What if your next project automatically flagged every federal, state, and utility incentive it qualified for, before you finalized the design, not after? Right now, that doesn't happen for most projects. The 179D tax deduction and the 45L tax credit represent real money for developers who qualify, and a meaningful share of eligible projects never claim either one. Not because the developers don't want the money. Because nobody on the project team was tasked with checking.
That gap matters more this year than it has in a long time, because the rules around both programs just changed in a way most development teams haven't fully absorbed yet.
Two Federal Incentives, Two Very Different Structures
179D and 45L get mentioned together constantly, which causes confusion: they're not the same program applied to different buildings. They're structurally different incentives that happen to both live in the energy-efficiency corner of the tax code.
Section 179D is a deduction for owners of commercial buildings (and, in certain cases, for the designers of record, architects, engineers, and design-build contractors, on buildings owned by government agencies and other tax-exempt entities that can't use the deduction themselves). It's calculated on a per-square-foot basis, tied to how far the building's modeled energy performance exceeds a reference standard set by ASHRAE 90.1. The better the performance above baseline, the larger the deduction per square foot, with additional value available for projects that meet prevailing wage and apprenticeship requirements. It was first introduced under the Energy Policy Act of 2005, made a permanent part of the tax code in 2020, and substantially expanded by the Inflation Reduction Act in 2022, which lowered the qualification bar and restructured the sliding scale.
Section 45L, by contrast, is a credit rather than a deduction, calculated per dwelling unit rather than per square foot, and aimed at builders and developers of new (or substantially reconstructed) residential units, single-family homes and multifamily properties alike. Eligibility runs through third-party certification: a unit generally has to meet ENERGY STAR or Zero Energy Ready Home program requirements, verified by an accredited rater, with a higher credit tier available for multifamily projects that meet prevailing wage requirements. Like 179D, 45L has been extended and reshaped by Congress multiple times since it first appeared in the mid-2000s.
Both programs adjust their exact dollar values periodically and depend on performance tiers, wage compliance, and certification pathways. So rather than quote a specific per-square-foot or per-unit figure here that may already be out of date by the time you read this, talk to a qualified tax professional about the current amount your project's performance tier would actually generate. What matters more for planning purposes is the framework: the better your building performs against the baseline, and the more of the compliance boxes you check, the larger both incentives get.
The Deadline Most Developers Haven't Priced In Yet
Here's the part of this story that's changed recently, and that a lot of teams are still catching up on: the One Big Beautiful Bill Act, signed into law in July 2025, moved up the expiration date for both programs. According to the IRS's own guidance on the law, 179D is no longer available for commercial projects that begin construction after June 30, 2026, and 45L is no longer available for residential units acquired (sold or first leased) after that same date.
The two programs are grandfathered differently, and the difference matters:
179D is tied to when construction begins. If your project met the beginning-of-construction test on or before June 30, 2026, it can still qualify for the deduction regardless of when the building is actually completed.
45L is tied to when the unit is acquired: the sale closing for a for-sale home, or the first lease for a rental unit. A multifamily project that broke ground years ago but leases up its units after June 30, 2026, does not get grandfathered in the way a 179D project does.
If your project is already in construction or close to lease-up, that timing detail is worth confirming immediately, not at tax time next year. If your project hasn't started construction yet, these two specific federal incentives are effectively off the table under current law, which makes it more important, not less, to know what state and utility incentive programs are still stacking on top. Those programs vary by jurisdiction, don't share this expiration date, and are exactly the kind of thing a one-time PDF report from eighteen months ago won't reflect.
That's the real lesson buried in this timeline: federal energy incentive policy moves fast, and it has reversed course before. Treating an incentive analysis as a one-time checkbox, done once at the start of a project and never revisited, is how developers end up either missing a deadline or missing a new program that opened up after their consultant's report was filed.
How Buildwiser Keeps Incentive Eligibility Current, Not Frozen in Time
A traditional energy consultant runs a compliance model, delivers a report, and moves to the next job. Figuring out which incentive programs a project actually qualifies for (federal, state, or utility) is a separate analysis that most development teams never commission at all, and even when they do, it reflects the rules on the day it was written.
Buildwiser AI builds incentive-program knowledge directly into every simulation, not as a one-time add-on. Every model run includes an analysis of which programs a project currently qualifies for, what that value looks like given the project's performance tier, and what specific design changes would open up additional programs or increase the benefit, checked against the rules as they stand today, not the rules as they stood when a report was filed months or years ago.
That's a meaningful distinction given what just happened to 179D and 45L. A static report can't tell you your incentive assumptions went stale. A platform that regenerates the analysis against current program rules can. And because Buildwiser is already running the energy simulation your project needs for code compliance in the first place, the incentive analysis isn't an extra engagement bolted on afterward. It's part of the same output, at the same speed.
The broader point holds regardless of what Congress does next: the cheapest compliant design path isn't always the one that ignores what's on the table. Sometimes a slightly higher-performance spec pays for itself twice: once in the incentive itself, once in the utility savings that follow it for the life of the building.
Frequently Asked Questions
Can architects and engineers actually claim the 179D deduction themselves?
Yes, in a specific circumstance: when the building is owned by a government agency or another tax-exempt entity that can't use the deduction, the owner can allocate it to the designer of record: typically the architect, engineer, or design-build contractor responsible for the energy-efficient systems. On privately owned commercial buildings, the deduction generally goes to the building owner.
Can a project claim both 179D and 45L?
Generally no, because they apply to different property types: 179D to commercial buildings, 45L to residential dwelling units. A mixed-use project could potentially see 179D applied to its commercial square footage and 45L applied to its residential units, but that requires a careful, project-specific analysis rather than an assumption either way.
Do I still qualify for 179D or 45L if my project hasn't started construction yet?
Under current law following the One Big Beautiful Bill Act, 179D is not available for commercial projects that begin construction after June 30, 2026, and 45L is not available for residential units acquired after that date. If your project is still in planning, these two specific federal programs are unlikely to apply, though state and utility incentive programs may still be worth pursuing.
What certification does a project need to qualify for 45L?
Units generally need to meet ENERGY STAR or DOE Efficient New Homes (formerly Zero Energy Ready Home) program requirements, verified by an accredited third-party rater, as part of the documentation required to support the credit.
See What Your Project Qualifies For
Incentive rules change fast, and a report that's accurate today can be stale in a year, which is exactly what just happened to two of the biggest federal energy incentives in the industry. Run your numbers against the rules as they actually stand right now.