NYC ADU Permit Process: A Step-by-Step Guide

You've decided to build an ADU. You know your property is eligible, you've got a general idea of what you want to build, and you're ready to get started. Now comes the part that intimidates most NYC homeowners: the permit process.

The good news is that NYC's ADU permitting system, while not simple, is more streamlined than many homeowners expect — especially if you use a pre-approved plan. The bad news is that there are real costs at every stage, multiple agencies involved, and mistakes that can set you back months.

This guide walks you through all nine steps from initial feasibility assessment to certificate of occupancy, with real costs and timelines at each stage.

Before you start: what you need to know

NYC began accepting ADU applications on September 30, 2025, through the DOB NOW: Build filing portal. The process is governed by Local Laws 126 and 127 of 2024, which were part of the City of Yes for Housing Opportunity initiative. All ADU applications must be filed by a Registered Design Professional (RDP) — either a licensed architect or professional engineer registered in New York State.

You cannot file an ADU application yourself. You need a professional. That's step one, and it's non-negotiable.

Step 1: Feasibility assessment

Timeline: 1-2 weeks
Cost: $0 - $3,000

Before you spend real money on design and engineering, you need to confirm that your property actually qualifies for an ADU and what type of ADU makes sense. This involves three checks:

• Zoning verification: Confirm your property is in an eligible zoning district (R1 through R5, excluding R1-2A, R2A, and R3A unless in the Greater Transit Zone). The city's online ADU feasibility tool can give you a preliminary answer.
• Flood zone check: Determine if your property is in a FEMA Special Flood Hazard Area, Coastal Flood Risk Area, or DEP 10-Year Rainfall Flood Risk Area. If so, subgrade ADUs are prohibited.
• Lot and building analysis: Review your lot dimensions, existing building footprint, rear yard depth, and setback distances. This determines whether a backyard cottage is feasible and what size ADU your lot can support.

You can start this process for free using the city's online tools. For a professional feasibility assessment from an architect, expect to pay $1,500 to $3,000. This is money well spent — it prevents you from investing in design for a project that can't be built.

Step 2: Choose your path — custom design vs. pre-approved plans

Timeline: 1 day (pre-approved) to 4-8 weeks (custom)
Cost: $0 (pre-approved selection) to $8,000 - $20,000 (custom design)

This is a critical decision point. NYC offers two paths to an ADU permit:

Option A: Pre-Approved Plan Library (PAPL)

DOB has created a library of pre-approved ADU designs that have already been reviewed and approved for code compliance. If you choose one of these plans, the design review portion of your permit application is significantly streamlined — DOB only needs to verify that the pre-approved design works on your specific site, not review the entire design from scratch.

Advantages: faster permitting (DOB reviews site-specific conditions only), lower design costs (you're selecting, not designing from scratch), and reduced risk of plan examination rejections.

Limitations: the designs may not perfectly match your lot conditions or aesthetic preferences, and your RDP still needs to prepare site-specific drawings showing how the pre-approved plan fits your property.

Option B: Custom design

You hire an architect to design an ADU specifically for your property. This gives you maximum control over layout, aesthetics, and optimization for your lot, but it takes longer, costs more, and faces more scrutiny during plan examination.

For a custom ADU design, expect to pay an architect $8,000 to $20,000 depending on the complexity of the project. This includes schematic design, design development, construction documents, and filing drawings.

Step 3: Site-specific engineering and documentation

Timeline: 2-4 weeks
Cost: $3,000 - $8,000

Whether you chose a pre-approved plan or custom design, your RDP needs to prepare site-specific documentation. This includes:

• Site survey: A licensed surveyor documents your lot dimensions, existing structures, elevations, and property boundaries. Cost: $1,500 - $3,000.
• Structural engineering: If your ADU involves modifications to the existing structure (basement conversion, attic conversion) or new construction (backyard cottage), you'll need a structural engineer's stamp. Cost: $1,500 - $4,000.
• Utility planning: Documentation of water, sewer, electrical, and gas connections for the new unit.
• Energy code compliance: All new construction and major renovations must meet NYC Energy Conservation Code requirements.

Step 4: DOB NOW filing

Timeline: 1-2 days for filing; 2-8 weeks for initial review
Cost: $130 minimum filing fee (scales with project value)

Your RDP files the application through DOB NOW: Build using their NYC.ID account. The filing type depends on your project:

• Basement/attic conversion: Filed as an Alteration-CO-GC (Alt-CO-GC) job, since you're changing the certificate of occupancy of an existing building.
• New backyard cottage: Filed as a New Building-GC job.

In the PW1 (Plan/Work Application) tab, there's a dedicated Ancillary Dwelling Unit section under Filing Review Type. Your RDP must indicate:

• Whether the scope of work includes an ADU
• Pre-approved plan number (if using PAPL)
• ADU location (basement, attic, backyard, etc.)
• Where the main entrance opens

The minimum filing fee is $130 as of 2026, up from $100 for most work types. The actual fee is calculated on a sliding scale based on your project's total construction cost. For a typical ADU project valued at $100,000 to $250,000, expect filing fees in the range of $1,000 to $3,000.

Under Local Law 128 of 2024, you must now pay at least 50% of the total permit fee upfront (minimum $130) for work that results in a new or amended certificate of occupancy. The remainder is due before permit issuance.

Step 5: Plan examination

Timeline: 4-12 weeks (pre-approved plans on the faster end)
Cost: included in filing fees (but corrections cost time)

This is where DOB reviews your plans for compliance with the building code, zoning resolution, and ADU-specific rules. The examiner checks everything: structural adequacy, fire protection, egress, light and air, energy code, accessibility, and ADU-specific requirements like water sensors and entrance identification.

For pre-approved plans, the examination focuses on site-specific conditions: does the pre-approved design actually fit on your lot? Are setbacks met? Is the rear yard coverage within the 33% limit? This is faster than a full plan examination.

For custom designs, the examination is comprehensive. Every aspect of the design is reviewed against code requirements. This is where most delays happen.

Common reasons for plan examination objections

• Setback violations: The ADU doesn't meet required distances from property lines
• Rear yard coverage: Backyard cottage exceeds 33% of required rear yard
• Ceiling height non-compliance: Basement doesn't meet minimum ceiling height
• Inadequate egress: Exit paths don't meet code requirements
• Missing fire protection: Sprinkler or firewall requirements not addressed
• Flood zone conflicts: Subgrade unit in restricted flood area

Each round of objections adds 2-4 weeks to your timeline as your RDP revises plans and resubmits. This is the single biggest source of delays in the ADU process.

Step 6: Permit issuance

Timeline: 1-2 weeks after approved plans
Cost: remainder of permit fees (50% balance)

Once your plans pass examination, DOB issues your work permit. At this point, you pay any remaining permit fees. Your total permit costs for a typical ADU project (including filing fees, plan examination fees, and permit issuance) will typically range from $2,000 to $6,000, scaled to the construction value of the project.

With permit in hand, you can begin construction. But there are conditions: you must post the permit at the construction site, work must begin within 12 months, and all work must comply with the approved plans.

Step 7: Construction

Timeline: 3-9 months (basement conversion on the shorter end; new construction longer)
Cost: your construction budget ($60,000 - $300,000+)

Construction is obviously the most variable phase. A few NYC-specific considerations:

• Licensed contractors: All work must be performed by or under the supervision of NYC-licensed contractors. Plumbing and electrical work require separate licensed professionals.
• After-hours work: NYC has strict noise regulations. Residential construction is generally limited to weekdays 7 AM to 6 PM. Plan accordingly.
• Neighbor notification: While not always legally required, informing your neighbors about the project is strongly recommended. ADU construction can be disruptive, and neighbor complaints can trigger DOB inspections.
• Interim inspections: DOB may require inspections at various stages — foundation, framing, rough plumbing/electrical, insulation, and final. Your contractor should coordinate these.

Step 8: Final inspection

Timeline: 2-6 weeks (scheduling + inspection + any corrections)
Cost: inspection fees typically included in original permit costs

When construction is complete, your contractor requests a final inspection from DOB. An inspector visits the site and verifies that the completed work matches the approved plans and meets all code requirements. They'll check:

• Structural integrity and compliance with approved plans
• Fire protection systems (sprinklers, smoke/CO detectors, fire-rated assemblies)
• Egress compliance (exits, windows, door hardware)
• Plumbing and electrical systems
• Water sensors and flood mitigation (for basement units)
• ADU entrance identification and separation from main dwelling
• Energy code compliance

If the inspector finds deficiencies, you'll need to correct them and schedule a re-inspection. Each round of corrections adds 2-4 weeks.

Step 9: Certificate of occupancy

Timeline: 2-4 weeks after passing final inspection
Cost: CO application fee (typically $100 - $200)

The final step is obtaining an amended certificate of occupancy (for conversions) or new certificate of occupancy (for new construction) that reflects the ADU. This document legally authorizes occupancy of the new unit.

For existing buildings adding an ADU, you'll receive an amended CO that changes the building's use designation — for example, from a two-family dwelling to a three-family dwelling (since adding an ADU to a two-family home creates a three-family building under the State Multiple Dwelling Law, unless separated by a firewall).

Once you have the CO, your ADU is legal. You can rent it out, move family in, or use it however the CO permits.

Total costs and timeline summary

Costs by phase

• Feasibility assessment: $0 - $3,000
• Design (pre-approved path): $2,000 - $5,000 for site-specific adaptation
• Design (custom path): $8,000 - $20,000
• Site survey and engineering: $3,000 - $8,000
• DOB filing and permit fees: $2,000 - $6,000
• Construction: $60,000 - $300,000+
• Certificate of occupancy: $100 - $200
• Total soft costs (excluding construction): $7,000 - $37,000

Timeline ranges

• Best case (pre-approved plan, basement conversion, no objections): 6-8 months total
• Typical case (pre-approved plan with minor site issues): 8-12 months
• Complex case (custom design, new construction, plan objections): 12-18 months

Common pitfalls and how to avoid them

1. Filing without a thorough feasibility check: Spending $10,000+ on design before confirming your lot actually qualifies is the most expensive mistake homeowners make. Always start with feasibility.
2. Underestimating the RDP's role: Your architect or engineer is your quarterback through this process. Hire someone with NYC ADU experience, not just any licensed professional.
3. Ignoring the flood zone check: Filing for a basement ADU in a flood zone is an automatic rejection. Check first.
4. Skipping the pre-approved plan option: Unless you have very specific design needs, pre-approved plans save significant time and money. At minimum, review the library before committing to custom design.
5. Not budgeting for soft costs: Homeowners consistently underestimate the cost of design, engineering, surveying, and permits. Budget $15,000 to $30,000 for these costs on top of construction.
6. Choosing a contractor without DOB experience: NYC construction is different from suburban construction. Your contractor needs to know DOB inspection processes, scheduling requirements, and code specifics.

The NYC ADU permit process is manageable, but it rewards preparation and punishes shortcuts. Do your homework on feasibility, hire experienced professionals, consider pre-approved plans, and budget for the full cost — including the soft costs that many homeowners forget. The process takes time, but at the end of it, you have a legal, code-compliant unit that generates income and adds value to your property.