A measured reference on what the IRS actually evaluates in a cost segregation studyA study that reclassifies portions of a building's basis into shorter-life property (5, 7, or 15-year) so it depreciates faster.. What matters in practice, where defensibilityDefensibility is the property of a study that allows it to survive examination — methodology, documentation, and consistency with the regulations. actually comes from, and where the risk patterns sit.
The audit base rate for the relevant filings is small. The question that determines the outcome is not will this get audited — it is if it does, what holds up? Methodology and documentation hold up. Brand and price are not part of the examination.
Most of the public worry about cost segregation is about the wrong variable. The thing that turns a study into a problem is rarely the existence of the study — it is the §469 posture§469 governs passive activity losses. Cost-seg losses applied against W-2 wages without material participation or REPS qualification is the most common downstream failure mode. on the return that uses it.
Engineering firms and independent providers follow the same federal guidance. The variation between competent shops is operational — turnaround, documentation format, revision behavior — rather than methodological.
For a typical residential property, two competent studies usually fall within a few percentage points of each other on reclassified basis. The buyer's decision is being made on operational terrain, even when the marketing suggests otherwise.
A subset of providers has standardized the residential study workflow into software. The methodology is unchanged from the engineering tradition. Operational consistency tends to be higher because the steps are the same on every file.
The trade-off is straightforward. Standardization tends to lower price and improve consistency of documentation. It is less appropriate for unusual properties — large mixed-use, ground-up construction, anything where on-site engineering judgment materially changes the schedule.
Hypothetical, for illustration. Numbers rounded.
A short checklist. Answer based on what you actually have in the binder, not what was promised.
Yes — when the study follows IRS Audit Technique Guide methodology (Pub. 5653), uses qualified-engineer reclassification per Rev. Proc. 87-56, and matches §1.263(a) capitalization rules. The audit base rate for cost-seg studies is roughly 0.4%, in line with general individual-return audit rates. Risk concentrates in aggressive class lives, §469 W-2 offset without REPS or STR qualification, and estimated-only studies missing site evidence.
The IRS Cost Segregation Audit Techniques Guide (Pub. 5653) defines 13 quality elements an examiner evaluates: methodology, documentation, site evidence, component-level basis, classification rationale per asset class, consistency with §1.263(a), and engineer attestation. Methodology and documentation account for the majority of the examination weight; provider brand and price paid are not part of the evaluation.
Roughly 0.4%, in line with the general individual-return audit rate. The IRS does not publish cost-segregation-specific examination data; this estimate is derived from published individual-return audit rates plus practitioner interviews. The base rate is small enough that the relevant question is not whether a study will be audited but whether it holds up if examined.
Three patterns concentrate examination risk: aggressive asset-class lives that don't match Rev. Proc. 87-56; §469 W-2 offset claimed without Real Estate Professional Status (REPS) or the §469(c)(7) STR exception (7-day average rule); and estimated-only studies that lack the site evidence and component-level workpapers an examiner expects from an engineering-based study.
It increases scrutiny if the §469 posture isn't defensible. Cost-seg losses applied against W-2 wages without material participation (100+ hours, more than anyone else) and without either REPS qualification or the STR 7-day average exception is the most common downstream failure mode. The strategy is sound when §469 qualification is documented; it fails when the documentation isn't there.
For complex commercial properties above ~$5M, a physical site visit is typical and expected. For residential, short-term rental, and small-commercial properties, public records, satellite imagery, and a structured property questionnaire produce defensible site evidence — provided the workpapers explicitly document data sources and component-level basis. The IRS ATG does not mandate physical site visits for all property types.
IRS Publication 5653, the Cost Segregation Audit Techniques Guide (ATG), is the canonical IRS document defining the methodology, evidentiary standards, and 13 quality-control elements an examiner uses to evaluate a cost segregation study. Every defensible study is structured around the ATG's framework: §1.263(a) capitalization rules, MACRS classification per Rev. Proc. 87-56, and the documentation each component requires.
Every methodology and audit-defensibility claim on this page is grounded in the IRS primary sources below. These are the documents an examiner references during a cost-segregation examination.