted by someone with knowledge of engineering, construction, and tax law. This can include engineers, CPAs with cost segregation experience, or qualified professionals using validated methodologies.
2. Detailed description of the methodology — The study must clearly explain how costs were identified, classified, and allocated. The methodology should be consistent with IRS guidance and standard industry practice.
3. Use of appropriate documentation — Construction documents, blueprints, property inspection data, cost records, appraisals, and other supporting documents should be referenced and utilized.
4. Interviews with appropriate parties — The study should reflect knowledge gained from property owners, contractors, engineers, or other relevant parties who can provide insight into the construction and components.
5. Use of a common nomenclature — Asset descriptions should use consistent, industry-standard terminology that clearly identifies each component.
6. Explanation of the legal analysis — The study must include a legal analysis supporting the classification of each asset, referencing applicable tax code sections, regulations, revenue rulings, and case law.
7. Determination of unit costs — Costs should be allocated to individual components using recognized methods, not arbitrary percentages.
8. Identification of Section 1245 property — Personal property (5- and 7-year assets) must be specifically identified and distinguished from structural components.
9. Identification of Section 1250 property — Real property (27.5- or 39-year assets) remaining after reclassification must be clearly documented.
10. Identification of land improvements — 15-year property such as landscaping, paving, and site work must be separately identified.
11. Identification of indirect costs — Soft costs such as architect fees, engineering costs, and construction management should be properly allocated across asset categories.
12. Explanation of the treatment of special construction features — Items like clean rooms, specialized HVAC, or other unique building features require specific analysis.
13. Consistency with the taxpayer's financial records — The total costs in the study should reconcile with the taxpayer's cost basis and financial records.

Acceptable Methodologies: The IRS Ranking

The IRS ATG ranks cost segregation methodologies from most to least preferred. Understanding this hierarchy is important when evaluating the quality of a study:

1. Detailed Engineering Approach from Actual Cost Records — Uses actual construction costs, invoices, and contracts to allocate costs to individual components. Considered the gold standard.
2. Detailed Engineering Approach from Estimates — When actual cost records are not available, component costs are estimated using engineering techniques, cost manuals, and industry data.
3. Survey or Letter Approach — Uses contractor or vendor surveys to estimate component costs. Less detailed but still acceptable.
4. Residual Estimation Approach — Identifies and values certain components, then treats the remainder as structural. Less precise.
5. Sampling or Modeling Approach — Uses samples of properties to create models for similar buildings. Can be acceptable for large portfolios.
6. Rule of Thumb or Unsupported Approach — Uses arbitrary percentages without property-specific analysis. The IRS considers this unacceptable and will challenge studies using this method.

Safe Reclassification Ranges

While every property is different, the IRS and industry experience suggest that reclassifying 25% to 35% of a residential property's depreciable basis is within the normal and defensible range for most properties. Studies that claim significantly higher percentages may attract scrutiny unless they are supported by detailed documentation showing why the property has an unusually high proportion of personal property or land improvements.

For furnished short-term rentals, the upper end of this range (or slightly above) is common and defensible because STRs genuinely contain more 5-year personal property (furniture, appliances, electronics, linens) than unfurnished long-term rentals.

What Actually Triggers an Audit?

Cost segregation studies, when properly prepared, do not trigger audits. The IRS uses computer scoring (DIF scores) and other selection criteria to identify returns for examination. A large depreciation deduction will increase your return's score, but the deduction itself is legitimate and supported by your study documentation. What can cause problems:

• Unsupported reclassification percentages — Using "rule of thumb" percentages without property-specific analysis.
• Inconsistency with financial records — Study costs that don't match your property's actual basis.
• Missing documentation — Not retaining the study, supporting documents, or being unable to substantiate the classifications.
• Aggressive land value allocations — Understating land value to inflate the depreciable basis.
• Reclassifying structural components — Incorrectly classifying items that are inherently structural (load-bearing walls, roof structure, foundation) as personal property.

Documentation You Should Maintain

If your return is examined, you will need to produce your cost segregation study and supporting documentation. Keep the following on file:

• The complete cost segregation study report
• Property purchase documents (closing statement, purchase agreement)
• Construction documents and blueprints (if available)
• Photos of the property (interior and exterior, documenting personal property and land improvements)
• Records of any renovations or improvements
• Your tax preparer's workpapers showing how the study was applied to your return

For a comprehensive overview of what cost segregation is and how it works, start with our fundamentals guide. When you are ready to move forward, our step-by-step getting started guide walks you through the entire process.

Frequently Asked Questions