What a professional engineered study involves
An engineered cost segregation study is performed by a qualified engineer or specialist firm who physically inspects the property, reviews construction documents and contractor invoices, and produces a detailed report allocating each component to its correct MACRS asset class with supporting documentation. This is the most defensible approach under IRS examination and is typically required for large commercial properties or aggressive bonus depreciation positions.
Rule-of-thumb and self-prepared approaches
Some investors and accountants estimate reclassifiable components using industry average percentages or published cost breakdowns without a physical inspection. This is faster and less expensive but is less precise and carries more audit risk. It may be reasonable for smaller residential rentals where the tax at stake does not justify a study fee, but it still requires a 'reasonable method' — pure guesswork does not meet the standard. Any self-prepared analysis should be supported by contractor invoices or cost allocations.
IRS guidance on what passes audit review
The IRS Cost Segregation Audit Techniques Guide (a public document) describes what examiners look for in evaluating a study. Engineered studies with physical inspections, detailed component lists, and clear documentation pass scrutiny most reliably. For properties where the potential first-year benefit exceeds $30,000, most CPAs recommend a professional study. For smaller properties, discuss with your tax advisor whether a professional study or a well-documented self-analysis is appropriate given the numbers.
Frequently asked questions
Do I need an engineer for a cost segregation study?
Not legally required, but a professional engineered study is more defensible under IRS audit. For large properties or aggressive bonus depreciation positions, it is strongly recommended.
How much does a professional cost segregation study cost?
Typically $5,000-$15,000 for residential properties; higher for large commercial. See our cost guide for details.
Sources
Educational information and estimates only. Not tax advice. Tax rules change and vary by situation; consult a qualified tax professional before acting.