Who Qualifies for the 179D Deduction Now That the Sunset Has Passed?

TL;DR: More people than you would guess, for years to come. Congress ended new 179D eligibility for projects that begin construction after June 30, 2026, and that date is behind us. But the deduction did not vanish on July 1. Buildings that started construction on or before the deadline still qualify when they are placed in service, even if that happens in 2027 or 2028. Building owners can still capture the deduction for energy-efficient property already in service. And architects, engineers, and design-build contractors can still claim allocated deductions on government and tax-exempt projects, including ones finished years ago. The door is closing slowly, not slammed.

Key Takeaways

• The One Big Beautiful Bill Act terminated 179D for property whose construction begins after June 30, 2026. The controlling date is when construction began, not when the building is finished, so qualifying projects will keep coming into service for the next several years.
• The deduction is worth up to $5.94 per square foot in 2026 for projects meeting prevailing wage and apprenticeship requirements, on a sliding scale tied to modeled energy savings. Without those requirements the range runs roughly $0.59 to $1.19 per square foot. On a 100,000 square foot building, that spread is the difference between about $59,000 and $594,000.
• Three groups still qualify: owners of commercial buildings with eligible property, owners of residential buildings four stories or taller, and the designers of buildings owned by governments and tax-exempt entities, who receive the deduction through an allocation letter.
• Designers have the longest runway. A firm that designed a qualifying school, courthouse, or nonprofit hospital placed in service in a prior open tax year may still be able to claim it. Those allocation letters are worth chasing now, while records and relationships are fresh.

What exactly is 179D?

Section 179D is a deduction, not a credit, for energy-efficient commercial building property: interior lighting, HVAC and hot water systems, and the building envelope. Qualification is measured against an ASHRAE reference standard using energy modeling, and the results have to be certified by a qualified third party after a field inspection. The reward scales with performance. In 2026, a building that models at least 25% energy savings earns the base deduction, and each additional percentage point of savings raises the rate until it tops out at 50% savings.

The multiplier that matters most is labor compliance. Projects meeting prevailing wage and apprenticeship requirements earn roughly five times the base rate, which is how the 2026 numbers reach $2.97 to $5.94 per square foot instead of $0.59 to $1.19. Square footage does the rest of the work. This is a deduction that rewards big roofs: warehouses, schools, offices, hospitals, multifamily towers.

Didn't 179D just expire?

It sunset, which is different from expiring, and the difference is worth real money. The One Big Beautiful Bill Act ended eligibility for property that begins construction after June 30, 2026. Beginning of construction is the trigger, and under the IRS framework it can be met by starting physical work of a significant nature or by the five percent safe harbor on project costs.

Follow that logic forward. A developer who broke ground on a distribution center in May 2026 will place it in service in 2027, and it qualifies. A hospital wing that started construction in June 2026 might not open until 2028, and it qualifies. Projects already in the ground did not lose anything on July 1. What ended is the ability to start something new and have it count.

That creates two very different to-do lists. If you own or designed anything that began construction before the deadline, your task is documentation: nail down the construction start evidence now, because you will need it when the deduction is claimed. If you were hoping to qualify a project that has not broken ground, that opportunity is gone at the federal level, and anyone telling you otherwise is selling something.

Who can still claim it?

Building owners. If you own a commercial building, or a residential building four stories or taller, with qualifying energy-efficient property that began construction in time, you claim the deduction in the year the property is placed in service. Owners also have a lookback path: for buildings already in service in earlier years, your tax professional may be able to capture missed 179D deductions through an accounting method change rather than amended returns. The modeling, inspection, and certification still have to be done, which is where a 179D study comes in. I deliver these through my relationship with CSSI (Cost Segregation Services, Inc.).

Designers of tax-exempt buildings. Governments, schools, churches, and other tax-exempt entities cannot use a deduction, so the law lets them allocate it to the building's designer: the architect, engineer, or design-build contractor who created the technical specifications. The transfer happens through an allocation letter signed by the building owner's authorized representative. For design firms, this is found money on work already delivered. A firm that has designed a handful of municipal buildings, K-12 schools, or university facilities over the past few years may be sitting on six or seven figures of unclaimed deductions.

One nuance designers should hear plainly: your claim generally belongs on the return for the year the building was placed in service, so reaching back into prior years means amending returns that are still open under the statute of limitations. The window closes year by year. That is the real deadline pressure in 2026, more than the sunset itself.

What should you do before year-end?

Three moves, in order. First, inventory. List every project, owned or designed, that was placed in service in an open tax year or that began construction on or before June 30, 2026. Second, evidence. Pull the documentation that proves construction start dates, and for designers, identify who at the government or tax-exempt owner can sign an allocation letter. Third, model. Energy modeling and certification determine whether a project clears 25% savings and how far up the sliding scale it lands, and that analysis is exactly the thing you can get done at no cost before deciding anything.

Some projects will not clear the bar. Older systems, minimal envelope work, or savings that model below 25% mean no deduction, and it is better to hear that in a free analysis than after paying for a study. I will tell you which side of the line your project sits on.

FAQ

Is the 179D deduction still available in 2026? Yes, for property whose construction began on or before June 30, 2026. Those projects qualify when placed in service, even in later years. Property that begins construction after that date is no longer eligible under the One Big Beautiful Bill Act.

How much is the 179D deduction worth? In 2026, roughly $0.59 to $1.19 per square foot at base rates, and $2.97 to $5.94 per square foot for projects meeting prevailing wage and apprenticeship requirements, scaling with modeled energy savings between 25% and 50%.

Who counts as a designer for a 179D allocation? The person or firm that created the technical specifications for the energy-efficient property, typically architects, engineers, and design-build contractors. Installers working from someone else's specifications generally do not qualify. The building owner allocates the deduction through a signed allocation letter.

Can designers claim 179D for past projects? Often yes, for buildings placed in service in tax years still open under the statute of limitations, by amending those returns with a proper allocation letter and certification. The open window shrinks every year, which makes this worth evaluating now.

Does 179D apply to apartment buildings? Yes, if the residential building is four stories or taller. Shorter residential buildings fall outside 179D, though they may benefit from other energy incentives and from cost segregation.

The runway is shorter every quarter

179D is now a strategy with an expiration date, and the projects that qualify are a fixed pool that only drains. If you own a building placed in service in recent years, have a project that broke ground before June 30, or run a design firm with public-sector work in its portfolio, the analysis costs nothing and tells you exactly what is on the table. No obligation, no documents to assemble first, and if your projects will not clear the energy bar, I will say so and save you the fee. The service details are at davidhwiener.com.

Grab a time on Calendly at calendly.com/david-wiener/cs or call 770-224-8504, option two.

This article is educational and is not tax, legal, or accounting advice. Every situation is different; work with a qualified tax professional before acting on any strategy described here.