Step-by-Step Guide

NYC ADU Permit Process

From feasibility check to Certificate of Occupancy — here is every step, cost, and document you need to build a legal ADU in New York City.

1

Feasibility Check

Self / HPD

Verify your property is eligible for an ADU by checking zoning district, lot size, building type, and any overlays (flood zones, historic districts). You can use the free tool on nycadu.com or HPD’s online eligibility screener.

Free
1–2 weeks

Documents Needed

  • Property address and BBL (Borough-Block-Lot)
  • Current Certificate of Occupancy
  • Property deed (confirming ownership)
Start with our free eligibility checker for an instant assessment before hiring anyone.
Even if your property passes the initial check, a licensed architect should confirm feasibility during design.
2

Hire a Design Professional

Private (RA/PE)

Engage a NYS-licensed Registered Architect (RA) or Professional Engineer (PE) to design your ADU. You can save significant time and money by using HPD’s Pre-Approved Plan Library (PAPL) instead of a fully custom design.

$8K–$20K custom, less with pre-approved
4–8 weeks custom, 2–4 weeks pre-approved

Documents Needed

  • Signed contract with your architect/engineer
  • Preliminary design drawings
  • Pre-approved plan selection (if using PAPL)
Ask if they have ADU experience—the NYC ADU code is new and not all architects know it well.
Pre-approved plans can cut design costs by $15K–$40K and shave weeks off the timeline.
Verify your architect is registered with the NYC DOB as a Registered Design Professional (RDP).
3

Site Survey & Engineering

Private (Licensed Surveyor / Geotech)

Conduct a property survey, soil/geotechnical testing, and for basements, radon and chemical vapor testing. These reports inform the structural and foundation design.

$1K–$3.5K
1–2 weeks

Documents Needed

  • Property/boundary survey
  • Soil/geotechnical report
  • Radon test results (basement/cellar ADUs)
  • Chemical vapor intrusion assessment (if required)
Order the survey early—it’s needed before your architect can finalize site plans.
Soil testing is especially important for detached ADUs; poor soil can add $20K+ to foundation costs.
Radon testing is required for all below-grade habitable spaces in NYC.
4

DEP Sewer Certification

NYC DEP

The NYC Department of Environmental Protection (DEP) must certify that the local sewer system has capacity for your new unit. Your PE or RA files this on your behalf.

Included in design fees
5–6 business days

Documents Needed

  • DEP sewer certification application (filed by PE/RA)
  • Site drainage plan
  • House/site connection proposal
DEP turnaround has been consistently fast—don’t let this step hold up the rest of your timeline.
If you’re in a combined sewer area, discuss stormwater management with your engineer early.
5

File with DOB NOW

NYC DOB

Submit your application through the DOB NOW: Build portal. Basement and garage conversions use the Alt-CO-GC (Alteration CO – General Construction) work type. New detached ADUs file as a New Building application.

$130+ filing fee, $1K–$10K total fees
Same day (filing)

Documents Needed

  • Completed DOB NOW application (PW1 form equivalent)
  • Architectural plans stamped by RDP
  • Structural calculations
  • All Phase 1–3 documents uploaded
  • Owner authorization / signature
  • Filing fee payment
Double-check every upload before submitting—missing documents trigger objections that add weeks.
Your architect should handle the filing, but review the application yourself before they submit.
Filing fees vary by scope: simple conversions are cheapest, new buildings are most expensive.
6

DOB Plan Examination

NYC DOB

DOB examiners review your plans for code compliance, zoning conformance, and structural adequacy. Pre-approved plans undergo a streamlined review that cuts the timeline roughly in half.

Included in filing fees
4–8 weeks (conversions), 8–16 weeks (new build)

Documents Needed

  • No new documents (DOB reviews what was filed)
  • Responses to any examiner objections
  • Revised plans if objections require changes
Pre-approved plans cut review time by ~50% since the design is already vetted.
Each objection round adds 2–4 weeks. A good architect minimizes these by filing clean applications.
You can track status in real-time on the DOB NOW portal using your application number.
7

Permit & Construction

NYC DOB / Private GC

After plan approval, obtain your work permit and begin construction. You’ll need a licensed General Contractor (GC) and potentially separate permits for plumbing, electrical, and mechanical work.

Permit fees $2K–$15K; Construction: see cost table below
3–6 months (basement), 6–12 months (detached)

Documents Needed

  • DOB-approved work permit
  • General Contractor license and insurance
  • Subcontractor licenses (plumbing, electrical, etc.)
  • Construction schedule and safety plan
Get at least 3 bids from licensed, insured GCs with ADU or NYC residential experience.
Basement conversions are faster and cheaper since the shell exists. Detached ADUs need foundation, framing, and full build-out.
Build in a 15–20% contingency budget for unexpected issues (especially in older homes).
8

Inspections

NYC DOB

DOB inspectors visit at key milestones: foundation, framing, rough-in (plumbing/electrical/mechanical), fire safety systems, and a final inspection. All must pass before you can get your Certificate of Occupancy.

$500–$1.5K for special inspections
Throughout construction

Documents Needed

  • Inspection request (scheduled 48+ hours in advance)
  • Approved plans on-site for inspector reference
  • Special inspection reports (structural, fire, etc.)
  • TR-1 progress inspection forms
Schedule inspections at least 48 hours in advance—DOB inspectors are busy.
Never cover up work (walls, ceilings) before the rough-in inspection passes.
Your GC should coordinate inspections, but verify they’re actually happening on schedule.
9

Certificate of Occupancy

NYC DOB

After all inspections pass, DOB issues an updated Certificate of Occupancy reflecting the ADU. This is the final legal step—without it, you cannot legally occupy or rent the unit.

$1K–$3.5K
2–4 weeks after final inspection

Documents Needed

  • Final inspection sign-off (all trades)
  • Letter of completion from architect
  • Updated CO application
  • As-built drawings (if changes from approved plans)
Do not move tenants in or list the unit for rent until the CO is issued.
Keep all permits, inspection reports, and the CO in a safe place—you’ll need them if you ever sell.
The CO is your proof that the ADU is 100% legal. It’s what makes your rental income legitimate and your property value increase real.

Total Cost Summary by ADU Type

All-in estimates including design, permitting, construction, and inspections.

Basement Conversion

$100K–$250K

Converting existing basement/cellar space into a legal dwelling unit

Garage Conversion

$150K–$300K

Converting an existing garage into a habitable ADU

Backyard Cottage (Detached)

$250K–$400K+

New detached structure built in your backyard or side yard

Ready to start your ADU project?

Check if your property qualifies in under 2 minutes, or book a consultation to walk through the process with an ADU specialist.

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