Second Key NYC: ADU Contractor Services for New York City Homeowners
Second Key NYC is a licensed general contractor based in New York City, specializing in the planning, design, permitting, and construction of Accessory Dwelling Units (ADUs). Founded by NYC real estate developers, the company focuses on helping homeowners in Staten Island, Queens, Brooklyn, and the Bronx turn underused property into functional, permitted living spaces.
Their work covers a range of ADU types, including detached backyard ADUs, garage conversion projects, and other configurations permitted under New York City's updated zoning laws. In December 2024, NYC revised its zoning regulations to allow many one- and two-family property owners to build an ADU, opening up new possibilities for eligible homeowners across the boroughs.
How Second Key Approaches the ADU Process
Second Key offers a structured, end-to-end service model designed to reduce the complexity typically associated with construction projects. Their process is broken into several key phases:
- Free Initial Assessment: Homeowners can submit their address for a complimentary ADU feasibility review. This gives property owners a clearer picture of what can be built on their lot based on zoning, lot size, and site conditions.
- Feasibility & Pre-Construction Advisory: A paid feasibility study provides a detailed analysis of buildable options and projected costs. Second Key assembles the project team, coordinates with licensed architects and engineers, and delivers a cost estimate and schedule before construction begins.
- Financing Guidance: The company connects clients with lending partners experienced in ADU construction financing in New York, including HELOCs and construction loans.
- Design, Permitting & Construction: Clients can choose from pre-designed ADU layouts with clear pricing or opt for a custom unit. Second Key manages the full build, including all permitting through the NYC Department of Buildings (DOB), through to the Certificate of Occupancy.
Typical detached ADU projects are priced between $300 and $350 per square foot, depending on size, layout, site conditions, and finishes. Final pricing is confirmed after city plan approval. Most ADU projects are completed within three to six months after permit approval, though permitting and Certificate of Occupancy filings can extend the overall timeline.
In New York City, the maximum allowable ADU size is 800 square feet, limited to one floor unless a garage or parking occupies the ground level. ADU placement and size are also subject to the property's specific zoning district and lot conditions.
Who Second Key Works With
Second Key primarily serves NYC homeowners who are considering an ADU for one of several reasons:
- Generating long-term rental income from a permitted secondary unit
- Housing family members in a separate but connected living space
- Increasing the overall value of their property
The company positions itself as one of the few licensed NYC general contractors focused specifically on ADU construction. Their background in real estate development means they approach each project with an understanding of the full project lifecycle — from zoning analysis to final occupancy.
Second Key's stated mission is to make ADU development accessible to everyday NYC property owners, not just those with significant resources or prior construction experience. They emphasize honest pricing, full transparency, and a streamlined process that removes the burden of coordinating multiple consultants, architects, and subcontractors independently.
All ADU projects require approval from the NYC Department of Buildings, and Second Key handles the entire permitting process on behalf of their clients. Completed ADUs that meet DOB and zoning requirements can generally be used as long-term rentals.