A newly constructed office and a fifty-year-old warehouse renovation can both raise Section 179D questions. The useful distinctions are what property was installed, when construction began, when the property was placed in service, which technical route applies, and who may claim.
Do not confuse the current-law June 30, 2026 construction-start cutoff with a placed-in-service deadline. A project that begins construction by the cutoff may enter a conditional pipeline even if it is completed later, subject to all other requirements.
New construction
A whole new building still requires system-level evidence
New construction often offers coordinated lighting, HVAC, hot-water, envelope, controls, and commissioning records. That can improve documentation, but it does not make qualification automatic.
The ordinary route compares the proposed building with the applicable reference building using qualified software and the governing standard. Eligible cost, certification, labor treatment, and claimant rules remain necessary.
Project-type comparison
Different projects can reach a Section 179D review through different facts.
| Review point | Evidence or measure | Why it matters |
|---|---|---|
| New construction | New building systems | Coordinate reference model, installed systems, service, and certification. |
| System renovation | New property in existing building | Map installed scope, whole-building model, cost, and existing context. |
| Qualified retrofit plan | Alternative route | Assess measured EUI requirements and separate certification timing. |
Renovation
An existing building can contain newly installed qualifying property
A renovation may replace lighting, HVAC, envelope components, or several systems. Identify the installed scope, cost, service date, and condition of the rest of the building. A renovation label does not determine which pathway or amount applies.
For the ordinary route, the model still addresses whole-building annual energy cost. Existing conditions can affect inputs and evidence, but they do not turn the test into a product-level savings calculation.
Dates
Use three date fields instead of one project year
Track construction start for cutoff analysis, placed in service for when property becomes ready and available, and the relevant return or filing date for tax procedure. A project’s marketing completion date may not answer any of those questions precisely.
Preserve dated contracts, permits, site records, invoices, commissioning and acceptance records, and occupancy or activation evidence. The tax adviser should assess their significance under the applicable rules.
Three dates, three purposes
Keeping the clocks separate prevents false deadlines.
Construction start
Current-law cutoff
Placed in service
Ready and available
Tax return
Reporting procedure
Retention
Support the position
Path selection
The alternative retrofit route has a different measurement structure
Current Section 179D includes an alternative deduction for certain energy-efficient building retrofit property. It uses a qualified retrofit plan, measured energy-use intensity reduction, and a certification timeline that differs from the ordinary modeled route.
Do not blend the ordinary 25% modeled annual-energy-cost threshold with the retrofit route’s measured EUI test. A project team should select and document the applicable pathway rather than borrowing the more favorable feature of each.
Illustrative renovation scope
Area percentages describe the hypothetical project, not tax allocation.
Hypothetical area
Hypothetical zones
Hypothetical surface area
| Item | Value | Note |
|---|---|---|
| Lighting area renovated | 70% | Hypothetical area |
| HVAC zones renovated | 45% | Hypothetical zones |
| Envelope area renovated | 20% | Hypothetical surface area |
Prepare the review
Classify the property and pathway before modeling
- New construction or existing-building scope
- Installed lighting, HVAC/hot-water, and envelope property
- Construction-start evidence
- Placed-in-service evidence
- Ordinary or alternative retrofit pathway
- Applicable reference standard or retrofit-plan requirements
- Qualified software or measured-EUI records
- Inspection and certification timeline
- Eligible cost and prior deductions
- Claimant, allocation, and filing treatment
Continue the review
Common questions
Practical answers before the review
Is Section 179D limited to new buildings?
No. Improvements to existing buildings may also warrant review under the applicable rules.
Must a qualifying project be placed in service by June 30, 2026?
That is not the current-law cutoff. The statute addresses property whose construction begins after June 30, 2026.
Are ordinary and retrofit tests interchangeable?
No. They use different structures and should be evaluated separately.