Partial Asset Disposition: Deduct the Parts You Replace

Buy a building and its roof, HVAC and windows are all inside one number on your depreciation schedule. Replace one of them years later, and unless you do something about it, the cost of the part you hauled away keeps depreciating for decades next to the new one.

This guide is educational, not individualized tax advice. The election and the cost estimate depend on your records and the property.

The election treats the removed component as disposed of. You deduct its remaining adjusted basis, its original cost less the depreciation taken on it, as a loss in the year of the replacement. The new component is capitalized and depreciated on its own schedule.

• Elective for ordinary replacements you choose to make, such as a roof, HVAC unit, windows or interior finishes.
• Required in some cases, such as a part lost in a casualty or a portion of the asset that you sell.
• Made on time by reporting the loss on the timely filed original return, including extensions, for the year of the disposition. No separate form is needed for that timely election, and a late election is allowed only in narrow cases, such as when an IRS exam reclassifies a repair as a capitalized replacement.

A business owner bought an office building in 2018. In 2026 the original rooftop HVAC system is replaced. A reasonable estimate puts the original system's share of the building cost at $40,000. After eight years on a 39-year schedule, about $8,205 of it has been depreciated, so roughly $31,795 remains.

Illustrative example, not a client result. The new system is capitalized either way. On nonresidential property, HVAC added after the building was placed in service can be Section 179 qualified real property, so the replacement itself may be expensed too; a roof replacement works the same way.

You rarely have an invoice for a roof or HVAC system that came with the building. When your records cannot show its cost, the regulations allow any reasonable method you apply consistently, and list examples:

• Producer Price Index: discount the cost of the new part back to the year the building was placed in service, available when the new part is a like-for-like replacement rather than an upgrade.
• Pro rata replacement cost: allocate the building's cost in proportion to what each part would cost to replace.
• A cost segregation study: a study that already assigned cost to each component makes every later replacement easy to support.

• Missing the return: the timely election lives on the original return for the year of replacement. Decide before you file.
• Loss plus repair: if you deduct a loss on the removed part, its replacement must be capitalized; it cannot also be deducted as a repair.
• Removal costs: the cost of tearing out the old part can generally be deducted when you take the partial disposition, instead of being added to the new part.
• Interior work on commercial buildings: the replacement may be qualified improvement property with a 15-year life and bonus depreciation.