Both energy provisions have now sunset for new work. Qualifying projects that started or closed before the cut-off can still be claimed — often on an amended return.
Two long-standing energy provisions reached their statutory end this summer. If you own, develop, design or build, the practical question is no longer should we plan around these — it is did we ever claim what we already earned.
The dates
Under the One Big Beautiful Bill Act (Public Law 119-21, enacted July 4, 2025):
- §179D, the energy efficient commercial buildings deduction, terminates for property whose construction begins after June 30, 2026.
- §45L, the energy efficient home credit, terminates for homes acquired after June 30, 2026.
Both of those dates are now behind us. Nothing about that is ambiguous, and we would rather say so plainly than sell you a planning conversation about a provision that no longer applies to new work.
What remains claimable
The termination applies prospectively. It does not reach back and disqualify work that already met the tests:
- Commercial and public buildings whose construction began on or before June 30, 2026 may still support a §179D deduction, subject to the usual efficiency modeling and certification requirements.
- Homes acquired — sold or leased — on or before June 30, 2026 may still support §45L credits for the eligible contractor.
- Amended returns and prior-year claims remain available for qualifying past projects within the ordinary statute of limitations.
Who tends to have money sitting here
In our experience the buildings most likely to hold an unclaimed 179D deduction belong to owners who never heard of it, and the designers most likely to hold an allocation are the engineering and architecture firms who did the efficiency work on public projects and never asked the owner for the allocation letter.
For 45L, it is residential developers and builders who completed and sold units in the last few years and treated the credit as too small to chase. Across a subdivision it is rarely small.
How a look-back actually works
It is document work, not sales work. We establish which projects fall inside the eligible window, obtain or reconstruct the certification and modeling required, confirm the allocation chain where a government-owned building is involved, and then coordinate with your CPA on the amended return. Where the substantiation cannot be built, we say so and stop — an unsupported energy deduction is not worth the examination risk.
A closing note on timing
Statutes of limitation do not pause because a provision sunset. Every month that passes closes another tax year to amendment. If you think you have an eligible project, the window on claiming it is narrower than the window on qualifying for it ever was.