179D deduction window closes: what facilities and construction teams must do before June 30

The clock on Section 179D ran out faster than most facilities teams realized. The One Big Beautiful Bill Act, signed into law on July 4, 2025, inserted a termination clause into the Internal Revenue Code: 179D shall not apply to any property whose construction begins after June 30, 2026. As of today, that date has passed, making any project that broke ground on or before June 30 the final eligible cohort for one of the largest federal tax incentives available to commercial building owners and their design teams.

For enterprise operators managing large real estate portfolios or ongoing capital construction programs, the practical question is no longer whether to pursue 179D but whether active projects were properly documented and structured to qualify before the cutoff.

What the deduction is worth at scale

The U.S. Department of Energy's guidance makes the dollar value concrete. For the 2025 taxable year, a project that meets only the energy efficiency criterion qualifies for a deduction of $0.58 to $1.16 per square foot of floor area. The minimum requires demonstrating at least 25% savings against the baseline. That ceiling rises sharply when the project also satisfies prevailing wage and registered apprenticeship requirements: the deduction jumps to a range of $2.90 to $5.81 per square foot, exactly five times the base rate.

On a 100,000-square-foot property, that top-line figure translates to up to $581,000 in federal tax deductions for a single qualifying project, as DOE's own illustration shows. The deduction amount is capped at the actual cost of the energy-efficient property placed in service and is subject to a three-to-four-year look-back limit on prior deductions claimed.

Two pathways, different eligibility rules

179D offers two distinct compliance routes, and choosing the wrong one can disqualify a project entirely. The Traditional (Modeling) Pathway, formally called the deduction for energy-efficient commercial building property, applies to both new construction and building upgrade projects. It requires computer-modeled comparisons of annual energy and power cost savings between the proposed building and a reference building built to ASHRAE Standard 90.1, and the building must be located in the United States within ASHRAE's scope.

The Alternative (Measurement) Pathway, formally the deduction for energy-efficient building retrofit property, is available only for upgrades. Critically, the building must have been in service for at least five years before the qualified retrofit plan was established. This pathway uses measured site energy use intensity before and after the upgrade rather than modeled projections, which can simplify documentation for existing facilities with good metering infrastructure.

Eligible systems under both pathways include interior lighting, HVAC, service water heating, and the building envelope. Specialty process equipment and other energy loads do not qualify. The Partially Qualifying Property Pathway and the Interim Lighting Rule no longer exist under current rules, so projects that were structured around those older provisions need immediate review.

Tax-exempt entities and the allocation mechanism

Government agencies, tribal entities, and nonprofit organizations cannot claim a tax deduction directly, but they can allocate it. Under the rules updated by the Inflation Reduction Act and carried forward through the current statute, these specified tax-exempt entities may transfer their 179D deduction to the designer primarily responsible for the energy-efficient property, typically the engineer or architect of record. This allocation mechanism has made 179D directly relevant to architecture and engineering firms working on public sector projects, since they can now capture the deduction value as a fee component or competitive advantage.

For facilities teams at universities, municipalities, and healthcare systems doing energy retrofits, understanding whether your A/E contract addresses deduction allocation is now a contract administration issue, not just a tax question.

Prevailing wage and apprenticeship requirements change the math significantly

The five-to-one multiplier tied to prevailing wage and registered apprenticeship compliance is not automatic. Contractors must pay wages at rates established under the Davis-Bacon Act for the relevant locality and trade, and a specified percentage of labor hours must be performed by registered apprentices. The IRS has published detailed guidance on these requirements. For procurement teams writing construction contracts on projects started before the June 30 cutoff, those specifications need to be in the contract language now, not added retroactively.

What this means for your team

• Audit your active capital projects immediately: confirm which broke ground before July 1, 2026, and are therefore still eligible. Secure dated construction documentation for each.
• Review whether prevailing wage and apprenticeship requirements are written into existing subcontracts. Meeting those criteria is the difference between a $0.58/ft² and a $5.81/ft² deduction.
• If your organization is a tax-exempt entity (government, nonprofit, tribal), check whether your A/E contracts include 179D allocation language. A designer cannot claim an allocated deduction without an explicit election from the building owner.
• Consult a tax professional to confirm the applicable taxable year, verify which compliance pathway applies to each project, and calculate the basis reduction required under IRC Section 179D(e) when the deduction is taken.