Section 179D Deduction 2026: Energy-Efficient Commercial Building Tax Guide After the June 30 Cutoff

Is 179D still worth chasing after the June 30 cutoff?

Short answer: yes, but only for projects that already started. OBBBA Section 70507 terminates the Section 179D deduction for property whose construction begins after June 30, 2026. As I write this in October 2026, that door is closed for anything new. What remains is a recovery job: buildings that broke ground on or before June 30 and have not yet been placed in service, and finished buildings where nobody filed the claim.

My read is that most owners are underestimating how much money this is. A 100,000-square-foot office building that models at 40% energy savings and meets the prevailing wage rules produces a deduction in the neighborhood of $400,000 before inflation indexing. I have seen deductions of that size die because the contractor’s payroll files were incomplete. A few hours of paperwork discipline, early, is worth more than any negotiation on the construction contract.

Section 179D is a deduction, not a credit: it reduces taxable income, not tax owed. It is calculated per square foot, not as a percentage of cost, which makes it unusual. You can spend more or less on the retrofit and the deduction does not move; only floor area and percent savings do.

This guide is for U.S. building owners, real estate investors, and the architects, engineers and contractors who design for public clients. The statute and the IRS guidance keep moving, so use the numbers below to size the opportunity and let your CPA confirm the details before anything goes on a return.

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Who can claim the 179D deduction?

The base rule is simple: the person who paid for the energy-saving work claims the deduction. That covers owners of commercial buildings and, often overlooked, multifamily residential buildings of four stories or more. If a tenant paid to replace the lighting or HVAC in a leased space, the tenant can be the claimant.

The interesting twist is for owners who owe no tax. A county courthouse, public school, state university or charity cannot use a deduction. So the statute lets the owner hand the deduction to the designer through a signed allocation. Eligible designers are the people primarily responsible for the energy design: architects, engineers, contractors, environmental consultants and energy services providers. Tax-exempt organizations and tribal governments can allocate too, a change that came in with the Inflation Reduction Act.

Owner type	Who claims	Key paperwork
Private owner (corporation, LLC, individual)	The owner	Independent certification, energy model report
Tenant who paid for improvements	The tenant	Lease/improvement records, certification
Government, school or public agency	The designer, by allocation	Allocation letter, certification
Nonprofit or tribal entity	The designer, by allocation	Allocation letter, certification

For design firms, this is a real line of business. A mid-size engineering practice working on public schools can recover a meaningful amount of tax each year just by asking for allocation letters at the start of every engagement. If your contracts do not say the owner will cooperate on allocation, fix that language now.

One practical note. If you hold the building through a pass-through entity, the deduction flows to the partners or shareholders, and the interaction with other deductions matters. I walked through a related problem in our QBI deduction guide for pass-through owners, because a large 179D deduction can lower the income that the QBI calculation starts from.

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What is the deduction actually worth per square foot?

The formula starts with floor area and percent energy savings against a reference building built to ASHRAE 90.1. The statutory figures, before inflation adjustment, look like this:

Energy savings	Base rate (per sq ft)	With prevailing wage and apprenticeship (per sq ft)
25%	$0.50	$2.50
30%	$0.60	$3.00
40%	$0.80	$4.00
50% or more	$1.00 (cap)	$5.00 (cap)

The jump in the right-hand column is the whole game. Meeting the prevailing wage and apprenticeship (PWA) requirements multiplies the rate by about five. The requirements: pay laborers and mechanics at least the locally determined prevailing wage while the work is done, and make sure a required share of total labor hours is performed by qualified apprentices. Projects that began construction before an early-2023 date were treated as satisfying PWA automatically, but whether that exception covers your project is something to verify.

Here is what it looks like on a 100,000-square-foot building certified at 40% savings:

Scenario	Deduction (pre-indexing)	Rough tax savings at 21%
Base rate only	about $80,000	about $16,800
PWA satisfied	about $400,000	about $84,000

That is a $67,000 swing, and it turns on whether somebody collected certified payroll. If I were the owner, I would require PWA compliance in the construction contract before breaking ground, with the right to withhold payment for missing records.

Two caveats. First, the rates are indexed for inflation every year, so your actual numbers will be somewhat higher than the table. Second, a deduction is only valuable if you have income to absorb it. Owners who expect to be in a loss position should talk through carryforwards. And if you are an individual owner, a big deduction changes your withholding or estimated-payment picture; our withholding tax refund guide explains how to adjust so you are not lending the IRS money all year.

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What did OBBBA Section 70507 change, and who is still in the window?

Before 2026, 179D was permanent law. The Inflation Reduction Act in 2022 made it much richer starting with buildings placed in service in 2023, which is when claim volume exploded. OBBBA then cut it off, using a construction-start test: no deduction for property whose construction begins after June 30, 2026.

The cutoff is about when work starts, not when the building is finished. That distinction creates three groups of owners today.

Situation	Outlook	What to do
Construction began on or before June 30, 2026, still being built	Likely eligible when placed in service	Lock down start-date evidence and PWA records
Began before the cutoff, finished earlier, never claimed	Possibly recoverable by amended return	Confirm the statute of limitations and whether certification can still be done
Construction begins after June 30, 2026	No 179D	Look at depreciation and other deductions instead

The hard part is proving the start date. A signed contract, a building permit and physical work on site are different pieces of evidence, and the weight each one carries depends on the facts and the guidance that applies. Two owners with the same calendar date can end up in different places if one has site photos and invoices for delivered materials and the other has only a permit. My advice: put every construction-start document, from the contract to the first grading invoice, into a single folder today while the people who remember are still around.

I expect the market to split. Owners who rushed to start work before the deadline on thin paperwork will have the weakest claims when the IRS asks questions. Owners who documented carefully will keep claiming on placed-in-service buildings for a few years yet.

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Which building systems and projects qualify?

179D looks at the building as a whole. Three systems define the scope:

• Interior lighting: LED conversions, occupancy sensors, daylight controls
• HVAC and hot water: high-efficiency chillers, heat recovery ventilation, variable air volume systems
• Building envelope: insulation, high-performance glazing, roof upgrades

A lighting retrofit by itself rarely gets to 25%. The savings figure comes from a whole-building simulation compared against the reference standard, so most successful claims combine at least two systems. Under older rules you could claim partial deductions for a single system. That is gone; the 25% whole-building threshold is the entry ticket now.

Energy-hungry buildings are natural candidates because savings scale quickly with big loads. Data centers are an obvious example, since better cooling efficiency can shift the percentage dramatically. If you are following that theme from the investment side, our AI stocks investment guide covers the infrastructure demand behind it.

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How do you actually claim it? Certification, modeling and Form 7205

The workflow I recommend:

1. Model early. Bring an energy modeler in during design, not after the building opens. You lose the chance to tune the design toward a higher savings tier.
2. Write PWA into the contract. Prevailing wage payments, apprentice ratios and payroll reporting should be contract obligations.
3. Place the building in service. That determines the tax year of the deduction.
4. Get independent certification. A qualified third party runs whole-building modeling in DOE-approved software and signs the certification.
5. File Form 7205 with your return, as owner or as allocated designer.
6. Keep the file. Certification, model output, start-date evidence and payroll records stay with your tax records.

Step	Who handles it	Watch out for
Modeling and certification	Independent engineer	No financial or family ties to owner or builder
PWA records	Contractor and owner	Certified payroll, apprentice hours
Allocation letter	Public or exempt owner	Designer named, dollar amount stated, signed
Return filing	CPA	Form 7205 attached, basis reduction recorded

Certification fees vary widely with building size and complexity. They are usually small next to the deduction, but I have seen owners pick a certifier on price alone and end up with a file that would not survive an exam. Pick one who has defended certifications before.

If you are the designer or contractor on these jobs, remember that your own risk profile matters too. Large deductions backed by certifications and payroll files are a place where management signs and management answers, so it is worth reviewing your directors and officers liability insurance at the same time.

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What happens after you take the deduction?

Three follow-on effects catch people off guard.

First, the deduction reduces the building’s tax basis by the amount deducted. That raises taxable gain on a future sale. For a building you plan to hold for decades, that is a minor cost against a large near-term deduction. For a flip, run the math.

Second, there is a three-year look-back. The same building can get another 179D deduction only after the three-year gap and only with new qualifying improvements. A long-term owner can plan retrofit phases around that rhythm.

Third, for an allocated designer, the treatment is different: the designer is not the owner, so there is no basis reduction, and the deduction simply reduces income. That asymmetry is why public-sector architecture and engineering firms treat 179D as a recurring revenue-like benefit.

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What mistakes do people make most often?

These are the ones I see repeated.

Mistake	Consequence	Fix
Thin proof of construction start	Cannot show eligibility under the cutoff	Contracts, permits and site records in one file
Certifier not independent	Certification may be invalid	Get written confirmation of no related-party tie
Missing PWA payroll records	Rate drops to one-fifth	Make records a contract obligation
Wrong reference standard	Savings overstated	Confirm the standard for the placed-in-service year
No signed allocation letter	Designer’s deduction denied	Get the letter before the return is filed
Basis reduction ignored	Understated gain on sale	Have the CPA track it
Equipment changes after certification	Model no longer matches the building	Remodel after changes

The most expensive error by far is the PWA paperwork gap. A building can follow every wage rule in reality and still be paid at the base rate because nobody can prove it. The second most expensive is a certifier who works for the contractor. It looks cheaper and then falls apart in an exam, and when a certification fails, the whole deduction goes with it.

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What should owners do this quarter?

The sequence is short. First, list every project that began construction on or before June 30, 2026. Second, audit the start-date evidence and the PWA records for each. Third, if any finished building never claimed 179D, ask your CPA whether an amended return is still open. Fourth, if the building is public or tax-exempt, open the allocation letter conversation with the owner now.

If you also manage a securities portfolio, think about how a large real-estate deduction fits with gains elsewhere; our stock capital gains tax guide covers the investment side of that planning.

My closing view: with new starts over, 179D has shifted from an incentive you plan around to an asset you collect. Paper trails fade with time, so collecting sooner is cheaper than collecting later.

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This article is for general information only and is not tax or legal advice. Deduction rates, inflation-adjusted amounts, construction-start rules and filing deadlines can change under statute and IRS guidance. Confirm current figures and your specific facts with a CPA or tax attorney and the IRS before filing.