Structural Components of a Building: Depreciation, Repairs, and QIP

For IRS depreciation purposes, the structural components of a building — walls, floors, ceilings, roofs, windows, doors, HVAC, plumbing, electrical, elevators, sprinklers, and similar infrastructure — are treated as part of the building itself and depreciate over the same recovery period: 27.5 years for residential rental property or 39 years for nonresidential real property. That default is slow, but several provisions let you recover parts of that cost faster, including 100 percent bonus depreciation restored under the One, Big, Beautiful Bill Act signed in July 2025, a 15-year recovery period for qualified improvement property, Section 179 expensing for specific upgrades like roofs and HVAC, and cost segregation studies that reclassify components into shorter-lived categories.

What Counts as a Structural Component

The definition sits in 26 CFR § 1.48-1(e)(2). Structural components are the parts of a building tied to its operation and maintenance: walls, partitions, floors, ceilings, permanent coverings like paneling or tiling, windows, doors, HVAC systems and all their motors, compressors, pipes, and ducts, plumbing and plumbing fixtures, electrical wiring, lighting fixtures, chimneys, stairs, escalators, elevators, sprinkler systems, and fire escapes. The regulation closes with a catch-all covering “other components relating to the operation or maintenance of a building.”1eCFR. 26 CFR 1.48-1(e) – Definition of Section 38 Property

The practical test is whether the item is woven into the building’s physical fabric so that removing it would leave the building unable to function normally. If yes, it loses its separate identity, becomes part of the real estate for tax purposes, and follows the building’s depreciation schedule rather than qualifying for the faster write-offs available to personal property like furniture or equipment.

The regulation also defines what counts as a “building” in the first place: a structure enclosing space within walls, usually with a roof, whose purpose is shelter, housing, or working space. Warehouses, apartment complexes, offices, and retail spaces qualify. Structures that are essentially machinery, like a blast furnace or refinery tower, do not, even if they have walls and a roof.2Government Publishing Office. 26 CFR 1.48-1 – Definition of Section 38 Property

Default Recovery Periods

Under the Modified Accelerated Cost Recovery System, residential rental property depreciates straight-line over 27.5 years. A building qualifies as residential rental if 80 percent or more of its gross rental income comes from dwelling units. Everything else — commercial, warehouse, office, retail — is nonresidential real property and depreciates over 39 years.3Office of the Law Revision Counsel. 26 USC 168 – Accelerated Cost Recovery System

Structural components ride along on whichever schedule applies to their building. A new HVAC system in an apartment complex gets added to the building’s depreciable basis and recovered over 27.5 years. The same system in an office building stretches over 39 years.4Internal Revenue Service. Publication 946 – How To Depreciate Property Either way, you’re spreading the cost across decades rather than deducting it in the year you wrote the check. Those long timelines are mandatory for the shell and any component that stays classified as real property. The rest of this article is about the exceptions.

The Nine Building Systems That Decide Repair vs Improvement

The tangible property regulations finalized in 2013 divide a building into specific “units of property.” Each building has a building structure (the shell) plus eight designated building systems:5eCFR. 26 CFR 1.263(a)-3 – Amounts Paid to Improve Tangible Property

  • HVAC — heating, ventilation, and air conditioning, including boilers, furnaces, chillers, compressors, pipes, ducts, and radiators.
  • Plumbing — pipes, drains, valves, sinks, bathtubs, toilets, and water or sewer equipment running to and from the property line.
  • Electrical — wiring, outlets, junction boxes, lighting fixtures, and connectors.
  • Escalators — all escalator components as a single system.
  • Elevators — all elevator components as a single system.
  • Fire protection and alarm — sprinkler heads and mains, piping, pumps, detectors, alarm panels, fire escapes, fire doors, emergency exit lighting, and firefighting equipment.
  • Security — window and door locks, cameras, recorders, monitors, motion detectors, security lighting, alarm systems, and access controls.
  • Gas distribution — pipes and equipment distributing gas to and from the property line.

This matters because the IRS evaluates improvements at the system level, not the whole-building level. Replace all the ductwork in a commercial building and the question is not whether you improved the entire building but whether you improved the HVAC system. That framing often determines whether your spending is a deductible repair or a capital improvement that must be capitalized and depreciated.

Faster Write-Offs: QIP, Section 179, and Bonus Depreciation

Three provisions do most of the work of getting building spending off the 27.5- or 39-year schedule.

Qualified Improvement Property

Qualified improvement property (QIP) is any improvement to the interior of a nonresidential building that is already in service. It applies whether you own or lease the space, and there is no requirement that the work be done under a lease. Three categories are excluded: building enlargements, elevators and escalators, and changes to the internal structural framework such as load-bearing walls and columns.3Office of the Law Revision Counsel. 26 USC 168 – Accelerated Cost Recovery System

QIP depreciates over 15 years under the general depreciation system instead of the standard 39-year commercial schedule.4Internal Revenue Service. Publication 946 – How To Depreciate Property That shorter life also makes QIP eligible for bonus depreciation. Non-load-bearing partitions, ceiling work, interior flooring, and built-in lighting inside a commercial building all potentially qualify. QIP does not apply to residential rental property; renovations inside an apartment building follow the standard 27.5-year schedule.

Bonus Depreciation

For qualifying assets acquired after January 19, 2025, the One, Big, Beautiful Bill Act (signed July 4, 2025) permanently restores the additional first-year depreciation deduction to 100 percent of the asset’s adjusted basis.6Internal Revenue Service. Notice 2026-11 – Interim Guidance on Additional First Year Depreciation Deduction The full cost is deductible in the year the property is placed in service.

Bonus depreciation applies only to property with a recovery period of 20 years or less. The building shell and most structural components sit at 27.5 or 39 years, so they don’t qualify on their own. Bonus depreciation becomes relevant for building-related spending through two channels: QIP (15 years) and components reclassified through a cost segregation study to 5, 7, or 15 years.

Section 179 Expensing

Section 179 lets you deduct the full cost of qualifying property in the year it’s placed in service, up to an annual dollar cap. For 2026, the cap is approximately $2,560,000, phasing out dollar-for-dollar once total qualifying purchases exceed roughly $4,090,000. The provision covers several categories of real property improvements to nonresidential buildings already in service:7Office of the Law Revision Counsel. 26 USC 179 – Election to Expense Certain Depreciable Business Assets

  • Roofs
  • HVAC property
  • Fire protection and alarm systems
  • Security systems
  • Qualified improvement property

You cannot use Section 179 for a brand-new building or for residential rental property. And unlike bonus depreciation, Section 179 cannot create or increase a net operating loss; the deduction is capped at your taxable income from active trades or businesses for the year.

Section 179 and bonus depreciation are not mutually exclusive. You might expense part of a project under Section 179, claim bonus depreciation on the remainder, and depreciate anything left over the regular MACRS period.

When Spending Counts as a Repair Instead

Not every dollar spent on a building has to be capitalized. The tangible property regulations include two safe harbors that let building owners deduct certain spending immediately.

De Minimis Safe Harbor

With an applicable financial statement (audited financials filed with the SEC, a certified audit report, or statements required by a government agency), you can elect to deduct amounts up to $5,000 per invoice or per item. Without one, the threshold is $2,500.8Internal Revenue Service. Tangible Property Final Regulations The election is made annually on your return and applies to all qualifying expenditures for that year. A $2,400 water heater replacement in a rental unit could be deducted immediately under this election rather than capitalized over 27.5 years.

Routine Maintenance Safe Harbor

Recurring maintenance activities that keep a building in ordinary operating condition can be deducted currently if you reasonably expect to perform them more than once during the first ten years after the building is placed in service. Repainting common areas, servicing HVAC, patching a roof, and cleaning gutters typically qualify.8Internal Revenue Service. Tangible Property Final Regulations The safe harbor does not cover work that makes a building system materially better than it was when originally placed in service; that crosses into an improvement and has to be capitalized regardless of how routine it feels.

The line between a repair and an improvement gets blurry quickly on larger projects. Replacing a few shingles is maintenance. Replacing an entire roof section with upgraded materials looks more like a betterment or restoration, which must be capitalized. The nine building systems are the unit of property against which that judgment gets made.

Cost Segregation Studies

A cost segregation study is an engineering-based analysis that breaks a building’s cost into its individual components and reclassifies as many as possible from the long recovery period to shorter ones. The point is to move spending out of the 27.5- or 39-year bucket and into 5-year, 7-year, or 15-year buckets, where bonus depreciation and faster write-offs apply.

Components commonly reclassified to 5-year property include carpeting and removable flooring, decorative lighting, cabinetry, window treatments, appliances, removable partitions, and dedicated electrical or plumbing lines serving specific equipment rather than the building generally. Land improvements — parking lots, fencing, sidewalks, landscaping, site drainage — typically move to the 15-year category.4Internal Revenue Service. Publication 946 – How To Depreciate Property

With 100 percent bonus depreciation restored for property acquired after January 19, 2025, a cost segregation study on a newly purchased commercial building can generate a substantial first-year deduction. A $3 million office building where $600,000 of components reclassify to 5-year or 15-year property produces a $600,000 deduction in year one instead of spreading that amount over 39 years. Studies can also be done retroactively on buildings you already own, with catch-up depreciation claimed through a change in accounting method in a single year rather than by amending prior returns.

Land Improvements Sit in Their Own Category

Property outside the building’s walls often depreciates on a different schedule. Land improvements — fences, sidewalks, roads, parking lots, landscaping, drainage systems — recover over 15 years under MACRS, not 27.5 or 39.4Internal Revenue Service. Publication 946 – How To Depreciate Property Land itself is never depreciable.

The distinction trips people up because some site-related infrastructure looks similar to building components. Plumbing inside the building is a structural component depreciating with the building. Sewer lines from the building to the property line are part of the plumbing building system. But a paved parking lot next to the building is a 15-year land improvement. The difference between a 15-year and a 39-year recovery matters, especially when bonus depreciation is available for the shorter-lived asset.

When an Item Isn’t on Any List: The Whiteco Test

If an item does not appear on any regulatory list, courts apply a six-factor test from the 1975 Tax Court case Whiteco Industries, Inc. v. Commissioner to decide whether it is a permanent structural component or removable personal property:9Internal Revenue Service. Technical Advice Memorandum 201404001

  • Movability — can it be moved, and has it ever actually been moved?
  • Design intent — was it designed or constructed to remain permanently in place?
  • Expected duration — how long was it intended to stay?
  • Difficulty of removal — how substantial and time-consuming is the removal process?
  • Damage on removal — how much damage will the item or the building sustain?
  • Manner of attachment — how is it physically attached to the land or building?

No single factor decides the question. An item bolted to a concrete pad that could technically be unbolted may still be a structural component if it was designed for that specific location, would suffer significant damage during removal, and was never intended to be relocated. The test appears frequently in cost segregation disputes and IRS audits. Documentation at the time of installation — photographs, engineering specifications, written descriptions of intended use — helps defend a classification if the IRS challenges it later.

Depreciation Recapture When You Sell

Every dollar of depreciation you claim on a building or its structural components creates a potential tax liability at sale. Gain on the sale of depreciable real property splits into two parts. The portion attributable to straight-line depreciation previously claimed, called unrecaptured Section 1250 gain, is taxed at a maximum federal rate of 25 percent rather than the lower long-term capital gains rates. Gain above the total depreciation taken is taxed at standard capital gains rates.

Recapture applies to depreciation on the building itself and on every structural component included in the building’s depreciable basis. Accelerating deductions through bonus depreciation, Section 179, or a cost segregation study doesn’t change the recapture rate; it just means the recapture amount is larger because the deductions were larger. Owners planning to hold property long-term often accept that trade because the time value of money favors taking bigger deductions now and paying the recapture years later at sale.