Casualty events and depreciation: storms, fires, and the value of component detail

A serious casualty — hurricane, fire, flood — triggers four overlapping computations, and every one of them runs on basis detail. First, the casualty loss (or, with good insurance, the casualty gain) under Section 165. Second, the retirement of destroyed components, where a partial disposition election under Treas. Reg. §1.168(i)-8(d) deducts the remaining basis of the roof, systems, and interiors that no longer exist. Third, Section 1033, which defers insurance-funded gain if proceeds are reinvested in replacement property in time. Fourth, the repair regulations, which force capitalization of the restoration to the extent a loss or insurance basis adjustment was taken — Treas. Reg. §1.263(a)-3(k)(1)(iii). An owner whose fixed-asset ledger shows one line — "Building, $6,000,000" — has to reconstruct component basis under audit pressure. An owner with a cost segregation study already has the numbers.

The four computations, in order

1. Measure the casualty result. For business property fully destroyed, the loss is adjusted basis less insurance; for partial destruction, the lesser of basis or the decline in value, less insurance. Well-insured property routinely produces gain — proceeds above the depreciated basis — which is where Section 1033 enters. Federally declared disasters bring elective timing rules (Section 165(i) allows deducting in the prior year) and longer replacement windows.

2. Retire what was destroyed. Continuing to depreciate a roof that blew off is both wrong and wasteful. The partial disposition election under Treas. Reg. §1.168(i)-8 recognizes the remaining basis of each destroyed component as a retirement loss — but note the interaction: basis recovered as a casualty loss or offset by insurance cannot be deducted twice. In practice the disposition and casualty computations share one basis pool, and the ordering workpaper is the whole ballgame. For destroyed components the disposition rules are mandatory in the casualty context, not merely elective, once a loss is claimed with respect to them.

3. Defer the gain under Section 1033. An involuntary conversion's gain is deferred to the extent proceeds are reinvested in property "similar or related in service or use" — a stricter standard than 1031's like-kind, though Section 1033(g) relaxes it to like-kind for condemned business real estate. The window is generally two years from the close of the year gain is realized; four years in a federally declared disaster area under Section 1033(h), which also treats any tangible business replacement property as similar-in-use. The replacement property's basis is reduced by deferred gain — the deferral is a loan against future depreciation, and eventual recapture.

4. Capitalize the restoration. No repair deduction for rebuilding what the casualty destroyed, up to the basis adjustment taken: §1.263(a)-3(k)(1)(iii) makes restoration-after-casualty a per se improvement. Spending beyond that ceiling can still be tested under the ordinary repair standards. The capitalized rebuild is new property — new recovery periods, frequently 100 percent bonus on qualifying components acquired after January 19, 2025, and a fresh chance to classify correctly from day one.

Why component detail pays exactly here

One $6M building, roof and HVAC destroyed, $900K insurance (illustrative).

Every row is an exam issue when estimated and a footnote when documented. The reasonable-methods backstop in §1.168(i)-8(f) (producer-price-index discounting, allocations) exists precisely because most owners lack the detail — but examiners test estimates hard, and the Cost Segregation Audit Techniques Guide is their playbook for both directions of the file. The disposition loss and any Section 1033 statements ride on the return with the depreciation reboot on Form 4562; replacement-period elections and extensions are worth calendaring the week the adjuster shows up, not at filing. If the property never had a study, the casualty year is a defensible moment to commission one — the engineering visit that prices the rebuild can document the component basis at the same time.