An NYC ADU’s energy-code edition can depend on its filing history, not only its unit type. The Department of Buildings (DOB) moved to the 2025 New York City Energy Conservation Code (NYCECC) on March 30, 2026. A filing date by itself may not settle the transition for an earlier application.

Check the filing and energy analysis

The current DOB NYCECC Frequently Asked Questions says complete energy submissions filed on or after March 30, 2026 must comply with either the 2025 NYCECC or 2025 NYC ASHRAE 90.1. Complete submissions filed before March 30 generally remain under the 2020 NYCECC only if the submission was complete and diligently pursued and there is no material compliance change or post-date change from a prescriptive path to a modeling path. DOB’s March 2026 follow-up notice separately says new job filings, filings with incomplete energy analysis, and historic-building alterations must comply with the 2025 NYCECC from March 30. A prior submission date alone does not establish that the 2020 code still applies.

For an existing application, assemble the submission receipt, the energy-analysis package and its status, evidence that the filing was diligently pursued, the selected compliance path, and the history of material design or compliance changes. Ask the design professional and DOB to confirm the edition before relying on an earlier submission. The current DOB Energy Conservation Code page and service updates provide the City’s current transition information.

Include historic-building status

The City’s March 2026 notice also identifies alterations of historic buildings as subject to the 2025 NYCECC. It says the energy submission must include a Historic Building Report; the earlier general exemption no longer applies under this transition. Confirm the building’s historic status, the proposed alteration, and the required filing documents with DOB. A building’s historic status does not determine whether an ADU is eligible or what its complete technical design requires.

Keep the transition separate from the ADU type review

The transition does not answer whether a proposed basement, cellar, above-grade, detached, or manufactured ADU is eligible, how it is classified, or which energy-code provisions apply to its work. Use DOB’s current 2025 NYCECC text and obtain project-specific review of filing status, energy analysis, changes, historic status, and technical requirements. The City’s ADU type guide covers the separate typology questions.