A commercial building goes on the books as one number. The closing statement says land, and it says building, and the building line starts depreciating over 39 years.
Inside that one number sits the parking lot. The sidewalks and the perimeter fence sit there too. So does the carpet, the decorative lighting, and the branch circuit feeding the walk-in cooler. None of those items lasts 39 years, and federal tax law does not require an owner to depreciate them as though they did.
A cost segregation study is the engineering and tax exercise that pulls those items back out. This post explains what it moves, who qualifies, how the catch-up works for a building already on the books, and how to tell a serious study from a cover page.
Stone Path Consulting is not a CPA firm and does not give tax advice. Every figure below traces to a published IRS source. The sentence that uses a figure names the publication it came from. Your CPA confirms how any of it applies to your return.
What a cost segregation study actually does
The IRS explains the exercise in its own words. The Cost Segregation Audit Techniques Guide, IRS Publication 5653, describes the analysis this way: property "often consists of numerous asset types with different recovery periods," and when only lump-sum costs exist, "cost estimating techniques may be required to 'segregate' or 'allocate' costs to individual assets or items of property."
The split that matters is a legal one. The same guide states that a building is "section 1250 property," which is generally nonresidential real property with a 39-year recovery period or residential rental property with a 27.5-year recovery period. Equipment, furniture, and fixtures are "section 1245 property," which the guide describes as tangible personal property carrying "a shorter recovery period (e.g., 5 or 7 years)."
The guide states the consequence plainly: "a faster depreciation write-off (and tax benefit) can be obtained by allocating costs to section 1245 property."
That is the whole idea. A study does not create a deduction. It reclassifies costs the owner already paid onto the recovery periods those costs actually belong on.
The four lines a building splits into
Under the general depreciation system, most commercial property lands on one of four lines.
| What it is | Recovery period | IRS source |
|---|---|---|
| Nonresidential real property (the building shell) | 39 years | Pub 5653, citing IRC 168(c) |
| Residential rental property | 27.5 years | Pub 5653, citing IRC 168(c) |
| Land improvements, Asset Class 00.3 | 15 years | Pub 5653, citing Rev. Proc. 87-56 |
| Tangible personal property, Asset Class 57.0 | 5 or 7 years | Pub 5653 |
Land itself never depreciates, and a study allocates land value first.
The 15-year line is the one most owners have never looked at. Publication 5653 describes Asset Class 00.3 land improvements as "depreciable improvements made directly to or added to land," and its examples include sidewalks, roads, canals, waterways, drainage facilities, sewers, wharves, docks, bridges, fences, landscaping, and shrubbery.
Read that list against your own property. Almost every commercial site has several of those items, and almost every closing statement buried all of them in the building line.
The check: pull the depreciation schedule your accountant files with the return. Count how many separate asset lines exist for the property. One line for land and one for building means nothing has ever been segregated, and the parking lot is sitting at 39 years.
What ends up on the shorter lines
Two categories move.
Site work moves to the 15-year line. Parking areas, striping, curb work, perimeter fencing, exterior lighting, drainage, and landscaping all live in Asset Class 00.3 when they serve the site generally. Publication 5653 adds one wrinkle for manufacturers: land improvements tied directly to a production process can fall into that industry's own asset class and carry a different life.
Interior items move to the 5-year or 7-year line when they qualify as tangible personal property. Publication 5653 names the everyday candidates directly: "carpeting, wall coverings, partitions, millwork, and lighting fixtures." It also warns that these "may or may not constitute section 1245 property depending on the particular facts and circumstances for which the project was designed."
The electrical system is where a study earns or loses its credibility. The IRS guide describes the accepted method: a study identifies the branch circuits feeding section 1245 equipment and classifies them at the equipment's recovery period, and it may allocate a percentage of the building's electrical distribution system to section 1245 based on the load that system carries. The guide gives 15 percent of the distribution system supporting specialized kitchen equipment as its example, and it adds a caution worth repeating: "the allocation of building components to section 1245 property is often a contentious issue."
The legal footing for all of this is a Tax Court decision. Publication 5653 describes Hospital Corporation of America, 109 T.C. 21 (1997), as "a landmark decision" in which the court ruled that tangible personal property included in an acquisition "should be treated as such for depreciation purposes." The IRS acquiesced to the use of investment tax credit rules for telling section 1245 property from section 1250 property.
Who qualifies for a study
Four conditions carry most of the answer, and none of them depends on the size of the company.
You need depreciable real property used in a trade or business or held to produce income. You need a cost basis in that property, from purchase, construction, or improvement. You need taxable income the deduction can reduce, now or through a carryforward your CPA calculates. And you need enough basis on the building line for the reclassification to be worth the fee.
Owners who commonly qualify include buyers of an existing commercial building, developers finishing new construction, and owners who completed a renovation or a tenant buildout. The trigger event is a purchase, a build, or an improvement that put a lump sum on the books.
Publication 5653 also draws a line at leased space. A tenant's improvements to leased property follow their own rules, and the guide devotes separate treatment to qualified improvement property. Ask your CPA which set applies before assuming either.
The building you already own, and the catch-up
Most owners hear about cost segregation years after the purchase. The deduction is not lost, and the way to claim it surprises people.
You do not amend the old returns. Publication 5653 is explicit: it is the position of the IRS that a change in the depreciation method, recovery period, or convention resulting from reclassification "is a change in accounting method," and that change "requires the consent of the Commissioner (i.e., the taxpayer must generally file a Form 3115, Application for Change in Accounting Method)."
The guide then says what happens to the missed depreciation: "the adjustment to taxable income is made pursuant to section 481(a)." It also states the negative directly. Claims based on a study performed after the original return was filed "should not be allowed" through amendment, and the taxpayer should instead use the voluntary method change procedures in Rev. Proc. 2015-13 by filing a Form 3115.
In practice that means the depreciation an owner missed across prior years arrives as a single adjustment in the year of the change. The IRS guide lists the failures it sees most in this area, and two of them belong to the owner rather than the preparer: "Form 3115 is not filed" and "lack of records to substantiate the section 481(a) adjustment."
The check: ask any provider quoting you a look-back study to name the form and the code section in writing. A provider who says "we will amend your returns" has described a route the IRS guide says examiners should reject.
Bonus depreciation, and why the date matters
Property on the shorter lines can be eligible for the special depreciation allowance under IRC 168(k), which most people call bonus depreciation. Eligibility turns on the property's recovery period and on its dates, and your CPA confirms both against the current rules. That eligibility is what turns the 5-year and 15-year lines into cash in the first year.
The percentage has moved repeatedly, and the date the property was acquired and placed in service controls it. IRS Publication 946, the 2025 edition, states a 100 percent special depreciation allowance for certain qualified property acquired and placed in service after January 19, 2025, with an election available to take 40 percent instead. The same publication states that for most qualified property acquired before January 20, 2025, the allowance is limited to 40 percent.
Two dates decide your number, and both belong to your property. The calendar year you happen to be reading in settles nothing. Ask your CPA to confirm the acquisition date and the placed-in-service date on the record before anybody models a benefit.
What the study costs you later
A study accelerates deductions. It does not erase them, and the day you sell, the split you created has consequences.
IRS Publication 544, the 2025 edition, sets out the difference. For section 1245 property, the depreciation deducted on the property is recaptured as ordinary income up to the amount of the gain. For section 1250 property, only the additional depreciation above what straight-line would have allowed is recaptured as ordinary income.
Moving costs from the 39-year line to the 5-year line therefore moves them into the harsher recapture rule. For an owner who intends to hold the property or to exchange it, the timing benefit usually wins. For an owner planning to sell in three years, the math is a real question and it belongs in front of a CPA before the study is commissioned.
State treatment adds a second question. States set their own conformity with federal bonus depreciation, and the state answer can differ from the federal one. Ask your preparer what your state does before you count the federal number as the whole benefit.
What separates a real study from a cover page
The IRS wrote down what it wants to see, which makes vetting a provider easier than most purchasing decisions.
Publication 5653 lists 13 principal elements of a quality study. Among them: preparation by an individual with expertise and experience, a detailed description of the methodology, use of appropriate documentation, interviews conducted with appropriate parties, an explanation of the legal analysis, determination of unit costs and engineering take-off, reconciliation of total allocated costs to total actual costs, an explanation of the treatment of indirect costs, and identification and listing of section 1245 property.
The guide also says something that should change how you shop. "There are no prescribed qualifications for cost segregation preparers." It adds that "in general, a study by a construction engineer is more reliable than one conducted by someone with no engineering or construction background," and that a quality study "identifies the preparer and always references their credentials, experience, and expertise."
For an acquired building, the guide adds one more requirement. A quality study "documents how the purchase price was allocated between land, land improvements, building and other assets," and "land value is always determined first and is based on highest and best use."
The check: ask the provider for a sample report on a property like yours, with the client details removed. Look for the reconciliation to total actual cost, the preparer's credentials, and the legal analysis. A report that lists asset totals with no reconciliation and no legal reasoning is a spreadsheet, and it will not survive the examination the IRS guide describes.
Getting a study scoped
Stone Path Consulting works as a strategic facilitator. It reads what a property owner is holding and connects that owner with a vetted cost segregation provider. Stone Path does not perform the study, does not prepare returns, and does not give tax advice. The provider bills the client directly.
Ty Woods runs the firm and takes the calls. Stone Path charges nothing for a consultation and nothing for a referral.
Older background on the topic sits in Stone Path's earlier piece on cost segregation in real estate and in its overview of real estate depreciation. Owners holding rental housing should also read the rental tax savings piece, because the base recovery period and several of the interior line items change once dwelling units are involved. Apartment cost segregation covers that case in full, including the clubhouse and the detached parking structure that stay at 39 years.
Stone Path works with businesses across Arkansas and nationally. Use the contact page and say what the property is, when you acquired or built it, and what your depreciation schedule currently shows. Bring your CPA into that conversation early, because the CPA files the Form 3115 and owns the position on the return.