Insights · Tax strategy · September 2026

What changed in tax law this year: two incentives wound down, two got stronger

Federal legislation enacted in July 2025 reshaped the incentive landscape for 2026, changing what is worth claiming and when.

Two long-standing energy-efficiency provisions, the Section 179D deduction and the Section 45L credit, wound down this year under federal legislation enacted in July 2025 (Public Law 119-21). The same legislation restored two things that matter even more for many organizations: immediate expensing for domestic research costs, and permanently restored 100% bonus depreciation. Here is what changed and what it means for owners, developers, designers and the CPAs who advise them.

Here's what changed

Section 179D deduction: winds down for property whose construction begins after June 30, 2026. Property that began construction on or before that date falls under the statutory transition rule, so existing and transition projects require date-specific review; this is not a blanket completion deadline.
Section 45L credit: wound down for homes acquired after June 30, 2026.
Domestic R&D expensing: fully restored, with no more forced amortization.
Bonus depreciation: 100%, permanently restored.

What it means

If you own or are building commercial or multifamily property

Cost segregation has always been one of the most effective ways to accelerate depreciation on a building. With 100% bonus depreciation now permanently restored, that advantage is bigger than ever: a study identifies the components of a property that qualify for shorter depreciation lives, then puts real numbers behind the deductions your organization can claim now instead of over decades. If you are renovating, a partial asset disposition study documents what was removed, not just what went in.

If you have a 179D or 45L project in flight

Dates decide everything. Construction-start and placed-in-service records determine whether a project falls inside the transition rule, so screening those dates is the first step on any 179D or 45L question. Designers of government, nonprofit and Tribal buildings should ask the same question about allocations before assuming an opportunity has closed — or that it is still open.

If your company does research and development

Domestic research costs are immediately deductible again. Manufacturers, technology and life-science companies should revisit how they document qualifying activities, technical uncertainty and experimentation, because the credit and the expensing rules now work together rather than against each other.

If you advise clients

Incentive programs shift. What doesn't change is the need for a strategy built on current law, not last year's playbook. Green Summit works alongside accounting and advisory firms with engineering-backed studies and substantiation; final filing decisions stay with you and your client.

Frequently asked questions

Has 179D ended for every project?

No. The construction-start cutoff applies to property whose construction begins after June 30, 2026. Existing and transition projects require date-specific review; it is not a blanket completion deadline.

Does 100% bonus depreciation mean a cost segregation study always produces cash savings?

Not automatically. Tax position, loss limitations, elections and future disposition plans affect the benefit, and your tax advisor determines the return position. What a study does is give that decision engineering-grade evidence.

Not sure how these changes affect your organization?

That's exactly the kind of question we're built to answer. Tell us who you are and what you own, build or design.

Information reviewed September 22, 2026. This article is general information, not tax advice; eligibility and each claimant's records are evaluated for the specific project.

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