Site Inspections: Documentation, Methodology & Audit Defensibility

Executive Summary

A cost segregation study identifies the components of a building that qualify as 5-, 7-, or 15-year property and separates their cost from the 39-year (nonresidential) or 27.5-year (residential rental) building. The result is a faster depreciation schedule. But the schedule is only the output. What supports it is the methodology, the preparer’s qualifications, the source records, the cost-allocation process, the classification analysis, and the documentation behind every number.

Bonus depreciation puts the deduction on the first return. Bonus depreciation is not new. Under the Tax Cuts and Jobs Act the rate was 100% for qualified property acquired and placed in service after September 27, 2017 through 2022, then phased down to 80% in 2023, 60% in 2024, and 40% in 2025. Public Law 119-21 (July 4, 2025) restored the 100% rate and made it permanent for qualified property acquired after January 19, 2025; property acquired on or before that date stays on the phase-down schedule, with the rate set by the year it is placed in service. Property a study reclassifies into 5-, 7-, or 15-year classes is generally eligible, so a large share of the reclassified cost, and at the 100% rate all of it, is deducted in the year the property is placed in service rather than over decades. Whichever rate applies, the classification evidence carries that deduction on the first return.

The IRS has told examiners what to look for. The Cost Segregation Audit Technique Guide (Publication 5653, revised February 2025) is written for IRS examiners. The IRS describes its purpose as providing examination steps that “facilitate the audit process and minimize burden on taxpayers, practitioners, and Service examiners alike.” It is not law, and it says so. It matters because it lists the elements the IRS associates with a quality study and the questions an examiner will ask, including whether the preparer conducted a site visit.

On field work, the ATG is direct. Chapter 3 states that “a field inspection is recommended for all quality studies, whether the studies are for new or used properties,” and that when drawings and specifications are limited or unavailable, which is often the case for acquired property, “field inspection of the property is a critical step.” Chapter 4 states that a quality study includes a site visit.

What this means for you

Inspection Approaches: Relative Evidentiary Strength

Providers establish physical facts in different ways, and the right approach depends on the property, the records available, the scope of the study, the materiality of the deductions, and the complexity of the classifications. The comparison below is about evidentiary quality, not price.

The practical difference is not the number of photographs

A large photo set is not a strong inspection record. The value of field work lies in whether it captures the facts the study needs: what the asset is, what it serves, how much of it exists, how the quantity was determined, and how the observation feeds the cost allocation and classification. A useful field record answers those questions asset by asset.

Where Field Work Matters Most

Acquired properties

Acquisition studies usually reconstruct component costs because the original construction records are gone. The inspection becomes a primary source: identifying installed components, developing quantities, separating land improvements from the building and from non-depreciable land, and determining whether specialized systems serve the building generally or a particular business function. For the CPA: this is the study most likely to rest on estimated costs, so the field record is what you will be asked to produce.

Acquisition plus renovation

When renovation follows an acquisition, the inspection also establishes what existed before the work, what was removed, and what stayed in service. Those facts drive the partial disposition analysis and keep the same basis from being depreciated twice. Timing matters: the partial disposition election is generally made on the timely filed return for the year of the disposition, so the evidence of what came out has to exist before demolition. Interior improvements to a nonresidential building may also be qualified improvement property (15-year, bonus-eligible); the inspection is where that work is distinguished from the structural components and personal property around it.

Look-back studies on property already in service

A study on property placed in service in an earlier year is implemented through a change in accounting method, with a § 481(a) adjustment that brings the depreciation not previously claimed into the year of change. The inspection then has to establish conditions as of the original placed-in-service date and separate everything that has changed since, which gets harder with every year and every renovation. For the owner: the records you kept, or did not keep, from the original construction or purchase set the ceiling on what the study can support.

New construction

New construction usually starts with stronger source records: contractor pay applications, detailed cost ledgers, change orders, specifications, and drawings. The inspection then validates that installed conditions match the design documents, identifies scope changes, confirms materials and quantities, and resolves cost codes that mix building and non-building work.

Properties with specialized systems

Manufacturing, healthcare, hospitality, life-science, data-intensive, entertainment, and other specialized facilities contain systems that serve both general building operation and specific business processes. Classification of these mixed-function systems turns on what the system serves and how it is integrated into the facility, so the factual record has to be specific: which equipment, which loads, which spaces.

Provider Selection: Questions for Owners and CPAs

Evaluate a provider’s inspection model as part of its overall methodology. These questions get further than asking whether a provider “does site visits.”

• Who will perform the field work, and what cost segregation and construction experience does that person have?
• What will be measured, photographed, or documented on site?
• How are field notes and photographs tied to the final asset schedule?
• When actual construction costs are unavailable, how are estimated costs developed and reconciled to basis?
• How does the preparer document mixed-use MEP systems and other assets whose treatment depends on functional use?
• How are renovations, removed assets, and potential partial dispositions identified and documented?
• What quality-control review occurs between the field inspection and the final report?
• Will the provider explain its methodology and provide supporting workpapers if the study is examined?
• Who responds if the taxpayer or the CPA receives an IRS information request, and on what terms?
• Does the engagement letter define scope, assumptions, records required, and examination-support responsibilities?

A more useful way to compare providers

How Green Summit approaches field verification

Green Summit is a licensed engineering firm, founded in 2014, with CPAs and leadership that has performed cost segregation studies since 2001. We provide engineering-based cost segregation and related fixed-asset advisory services, and we work as a consulting partner to CPA firms and building owners. On a Green Summit engagement, that means:

• Field work scoped to the property and its records, performed by personnel who understand the study’s classification and cost-development objectives.
• Measurements, photographs, and notes cross-referenced to the asset schedule, so every quantity and classification has a location and a source.
• Actual costs where they exist, recognized estimating methods where they do not, and a reconciliation to depreciable basis.
• Audit-ready workpapers, and coordination with your CPA from scoping through filing.