Section 179 vs Bonus Depreciation for a Roof or HVAC

For a nonresidential building, §179 can reach a new roof or building-wide HVAC improvement that bonus depreciation under §168(k) cannot if the improvement is qualified real property under §179(e) placed in service after the building was first placed in service and the taxpayer’s §179(b) limits allow the deduction, and a cost segregation study can still identify separate 5-, 7-, and 15-year assets that may qualify for bonus depreciation on the 2026 return.

The practical answer is not “§179 or bonus” in isolation: use cost segregation to separate the project into its proper recovery classes, then have your tax advisor apply §179(e), §179(b), §179(d)(5), and §168(k) to the parts that each rule can actually reach.

Can I use §179 instead of bonus depreciation for a roof, HVAC, fire protection, or security system on a commercial building?

Yes, if the improvement is qualified real property under §179(e) and the taxpayer satisfies the §179 limits, §179 can apply to certain nonresidential building improvements that bonus depreciation under §168(k) cannot reach. Section 179(e) adds qualified real property to §179 property, and qualified real property includes qualified improvement property plus roofs, heating, ventilation and air-conditioning property, fire protection and alarm systems, and security systems that are improvements to nonresidential real property placed in service after the date the building was first placed in service.

Bonus depreciation under §168(k) applies only to qualified property with a recovery period of 20 years or less, including the 5-year, 7-year, and 15-year property a cost segregation study identifies and qualified improvement property when it meets the 15-year qualified improvement property rules. Bonus depreciation under §168(k) does not apply to land, the 39-year nonresidential building shell, a new roof treated as a 39-year structural component, or a building-wide HVAC system treated as a 39-year structural component.

That is why cost segregation matters even when the owner is focused on §179: the study helps separate the roof or HVAC project from shorter-life electrical, plumbing, specialty equipment, site, or interior components that may have a different answer under §168(k), §168(d), and §179. For more on qualified improvement property as a 15-year asset, see qualified improvement property and the 15-year asset rules.

Planning rule: §179 may be the only accelerated route for a commercial roof or building-wide HVAC system that is qualified real property under §179(e), when the taxpayer’s §179(b) limits allow the deduction, while cost segregation may identify other project costs that qualify for §168(k) bonus depreciation.
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What does placed in service mean for my 2026 commercial improvement?

Property is placed in service when it is in a condition or state of readiness and availability for its specifically assigned function under Treas. Reg. §1.46-3(d)(1)(ii) and Treas. Reg. §1.167(a)-11(e)(1)(i), and for a calendar-year taxpayer, an improvement placed in service by December 31, 2026 can be depreciated on the 2026 return.

For a roof, the placed-in-service date is generally when the roof is ready and available to protect the building for its intended business or rental use under Treas. Reg. §1.46-3(d)(1)(ii), not merely when the proposal was signed or when invoices were received. When the replaced roof was a depreciable asset of the taxpayer, a partial disposition election under Treas. Reg. §1.168(i)-8(d), generally made on the timely filed original return (including extensions) for the year the old roof is disposed of, can let the owner recognize a loss for the old roof’s remaining adjusted basis instead of continuing to depreciate it; see When You Renovate, Stop Depreciating the Wall You Tore Out. For HVAC, fire protection, alarm, or security improvements, the placed-in-service date is generally when the system is installed, tested as appropriate for its function, and ready and available for use in the nonresidential building under Treas. Reg. §1.167(a)-11(e)(1)(i).

For a calendar-year taxpayer, a commercial improvement placed in service on January 1, 2027 or later is first depreciated on the 2027 return, while a fiscal-year taxpayer uses the end of its own tax year under the general depreciation timing rules of §168. A cost segregation study for the 2026 return should therefore focus on the assets that are actually ready and available for their intended use during the 2026 tax year.

What changes on the 2026 return if cost segregation breaks out the project?

Cost segregation changes the 2026 return by moving properly identified components out of the 39-year nonresidential real property bucket and into shorter MACRS classes when the facts support that treatment under §168. A study built on the methodology in the IRS Cost Segregation Audit Techniques Guide reviews project costs, drawings or invoices when available, and property use to estimate what belongs in 5-year, 7-year, 15-year, 39-year, and land categories.

For a commercial roof or HVAC project, the roof membrane, roof structure, or central building HVAC may remain 39-year §1250 property, but certain dedicated process systems, specialty electrical, removable finishes, site improvements, or qualified improvement property may be separately classified when the facts support that treatment under §168 and related guidance. Cost segregation does not turn every building component into bonus-eligible property; it documents which assets are not part of the 39-year building shell.

Under §168(k), bonus depreciation is 100% for qualified property acquired after January 19, 2025, when the acquired date is determined under IRS Notice 2026-11 and Treas. Reg. §1.168(k)-2(b)(5)(ii)(B), not merely by the closing date. Under IRS Notice 2026-11, for a written binding contract, the acquired date is the latest of the date the contract was signed, the date it became enforceable under state law, the end of any cancellation period, and the date any contingency was satisfied, and the written binding contract must be enforceable under state law without limiting damages to a specified amount through a liquidated damages clause or similar provision.

Under Treas. Reg. §1.168(k)-2(b)(5)(iii) and Treas. Reg. §1.168(k)-2(b)(5)(v), if the contract is not binding in that sense, the acquired date is generally when the taxpayer has paid or incurred more than 10 percent of the total cost, excluding land and preliminary activities. For self-constructed property, including property built for the taxpayer under a written binding contract entered into before construction began, Treas. Reg. §1.168(k)-2(b)(5)(iv) treats the property as acquired when physical work of a significant nature begins, and paying or incurring more than 10 percent of the total cost, excluding land and preliminary activities, is a safe harbor under Treas. Reg. §1.168(k)-2(b)(5)(iv)(B)(2).

Qualified property acquired on or before January 19, 2025 and placed in service in 2026 stays on the TCJA phase-down at 20% for 2026 under §168(k), except long-production-period property and certain aircraft under §168(k)(2)(B) and §168(k)(2)(C), which run a year behind. Used property qualifies for bonus depreciation only when the used-property rules of §168(k)(2)(E)(ii) are satisfied, and a taxpayer may elect out of bonus depreciation for a class of property for a taxable year under §168(k)(7).

When is §179 better than bonus depreciation for these commercial improvements?

§179 is better than bonus depreciation when the improvement is qualified real property under §179(e), bonus depreciation under §168(k) is unavailable because the asset is 39-year property, and the taxpayer can use the §179 deduction under the limits in §179(b). Section 179 is elected, is capped by the dollar limitation in §179(b)(1), is reduced by the investment phase-out in §179(b)(2), and cannot exceed the taxpayer’s taxable income from the active conduct of any trade or business under §179(b)(3), with the excess carried forward under §179(b)(3)(B).

A noncorporate lessor has an additional gate because §179(d)(5) applies extra requirements to property leased to others by a noncorporate lessor. Improvements to residential rental buildings are not qualified real property under §179(e), so the §179 roof, HVAC, fire protection, alarm, and security system rule discussed here is for nonresidential real property.

For a building owner using the property in an active operating business, §179 may create a current deduction if §179(b)(3) taxable income from the active conduct of any trade or business is sufficient. For a landlord, the §179 answer depends on the leasing structure, entity type, noncorporate lessor rules under §179(d)(5), passive-activity limits under §469, and other owner-level limits, so the tax advisor typically runs the §179 limits rather than treating the roof invoice as automatically deductible.

How do the §168(d) conventions affect a late-2026 commercial project?

The §168(d) conventions affect regular depreciation timing, but bonus depreciation under §168(k) is not reduced by a convention when bonus is claimed. Nonresidential real property with a 39-year recovery period uses the mid-month convention under §168(d), so a 39-year commercial roof or HVAC structural component placed in service in any part of a month is treated as placed in service at the middle of that month and receives half a month of regular depreciation for that month.

Other MACRS property, including 5-year, 7-year, and 15-year property identified by cost segregation, generally uses the half-year convention under §168(d) unless the mid-quarter convention applies under §168(d)(3). The mid-quarter convention applies under §168(d)(3)(A) when the aggregate basis of property placed in service during the last three months of the taxable year is more than 40% of the aggregate basis of all property placed in service during that taxable year, excluding residential rental and nonresidential real property under §168(d)(3)(B).

Under the mid-quarter convention in §168(d), fourth-quarter property receives one and a half months of first-year regular depreciation, so the convention matters mainly for property on which bonus depreciation is not claimed. Basis expensed under §179 is left out of the 40% test (Treas. Reg. §1.168(d)-1(b)(4)); have the tax advisor confirm how bonus-depreciated basis is counted and run the test on the full placed-in-service schedule.

When does cost segregation not help with a roof or HVAC project?

Cost segregation does not help when the project is only 39-year structural property, the §179 limits do not allow a usable deduction, and the owner cannot use the accelerated deductions under the passive-activity and owner-level limitation rules. A cost segregation study is worth it when three conditions hold together: the basis is large enough for the accelerated deductions to outweigh the cost of the study, the deduction is usable this year given the owner's passive-activity position, and the hold is long enough to survive recapture. All three, or the honest answer is no.

A rental activity is passive under §469(c)(2) unless an exception such as §469(c)(7) applies, and a passive loss that passive income does not absorb is disallowed under §469(a) and carried forward under §469(b). Under §469(i), an individual who actively participates in a rental real estate activity (a separate test from material participation, and one that requires an interest of at least 10% by value (a spouse’s interest counts) throughout the year) is exempt from the §469(a) disallowance for up to $25,000 of loss from the rental real estate activities in which the individual actively participates; the $25,000 is reduced by 50% of modified adjusted gross income above $100,000 and is gone at $150,000, and for a married individual filing separately it is $12,500, phasing out between $50,000 and $75,000, only if the spouses lived apart for the entire year, and zero if they lived together at any time during the year.

Under §469(c)(7), a taxpayer is a real estate professional only if more than one-half of the personal services the taxpayer performs in trades or businesses during the year are performed in real property trades or businesses in which the taxpayer materially participates, and the taxpayer performs more than 750 hours of services during the year in real property trades or businesses in which the taxpayer materially participates (on a joint return, one spouse must meet both tests alone); the rental loss is then nonpassive only if the taxpayer also materially participates in that rental activity, with each rental tested separately unless the election under Treas. Reg. §1.469-9(g) to treat all interests in rental real estate as one activity was made. If a loss is nonpassive, it can offset wages or other nonpassive income only when the basis rules, at-risk rules under §465, and excess business loss rules under §461(l) also allow the deduction.

On a taxable sale at a gain, recapture applies up to the amount of that gain, however long the property was held, outside the Opportunity Zone rule that, for a qualifying investment held at least 10 years with the IRC §1400Z-2(c) election, applies on a sale of the qualified opportunity fund interest. Section 1245 recapture on 5-year and 7-year property is ordinary income, §1250 recapture of depreciation taken above straight-line, including bonus, on 15-year land improvements held more than one year is ordinary income, and the rest of the depreciation on those land improvements and on the 39-year structure is unrecaptured §1250 gain taxed at up to 25% for a noncorporate taxpayer.

If the property is in an Opportunity Zone structure, coordinate the cost segregation and exit modeling with the IRC §1400Z-2 rules and review Opportunity Zone cost segregation planning. An owner who wants a screening step before engaging a study can start with the ClickDrag cost segregation qualifier.

What documents should I gather before deciding on a study?

A cost segregation review classifies the project accurately when it starts from the documents that show what was acquired, built, replaced, and placed in service. For a roof, HVAC, fire protection, alarm, or security project, the useful documents are the closing or settlement statement if the building was acquired, construction costs and invoices, contractor pay applications, the current depreciation schedule, and a land-value source such as an assessor ratio or appraisal.

An owner comparing providers can look for a process built on the methodology in the IRS Cost Segregation Audit Techniques Guide and supported by engineering-based cost review rather than a flat percentage allocation. Practical selection criteria are compared at best cost segregation companies, and the qualifier helps decide whether a 2026 commercial improvement is worth reviewing before the return is prepared.

What if the commercial improvement was placed in service in an earlier tax year?

If the building improvement was placed in service in 2026, the depreciation classification belongs on the original 2026 return and no Form 3115 is needed for that current-year placement. If you placed the building or improvement in service in 2024 or earlier and still own it at the start of the 2026 year of change, Form 3115 filed with the 2026 return can report missed depreciation as a §481(a) adjustment, with no amended returns, when the property has been depreciated on two or more filed returns and the eligibility rules in section 6.01 of Rev. Proc. 2025-23 are satisfied under the procedures of Rev. Proc. 2015-13.

For a building you placed in service in 2025 with the 2025 return filed, Form 3115 with the 2026 return or an amended 2025 return filed before the 2026 return is filed are both available when the taxpayer still owned the property at the start of the 2026 year of change and the other eligibility rules in section 6.01 of Rev. Proc. 2025-23 and Rev. Proc. 2015-13 are satisfied. A prior election out of bonus depreciation cannot be undone through this automatic accounting method change under section 6.01(1)(c)(vi) of Rev. Proc. 2025-23, so confirm the route with your tax advisor.

Frequently Asked Questions

Can bonus depreciation apply to a new roof on a commercial building?

No, bonus depreciation under §168(k) does not apply to a new roof when the roof is a 39-year structural component of nonresidential real property. Bonus depreciation applies only to qualified property with a recovery period of 20 years or less, while §179(e) may apply to a qualifying roof improvement to nonresidential real property if the §179(b) and §179(d)(5) limits are satisfied.

Can §179 apply to HVAC on a nonresidential building?

Yes, §179 can apply to heating, ventilation, and air-conditioning property when it is qualified real property under §179(e), the improvement is to nonresidential real property, and the §179(b) limits allow the deduction. The taxable income limit in §179(b)(3), the investment phase-out in §179(b)(2), and the noncorporate lessor rules in §179(d)(5) can change the result.

Where does cost segregation fit if §179 already covers the roof or HVAC?

Cost segregation fits because the same project may include assets that are not the roof or building-wide HVAC system and may qualify for shorter recovery periods under §168. A cost segregation study can identify 5-year, 7-year, and 15-year property that may be eligible for §168(k) bonus depreciation, while the tax advisor separately applies §179 to qualified real property.

Does qualified improvement property get bonus depreciation in 2026?

Yes, qualified improvement property can get bonus depreciation in 2026 when it is 15-year property, is qualified property under §168(k), and satisfies the acquisition and placed-in-service rules. Under IRS Notice 2026-11 and Treas. Reg. §1.168(k)-2(b)(5)(ii)(B), the acquired date for a written binding contract depends on enforceability, cancellation periods, and contingencies, not merely the date the contract was signed.

Do I need Form 3115 for a 2026 roof, HVAC, fire protection, or security project?

No, you do not need Form 3115 for a 2026 project when the improvement is first placed in service in 2026 and the classification is reported on the original 2026 return. Form 3115 under section 6.01 of Rev. Proc. 2025-23 and Rev. Proc. 2015-13 is a catch-up route for eligible property placed in service in an earlier tax year, including property you placed in service in 2024 or earlier and still own at the start of the year of change.

Section 179 vs Bonus Depreciation for a Roof or HVAC: Where Cost Segregation Fits