The Costs of Building an ADU in NYC
Are you looking to build an ADU in New York City? Here’s how to plan your budget so no hidden surprises jump out along the way.
1. Permits
Before your ADU becomes legal to rent, you’ll need the proper permits:
DOB (Department of Buildings) filing fees: $500 – $2,000
Plumbing or electrical permit: $300 – $800 each
Fire sprinkler plan review (for cellar units): $600 +
Zoning verification: $250
Application for Certificate of Occupancy: $300 +
Who can help expedite: an architect or design & build firm experienced with NYC ADU projects. Many architects and designers offer ADU packages that include permit costs and coordination with reliable expediters.
2. Utility Upgrades You Never Saw Coming
Water, sewer, gas, and a 200-amp electrical service are all must-haves for an ADU. Common hidden utility costs include:
Electrical panel upgrades: $3,000 – $8,000
Replacing or upsizing water and sewer lines: $5,000 – $15,000
Extending a gas line: $2,000 – $6,000
Separate water meter (for rental units): $1,500 +
How to avoid it: Get a utility audit before breaking ground. Have a licensed plumber and electrician inspect what’s currently in place.
3. Code Requirements
NYC building codes are comprehensive. Make sure you check the following:
Ceiling height: Habitable cellar and basement spaces must be at least 7 ft high. Most cellars fall short, often requiring excavation or floor lowering.
Egress windows: Must be at least 5.7 sq ft, no more than 44 in off the floor, and open into a yard (not a shared alley).
Sprinklers: Most ADUs require sprinkler systems, adding $10,000 – $20,000 to your build.
Stairs & railings: For rooftop or second-story ADUs, stairs must meet code, often requiring structural changes.
If not compliant, your ADU won’t receive a Certificate of Occupancy, turning it into an extremely expensive storage unit.
How to avoid it: Request a code feasibility study before design begins. A skilled ADU expert or design professional can model your space to meet code and flag issues early.
4. Soil, Slope, and Site Surprises
That “flat” backyard? It might actually slope a full 12 in over 20 ft. Or perhaps the soil is dense clay or even hiding an old septic tank beneath the garage.
Common site-related costs:
Grading and drainage: $5,000 – $15,000
Foundation work on unstable soil: $10,000 +
Tree removal or root protection: $2,000 – $7,000
How to avoid it: Order a site survey and soil report before finalizing plans. Many NYC lots contain undocumented fill or old utility remnants. A $1,500 survey today can save $20,000 in change orders later.
5. The “Soft Cost” Avalanche
These are the invisible fees that pile up quickly:
Architectural and engineering fees: 10 – 15 % of construction cost
Title or survey updates: $1,000 – $2,500
Construction insurance: $500 – $1,500
Sidewalk sheds or temporary fencing: $3,000 – $8,000 (required for any work on the street side)
How to avoid it: Ask for an inclusive proposal from your design-build team that outlines every third-party fee. Always budget a 15 – 20 % contingency, not just 5%.