A partial asset disposition lets you deduct the remaining basis of building components you rip out during a renovation, the old roof, the original HVAC, dated windows, in the year you retire them, instead of depreciating ghosts for decades. The election lives in Reg 1.168(i)-8(d)(2) of the tangible property regulations.
The problem it solves
Replace a roof without the election and two things happen: you capitalize the new roof and depreciate it over 27.5 or 39 years, and you keep depreciating the old roof that no longer exists, because its cost is buried in the building's basis. At sale, the phantom roof's accumulated straight-line depreciation still feeds the unrecaptured section 1250 layer taxed at up to 25 percent. The election ends this. The old component is treated as disposed of, its remaining adjusted basis becomes a loss deduction now, and the basis you wrote off can never be recaptured later.
A quick example
A building purchased 4 years ago has a roof the component analysis values at $80,000 of original basis, with roughly $11,600 of depreciation taken so far. Tear it off in a renovation and the election deducts the remaining $68,400 this year while the new roof starts its own schedule. Skip the election and that $68,400 depreciates over the next 23-plus years inside an asset that no longer exists, then shows up again at sale as part of the recapture base.
The deadline is unforgiving
The election is made simply by reporting the loss on your timely filed return for the year the component was retired. There is no separate form, and there is no second chance: miss the year and the loss is gone. A late partial asset disposition generally cannot be made through Form 3115, because it is an election rather than an accounting method; the limited late-election window the IRS opened under the tangible property regulations closed in 2014. This is the opposite of the cost segregation look-back, where Form 3115 and a section 481(a) catch-up adjustment can reach back across closed years.
Valuing the retired component
Reg 1.168(i)-8(f) allows any reasonable method, including discounting the replacement cost back to the acquisition date using the Producer Price Index. Component-level detail from a cost segregation study makes the computation nearly mechanical, which is one more reason to document renovations as they happen rather than reconstruct them later.
When to elect
Elect when the retired component's remaining basis is meaningful, which usually means a recently purchased building or a major system. Taking a loss deduction today beats a reduction of 25 percent gain years from now in almost every bracket. Amadae's property tracking tab records renovations as they happen and computes the retired-component basis, and the loss is claimed on the return Amadae prepares. Nothing about the election requires an engineering study, just component records and the right year.