With the 179D deadline passed, what should building teams check now? / Our Blog / By Finulent Solutions June 30, 2026, passed, and many building owners, architects, and CPA companies are still wondering what changed. The deadline did not remove the deduction, it simply changed who still qualifies, and the essential question at this point is no longer “How do we meet the deadline?” It has changed to “Did the project qualify, and what needs to be confirmed now?” At Finulent Solutions, we collaborate with architectural companies, MEP consultants, general contractors, and CPA firms around the United States on energy performance modelling and 179D paperwork. What happened on June 30th? According to the Department of Energy’s summary of Section 179D, property placed under construction after June 30, 2026, under the One Big Beautiful Bill Act, is no longer in effect. It is not a completion test, rather, it is a construction start test. Projects that began construction on or before that date, either by completing the physical work test or by contributing at least 5% of the project’s total cost, remain in the game. Despite the energy efficiency of the design, projects that were not under construction on the date of this report are not. The duck curve is what drives the industry toward longer duration: peak generation around midday and peak demand in the evening. A 2-hr system catches the tail end of that gap, while a 4-hr system bridges it properly. The door hasn’t closed even if the deadline has passed In all the chaos, this is what a lot of people overlook. Certain projects that met the eligibility requirements before June 30 are still being assessed, certified, and claimed, sometimes years later. That eligibility was the issue, not the filing window. 179D is more of a mechanism to verify that the energy modelling, third-party certification, and Form 7205 reporting are all in place while a project is already underway. It’s proof that projects will probably lose the deductions they’ve already claimed simply because the paperwork wasn’t prepared for an IRS examination. This distinction is more significant than it appears on the surface. Many teams believe that once the deadline has passed, the relevant tax benefit is no longer valid. With 179D, that belief can come back to haunt a building owner if they fail to acquire a review indicating that there is an appropriate documentation trail. Looking Back Can Still Add Value This is a detail that is rarely acknowledged. There is no need to wait until the project’s end in 2026. For buildings constructed or remodelled since 2006 that did not claim the deduction, a lookback study on IRS Form 3115 can be used to claim the deduction without having to modify previous returns. This is something that many building owners are ignorant of. In many circumstances, Section 179D only becomes apparent after it is clearly mentioned. This is frequently the larger, more discreet transaction for a firm with a portfolio of older commercial buildings, as opposed to any tied to the June deadline. Keep an eye on the legislative side too A bill is being considered that should be closely monitored. In April 2026, a bipartisan bill called the American Energy Dominance Act was filed, with the intention of making Section 179D a permanent deduction with no sunset date. It has not yet expired and remains in effect, but it does indicate a desire in Congress to reverse this. Anyone planning a project should monitor it rather than simply following the guidelines. Why do you need a modelling and documentation partner? Nothing changes the fact that a 179D claim must include an authorized energy model, competent third-party certification, and paperwork indicating a construction start date and connection to the claim. That is true whether the project began in May or the claim is based on a retrofit that occurred ten years ago. Most design or MEP firms don’t typically have this kind of specialized capacity on staff, and most CPA firms don’t either. Energy performance modelling using DOE-approved tools, IRS-supported documentation, working with the engineer of record, and a claim that can stand up for a project that occurred as recently as June 30 or as far back as 2006 are the areas in which we operate. The deadline affected who was eligible. It did not modify the level of diligence required for a 179D claim.
