How Does Cost Segregation Work After a Renovation?

Two separate moves, one tax year

A renovation or capital improvement is where cost segregation does more than one thing at once, and it is easy to only see half of it. Half the opportunity is obvious: new construction cost was just spent, and that new cost, new flooring, a new roof, new HVAC equipment, new lighting, gets its own component-level classification into 5-year, 7-year, and 15-year recovery periods, the same way an original building purchase would.

The other half is easy to miss entirely: whatever the renovation replaced still has undepreciated basis sitting on the books. Under the partial asset disposition rules (Treas. Reg. 1.168(i)-8), that remaining basis of the OLD component can be written off in full, in addition to classifying the new one. Doing only the first half and missing the second half leaves real money on the table.

Move one: classifying the new work

The engineering behind classifying a renovation is identical to classifying an original purchase. New cabinetry, decorative lighting, and certain electrical or plumbing serving equipment fall into the 5-year bucket. New paving, fencing, landscaping, or outdoor lighting falls into the 15-year land improvements bucket. Structural work, including a new roof structure or a building's central HVAC system, generally stays on the 39-year (commercial) or 27.5-year (residential) structural schedule, a common misconception is that a roof or central HVAC qualifies as 5-year property; it does not.

Those newly classified components generally qualify for bonus depreciation at the rate tied to when the renovation itself was placed in service, which for renovations completed after January 19, 2025 means 100% bonus under the 2025 One Big Beautiful Bill Act.

Move two: the partial asset disposition election

This is the move that gets missed. When a roof is torn off and replaced, or an HVAC system is swapped out, the old component's remaining, undepreciated basis does not automatically disappear from the books just because it was physically removed. Without a partial asset disposition election, that old roof or old HVAC system keeps depreciating on its original 39-year or 27.5-year schedule for decades, stacked right alongside the new one, effectively depreciating two roofs at once on paper for a building that only has one.

The election lets the owner write off that old remaining basis entirely, but the regulation is specific: it has to be claimed in the tax year the replacement happens. There is no going back to claim it on a later year's return once that tax year closes. Full detail on how this election works lives on the partial asset disposition page.

What the combined move can look like

A study following that path against a restaurant renovation, for example, can move a meaningful share of basis into faster schedules; the benchmark studies our engineering team has delivered on restaurant properties run toward the high end of the 15 to 35% typical range for basis shifted into faster recovery periods, since restaurants carry a heavy concentration of finish work exactly like a renovation would add.

A third mechanic on nonresidential renovations: section 179

On nonresidential commercial property, a renovation that replaces the roof, HVAC, fire protection or alarm systems, or security systems can qualify for section 179 expensing under the qualified real property rules, on top of the classification and disposition moves already described. Section 179 lets that cost be expensed rather than depreciated over time, subject to the annual dollar limits and to the taxpayer's business income for the year. This does not apply to residential rentals, only nonresidential property, but for an owner replacing a roof or HVAC system on a commercial building, it is a third lever sitting alongside the standard classification and the disposition election, not a substitute for either one.

Why the invoices need to be tracked as the work happens

The classification move and the disposition election both depend on records that are easiest to gather while the renovation is happening, not after the fact. Contractor invoices broken out by scope of work, the specific date the old component was removed, and photographs of both the old and new work all make the eventual engineering cleaner and faster. A renovation studied years after completion can still be classified, but reconstructing exactly what was replaced and when becomes harder the longer it waits, particularly for the disposition election, which depends on pinning down the precise tax year of the replacement.

Timing the study around the renovation

Because the disposition election is same-year only, the practical guidance is straightforward: if a renovation involving a component replacement is happening this year, the study needs to happen this year too, or at least the disposition election needs to be identified and claimed before the return for this year is filed. A renovation completed and studied in the same tax year captures both moves cleanly. A renovation studied years later can still capture the new construction cost through ordinary classification, but the old component's disposition election is already gone if that year has closed.

Frequently asked questions

Do I need a separate study for the renovation, or does it fold into the original building study?

It can be handled either way depending on timing, but the engineering treats the renovation's new components as their own classification project layered on top of whatever the original building study identified. If no original study exists yet, both can be done together.

What if I already filed the return for the year I replaced my roof?

The partial asset disposition election for that specific roof replacement generally cannot be claimed on a later return once that tax year has closed. The rest of the building, and any newer renovation components, can still be classified normally going forward.

Does a small renovation, like new flooring in one unit, qualify for this treatment?

The same classification principles apply regardless of renovation size; the question is whether the scope and cost justify an engineered study relative to the deduction it would identify. A free Preliminary Benefit Estimate answers that for a specific project before any commitment.

Is the roof itself ever 5-year property after a renovation?

No. A structural roof and a building's central HVAC system are structural components, staying on the 39-year (commercial) or 27.5-year (residential) schedule, whether original or replaced. That is a common misconception this page corrects directly.