179D After the Cutoff: What Mechanical and Sheet Metal Contractors Can Still Claim

A federal tax break tied to energy-efficient commercial buildings changed recently, and while it's aimed at building owners and contractors rather than individual homes, it's worth knowing about if you own or help manage a commercial property, church, or nonprofit building. The deduction, called Section 179D, has existed since 2006 for commercial buildings that cut energy use in lighting, heating and cooling systems, or insulation by at least 25 percent compared to a standard reference building. Under a new law, construction that starts after June 30, 2026, no longer qualifies. But projects that broke ground before that date can still claim it, even if they're finished later.

This matters most for owners of public, tribal, or nonprofit buildings, since those organizations don't pay income tax and can't use the deduction themselves. Instead, they can formally assign it to whoever designed the building's energy systems. If you're involved with a nonprofit or community building project, it's worth asking whether this deduction has already been claimed or assigned to someone.

There's also a time limit: claims for a building already in use generally have to be filed within three years of the original tax return for that year, so older projects can age out of eligibility. The size of the deduction also depends on paperwork showing fair wages were paid during installation. None of this applies to typical home upgrades, but it's useful context if your household touches a commercial or nonprofit building project.