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

What Congress did in the One Big Beautiful Bill Act (Public Law 119-21) was close the door on new work. The law ends the deduction for property “the construction of which begins after June 30, 2026.” Anything that started earlier is still eligible. The owners I talk to hear the word “terminated” and assume the whole thing is gone. For a mechanical or sheet metal contractor, three areas are still worth real money: the jobs you’re building now, the systems you designed for public buildings over the last few years, and the payroll records that determine how large the deduction will be.

Where Mechanical Work Fits Into 179D

Qualifying property has to be installed as part of interior lighting; heating, cooling, ventilation, and hot water systems; or the building envelope. The 25 percent is measured across those systems combined, using an energy model that compares the building with the ASHRAE 90.1 reference building.

Mechanical scope sits in the middle of that model: air handlers, chillers, boilers, ductwork, controls, and water heaters. The deduction is calculated using specifications your shop helped write or install.

For tax years beginning in 2026, the IRS instructions for Form 7205 put the deduction at $0.59 to $1.19 per square foot, depending on energy savings, and as high as $5.94 per square foot when prevailing wage and apprenticeship rules are met. Those are deduction amounts. What they’re worth in cash depends on the claimant’s tax bracket. Earlier years have their own rates. Every claim also needs certification from a licensed engineer or contractor who isn’t related to the taxpayer, and that person has to inspect the building after the property is placed in service.

Projects Underway: Your Job File Is the Evidence

Eligibility turns on the day construction began. Opening day doesn’t matter. A school renovation that started in May 2026 and wraps up in 2028 can still qualify, and the owner claims the deduction for the year the building is placed in service.

Owners whose start dates fell close to June 30 will have to prove when work began, and much of that proof is sitting in your job files: signed contracts, permits, purchase orders, delivery tickets, daily logs, and the first pay application. Keep those records together, and keep them for a long time. How the start date is measured on a particular project is a call for the owner’s tax professional, who can’t make it without your paperwork.

When the Contractor Is the Designer

This is the part most mechanical contractors miss.

Governments don’t pay income tax, so a county or school district can’t use the deduction. Neither can a tribal government or a tax-exempt organization such as a nonprofit hospital, university, or church; those two categories were added for property placed in service after 2022. The law lets these owners allocate the deduction, in writing, to the person primarily responsible for designing the property.

IRS Notice 2008-40 defines a designer as “a person that creates the technical specifications for installation of energy-efficient commercial building property,” and it names contractors alongside architects and engineers. It also draws a hard line: “A person that merely installs, repairs, or maintains the property is not a designer.”

So look at what your shop actually did on each job. Installing to someone else’s drawings on a plan-and-spec job puts you on the installer side of that line. Running a design-build mechanical package for a county courthouse or nonprofit hospital, where your team wrote the technical specifications, may make you the designer to whom the owner can allocate the deduction.

Designers Work Against a Shorter Clock

An owner who missed 179D can usually catch up on a current return by filing for an accounting method change. Designers don’t get that option. A designer claims the deduction for the year the property was placed in service, which means amending that year’s return while it’s still open – generally three years from the date the original return was filed. On a job placed in service in 2023, the window probably closes sometime in 2027, depending on when that year’s return was filed. Every year you wait, another year of projects falls off.

Prevailing Wage Records Can Multiply the Deduction

The top rate requires that “any laborers and mechanics employed by the taxpayer or any contractor or subcontractor in the installation” be paid prevailing wages, with apprenticeship rules on top. That requirement reaches every subcontractor on the job, including your company. Whoever claims the deduction will come asking for certified payroll records and apprentice hours. Have them ready, and you’re the contractor that owner wants on the next bid.

What to Do This Quarter

Pull every public, tribal, and nonprofit job placed in service since about 2023 for which your shop wrote the mechanical design.

Ask each owner whether 179D has already been allocated to someone.

For any job that broke ground near June 30, 2026, gather the start-of-construction paperwork now, while people still remember the dates.

Store certified payroll and apprenticeship records in the job file.

Call your tax professional before you call the owner. Whether a given project qualifies comes down to its facts.

My father, a CPA, told me that tax evasion is a crime, but tax avoidance is mandatory. Congress wrote 179D for exactly these buildings, and mechanical contractors did a lot of the work that earned it. Start with the design-build jobs. They’re the ones on a clock.