There is not much published NYC data yet, because ADU applications only opened on September 30, 2025. One NYC ADU developer, Unit Two Development, has estimated that backyard ADUs and garage conversions could start at $300,000 to $400,000, depending on size and complexity. Your lot, the ADU type and the required safety systems set the real number.
What published figures exist?
| Item | Published figure, as of October 2026 | Source |
|---|---|---|
| Backyard ADU or garage conversion | Could start at $300,000 to $400,000 | Unit Two Development founder, via Business Insider (reported January 2026) |
| Basement or cellar ADU | No reliable NYC figure found | Regulations were still being finalized when early cost reports ran |
| Attic ADU | No reliable NYC figure found | Not covered |
| Plus One financing cap | Up to $395,000 per property, combined | HPD Plus One ADU FAQ |
The financing cap is not a cost estimate, but it gives a sense of the project sizes the city expected.
What goes into the price?
HPD's ADU guidebook splits the budget into two groups:
- Soft costs: surveyor, registered design professional and engineering fees, permits, insurance, testing, temporary utilities and a possible property tax increase.
- Hard costs: materials, the general contractor, excavation, utility hookups, mechanical, electrical and plumbing labor, demolition, site work, sprinklers and attic work.
What makes NYC ADUs expensive?
- Sprinklers. DOB requires them in detached, attic and cellar ADUs.
- Egress and fire separation. Cellars need two independent exits; units near lot lines need rated walls.
- Utilities. Extending water, sewer and power to the back of a lot or into a cellar.
- Access. Getting materials through a narrow side yard.
- Flood work. Elevating an above-grade unit in a flood area.
Why one number is not enough. It depends on the building you start with. A sound garage with a short utility run is a different job from a cellar that needs a second exit dug out. We price your project in a written, itemized quote after a site visit.
Sources, as of October 2026:
- Construction Owners, "NYC legalizes backyard tiny homes but costs remain a hurdle" (January 2, 2026), reporting Business Insider.
- NYC HPD, Plus One ADU FAQ and ADU guidebook.
- NYC DOB, ADU FAQs. Figures are published estimates, not our quotes.