DIY Cost Segregation vs. Engineering-Based Studies: What the IRS Actually Requires

The cost segregation industry has traditionally been the domain of engineering firms charging $5,000–$15,000 per study. In the last several years, DIY software platforms and AI-powered tools have entered the market at price points 10–30 times lower. This raises an obvious question: does the IRS care who does the study, or is the standard strictly about quality of analysis? The answer matters enormously for investors evaluating their options.

What the IRS Audit Techniques Guide Actually Says

The IRS Cost Segregation Audit Techniques Guide (ATG) is the definitive reference document for what makes a defensible study. The ATG describes eight acceptable study methodologies and does not require that studies be performed by engineers, CPAs, or any specific professional class.

What the ATG does require is that the study be: (1) based on property-specific cost data or engineering estimates, (2) detailed and well-documented with supporting evidence, (3) prepared by someone with knowledge of cost segregation principles and applicable tax law, and (4) consistent with the applicable asset class tables in Rev. Proc. 87-56.

The Spectrum of Study Quality

Why Engineering Studies Aren't Always Necessary

For a large commercial office building or a custom-built hotel, an engineering firm's on-site inspection provides irreplaceable value — the component-level cost estimates require physical verification of systems, finishes, and construction specifics that vary significantly from property to property.

For a residential STR in the $400K–$1.5M range, the component mix is far more standardized. The IRS asset class tables are clear about which residential components qualify as 5-year and 15-year property. A study that applies these rules correctly using property-specific documentation — photos, floor plans, closing documents, improvement invoices — is defensible even without a physical engineering inspection.

The Pure DIY Problem

Where taxpayers get into trouble is attempting to do cost segregation themselves by simply assigning arbitrary percentages to their properties without any methodology. Entering "25% personal property" on a tax form without a supporting study is not a cost segregation study — it's an unsupported estimate that will not survive examination.

The IRS ATG explicitly states that "unsupported percentage estimates" are "the least preferred approach" and that studies relying on them provide minimal audit protection. If challenged, the entire reclassification could be reversed, and the taxpayer would face back taxes plus interest and potentially penalties.

What Makes an AI-Powered Study Defensible

AI-powered cost segregation platforms like Abode produce studies that meet the ATG requirements by doing the same analysis an engineering firm would — at the component level, based on property-specific data, with IRS authority citations — at a dramatically lower cost. The key elements of defensibility are:

• Property-specific analysis: Classifications are based on your actual property's components, not industry averages.
• Asset class citations: Each classification cites the applicable MACRS asset class from Rev. Proc. 87-56 and relevant IRS guidance.
• Documented methodology: The narrative report explains the methodology used, which should align with one of the eight ATG-recognized approaches.
• Complete fixed asset schedule: Every identified asset is listed individually with its basis, recovery period, and depreciation method.

The Cost-Benefit at Different Property Values

Note that the ROI column represents the ratio of additional first-year deductions to study cost — not the tax savings directly. At a 37% marginal rate, $100,000 in additional deductions translates to $37,000 in tax savings. Even at 22%, the savings vastly exceed the study fee.