The Section 179D Energy Efficient Commercial Buildings Deduction has officially reached a significant legislative cutoff.
Under the One Big Beautiful Bill Act, Section 179D was amended to terminate for property for which construction begins after June 30, 2026.
That has created an understandable misconception: 179D is over.
For some future projects, that will eventually be true. But for many projects already underway, the opportunity may still exist.
The key is understanding what the June 30, 2026 deadline actually means and which projects should still be evaluated.
Misconception #1: 179D Ended on June 30, 2026
Not exactly.
The legislation did not simply eliminate Section 179D for all property after June 30, 2026. Instead, it established a cutoff based on when construction begins.
Section 179D does not apply to property for which construction begins after June 30, 2026.
That distinction is important.
Projects involving qualifying property for which construction began on or before June 30, 2026, may continue to qualify, provided all other Section 179D requirements are satisfied.
In other words, the property does not necessarily need to be completed or placed in service by June 30, 2026.
For building owners, designers, and tax professionals, the question should therefore not simply be:
“Is 179D still available?”
A better question is:
“When did construction begin on this project?”
Misconception #2: Only Projects Completed Before the Deadline Can Qualify
This is one of the most important distinctions building owners and developers need to understand.
The June 30, 2026 cutoff relates to the beginning of construction, not completion or placed-in-service date.
Consequently, qualifying projects that started construction before the deadline may still warrant a 179D evaluation, even if substantial construction activities continue beyond June 30.
This may include:
- New commercial building construction.
- Major building renovations.
- HVAC system replacements and upgrades.
- Interior lighting improvements.
- Building-envelope improvements.
- Qualifying energy-efficient building retrofit projects.
As more time passes from the June 30 deadline, documentation will become increasingly important. Project teams should retain contracts, construction schedules, invoices, work records, and other materials that may help establish the project's timeline.
Misconception #3: 179D Is Only Available to Building Owners
Building owners remain an important beneficiary for 179D, but they are not the only parties who may benefit.
Under the current rules, eligible designers may claim the deduction for qualifying energy-efficient commercial building property or retrofit property installed in buildings owned by specified tax-exempt entities.
These entities can include:
- Federal, state, and local government entities.
- Certain tax-exempt organizations.
- Indian tribal governments.
- Alaska Native Corporations.
Depending on the project, eligible designers could include an architect, engineer, contractor, environmental consultant, or energy services provider primarily responsible for designing the qualifying property.
This means architecture, engineering, and other design firms should not automatically stop evaluating 179D opportunities simply because the provision has been terminated for future construction. There may still be a meaningful pipeline of projects that began construction on or before June 30, 2026.
Misconception #4: There Is No Reason to Review Older Projects
Another common misconception is that 179D only matters for projects happening right now.
The sunset makes historical project reviews particularly important.
Many businesses and their CPAs may have completed qualifying construction or renovation projects without ever evaluating the potential Section 179D deduction. Designers may also have worked on eligible projects without pursuing an available designer allocation.
Rather than focusing exclusively on new construction, this is an important time to review project history.
Questions to consider include:
- Were commercial buildings constructed or significantly improved in recent years?
- Were lighting, HVAC, service water heating, or building-envelope systems upgraded?
- Did an architecture or engineering firm design qualifying energy-efficient systems for a government-owned or tax-exempt building?
- Were projects previously evaluated but never completed through the 179D certification and tax filing process?
- Are there projects currently under construction that began on or before June 30, 2026?
A portfolio-level review can help identify opportunities across multiple properties, projects, and tax years that may otherwise be overlooked.
Misconception #5: Every Eligible Project Receives the Same Deduction
Establishing eligibility is only the first step.
The amount of the 179D deduction can depend on factors including the building's energy-efficiency performance, square footage, applicable requirements, and whether prevailing wage and apprenticeship requirements are satisfied.
For projects subject to those requirements, proper documentation can have a significant impact on the available deduction.
This makes early review valuable, even for projects that have already begun construction.
Who Should Still Be Looking at 179D?
Despite the June 30, 2026 cutoff, 179D should remain on the radar for:
- Commercial building owners with qualifying projects that began construction on or before June 30, 2026.
- Architects, engineers, and other eligible designers that worked on qualifying buildings owned by tax-exempt entities.
- Developers and real estate owners with projects currently under construction that crossed the June 30 deadline after work had already begun.
- CPAs and tax advisors with clients that constructed, renovated, or improved commercial buildings in prior years and may not have evaluated 179D.
The opportunity is becoming more finite, but that makes identifying the remaining eligible projects more important, not less.
The Takeaway: 179D Has a Construction Cutoff, Not an Immediate Off Switch
The sunset of Section 179D changes the future of the deduction, but it does not mean every 179D opportunity disappeared after June 30, 2026.
Projects for which construction began on or before the deadline may still qualify, and prior projects may still deserve another look.
For building owners, designers, and their CPAs, now is the time to understand which projects remain in the 179D pipeline, document when construction began and evaluate potential benefits before opportunities are overlooked.
The window for new Section 179D opportunities has closed for property beginning construction after June 30, 2026. However, the opportunity to identify and capture remaining eligible deductions has not necessarily disappeared.
Source Advisors can help review individual projects or a broader property portfolio to determine which properties may still qualify for the Section 179D deduction and what documentation is needed to support the deduction.
