Short answer
A cost segregation study is only as strong as the file behind it. The study has to prove three things with documents: what the total cost was and how it splits between land and everything else; what is physically there and how it was built; and what each identified item cost, from records where they exist or from a documented estimate where they do not. The IRS's Audit Techniques Guide lists appropriate documentation, interviews, unit costs and take-offs, an organized asset list and reconciliation to actual costs among the elements of a quality study, and tells examiners to request the complete study, the workpapers, the construction documents and the preparer's qualifications. This article walks through the documents in the order a practitioner uses them, explains what each proves, and says what to do when one is missing. It is general education, not tax advice.
The three questions the evidence must answer
- What did it cost, and what part of that is land? Basis is generally the cost of the property, including certain settlement costs, and when land and buildings are bought together the basis is allocated between them by their fair market values at the time of purchase. Land is never depreciated, so this split comes first and every later number depends on it.
- What is there? The building, its systems, the site improvements and the personal property have to be identified before they can be classified. Drawings, contracts and a site visit answer this.
- What did each part cost? Actual records answer this most reliably. Where they are missing, a documented estimating method fills the gap and says so.
The Audit Techniques Guide describes approaches from a detailed engineering approach based on actual cost records, through engineering estimates when records are unavailable, down to rule-of-thumb approaches that it treats as the least reliable. The evidence you can supply decides which approach is available.
Documents, in the order they are used
| Document | What it proves | If it is missing |
|---|---|---|
| Closing statement or settlement statement | Total purchase price, settlement costs that enter basis, items the seller conveyed | Obtain it from the closing agent or lender; without it the basis itself is unsupported |
| Purchase agreement and any personal-property schedule | What was included in the price; any stated allocation between land, building and personal property | Ask the broker or attorney; an agreed allocation is evidence but not the last word |
| Appraisal | Land value, building description, condition, site improvements, sometimes a cost approach with component values | A separate land valuation or the assessor's allocation, documented and explained |
| Property tax assessment | The assessor's land and improvement values, often used as one input to the land split | Available from the county in most places |
| Construction contracts, change orders and pay applications | Actual cost of construction or renovation by trade and by line item | Estimate from drawings and a cost-estimating method, and disclose that records were unavailable |
| Contractor and supplier invoices | Actual cost of specific items: appliances, flooring, fixtures, site work | Estimate and disclose; keep the request for records on file |
| Architectural, structural, mechanical, electrical, plumbing and site drawings | What was built, quantities, systems and their routing; the basis for take-offs | Measure and document on site; photographs and field notes substitute for drawings on older buildings |
| Specifications and finish schedules | Materials and grades, which drive unit costs | Field observation, documented |
| Permits and certificates of occupancy | When work was completed and the building could be used, which bears on the placed-in-service date | Municipal records; lease or listing dates as supporting evidence |
| Prior depreciation schedules and fixed-asset ledger | How the property has been depreciated so far, which matters for an existing building and for reconciliation | Reconstruct from prior returns with the tax adviser |
| Prior cost segregation study, if any | What was already reclassified; avoids double counting | Not required, but ask the previous owner |
| Leases, rent rolls and listings | Use of the building, which bears on residential versus nonresidential treatment and on the placed-in-service date | Owner records |
| Photographs and site visit notes | What is actually there, its condition, and evidence for items no drawing shows | A site visit is the practitioner's job; if none is made, the report should say why |
Why the site visit matters
Drawings show what was designed. Invoices show what was billed. Neither shows what is in the building today. A site visit confirms that the components exist, records their condition and quantity, finds items the paper does not mention, and produces the photographs that tie the asset list to reality. The Audit Techniques Guide lists documentation and interviews among the elements of a quality study, and the interview with the owner, the manager or the contractor is often where the practitioner learns which equipment serves a business function and which serves the building. A study without a site visit on a property that warranted one should explain the omission and its effect on reliability.
When records are missing
Missing records are normal, particularly for older buildings and for properties bought from an owner who kept little. The rule is not "no records, no study"; it is "no records, say so and estimate properly."
- Request first. Ask the seller, the contractor, the architect, the lender and the municipality. Keep the requests and the answers in the file.
- Estimate second. Where an item's cost is unsupported, the practitioner estimates it from measured quantities and a documented cost source appropriate to the location and date, and records the method. The Audit Techniques Guide describes engineering cost estimates as an accepted approach when actual records are unavailable.
- Disclose always. The report states which costs are from records and which are estimates, and how the estimates were made. Hiding an estimate inside a table of "actual" numbers is the single most damaging thing a study can do to its own credibility.
- Reconcile regardless. Whether costs are actual or estimated, the allocated total must tie to the basis. If estimated components exceed the known total, the estimates are wrong, and the reconciliation is where that is found.
Two dates the file must fix
The acquisition date is when you took ownership; the placed-in-service date is when the property was ready and available for its intended use. Depreciation begins at the placed-in-service date, and bonus depreciation rules turn on when property was acquired. The closing statement, the deed, permits, certificates of occupancy, leases and listings are the evidence. A renovation between purchase and first rental can move the placed-in-service date and separates the renovation costs from the purchase basis. A separate article covers the distinction; the point here is that the file has to contain the documents that fix both dates.
What the finished file looks like
A well-evidenced study has a workpaper file that a reviewer or an examiner can follow from the closing statement to the final asset list:
- The basis and its land split, with the documents and the reasoning.
- The document index: everything received, everything requested and not received.
- The site visit record: date, who attended, photographs keyed to the asset list.
- Take-offs and quantities, keyed to drawings or field measurements.
- Unit costs with their source, marked actual or estimated.
- The asset list, classified, with the legal reasoning for each class.
- The reconciliation to basis and the treatment of indirect costs.
- The report, with methodology, assumptions and limitations.
The Audit Techniques Guide tells examiners to request the complete study, the workpapers, the construction documents and the preparer's qualifications. Building the file this way means those requests can be met from the file itself.
Keep it
Basis records must be kept for as long as they are needed to figure the basis of the original or a replacement property, which for a building means the whole time you own it and through the period after sale when the return can still be examined. Keep the study, its workpapers, the engagement letter and the source documents together, in a form your tax adviser can open years from now.
What people ask on Reddit and other forums
The searches that lead people to these threads are usually phrased "documents needed for a cost segregation study", "cost segregation checklist".
Owners in the "cost segregation reddit" threads on r/realestateinvesting often ask what they will have to dig out of the closing folder. From the sources below:
"I only have the closing statement and the address. Enough?" Enough to start, not enough to finish. A practitioner who asks for nothing else is not preparing the kind of study the IRS describes. Expect requests for the appraisal, any drawings, invoices for appliances and site work, and the prior depreciation schedule.
"The seller kept no records. Can a study still be done?" Yes. Records are requested first; where they do not exist, components are measured and priced with a documented estimating method, and the report says so.
"Do they really need to visit?" For most properties that warrant a study, a site visit is how the practitioner confirms what is there. If no visit is made, the report should say why.
"How long do I keep all this?" As long as you own the property and through the period after sale when the return can be examined.
Questions people also ask
What is the single most important document?
The closing statement, because everything reconciles to it. Second is whatever separates land from building, because land is never depreciated and the split changes every later number.
Do I need drawings for an older house?
Drawings help but are often unavailable. A site visit with measurements, photographs and field notes substitutes, and the report should say that is what was done.
Can the practitioner work from photographs I send?
Photographs are evidence, not a substitute for the practitioner's own inspection where one is warranted. Ask how the practitioner will confirm what is there and why they consider that sufficient for your property.
Is the assessor's land value enough to separate land?
It is one input. Basis between land and building is allocated by fair market value at purchase, and the appraisal, the purchase agreement and market evidence all bear on that. The report should explain what was used and why.
What if the seller gave me a prior study?
Give it to the practitioner and your adviser. It is evidence of what is there and what was previously reclassified; it does not set your basis or your dates.
Sources
- https://www.irs.gov/pub/irs-pdf/p5653.pdf — IRS Publication 5653, Cost Segregation Audit Techniques Guide (Rev. 2-2025): Chapters 3, 4 and 5.
- https://www.irs.gov/publications/p551 — IRS Publication 551 (Rev. December 2024), Basis of Assets: cost basis, real property, allocating the basis, keeping records.
- https://www.irs.gov/publications/p527 — IRS Publication 527 (2025), Residential Rental Property: Chapter 2, Depreciation of Rental Property.
- https://www.irs.gov/publications/p946 — IRS Publication 946 (2025), How To Depreciate Property: Chapter 1, Placed in Service.