Alec's Construction

ADU Construction on Long Island by Alec's Construction

Accessory dwelling units are among the fastest-growing construction trends on Long Island. Whether referred to as ADUs, in-law suites, granny flats, or backyard cottages, these secondary living spaces give homeowners a practical way to house aging parents, generate rental income, or add value to their property. Alec's Construction, a licensed and insured general contractor based in East Patchogue, handles ADU projects across Suffolk County, including communities in Brookhaven, Islip, and surrounding towns.

New York State's evolving regulations have made ADU construction more accessible than before, and Suffolk County homeowners are increasingly exploring their options. Alec's Construction manages every phase of the process, from initial feasibility assessment through final inspection and certificate of occupancy.

What is an ADU?

An accessory dwelling unit is a self-contained residential unit located on the same lot as an existing single-family home. It has its own entrance, kitchen, bathroom, and sleeping area, functioning as a fully independent living space while sharing the property with the primary home.

The right type of ADU depends on the property, budget, and goals of the homeowner. Alec's Construction works with clients across several ADU formats:

1. Garage conversion: Converting an attached or detached garage into a living space is often the most cost-effective route. The existing structure means work is focused on insulation, drywall, plumbing, electrical, and finishes. Many Long Island homes have oversized two-car garages that convert into comfortable 400 to 600 square foot units.
2. Basement conversion: Full basements are common in Suffolk County homes and often have adequate ceiling height for habitable space. This type of ADU requires egress windows, waterproofing, a separate entrance, and code-compliant mechanical systems.
3. Above-garage apartment: Where structural capacity allows, building upward above a detached garage adds living space without sacrificing parking — a practical option on properties with garages set back from the street.
4. Detached new construction: A standalone ADU built in the backyard offers the most privacy and design flexibility, typically ranging from 400 to 1,000 square feet. These require a new foundation, full utility connections, and must meet setback and lot coverage requirements.
5. Interior conversion: Carving out a portion of an existing home — such as an unused wing or a large bonus room — creates an ADU with shared walls but independent access and amenities.

Permits, Regulations, and Costs

ADU regulations in Suffolk County are enforced at the town level. Each town — whether Brookhaven, Islip, Babylon, or Smithtown — has its own zoning code. Some permit ADUs by right in certain zones, while others require a special use permit or variance. Brookhaven Town, which covers much of Alec's Construction's service area, has provisions for accessory apartments, though requirements around owner-occupancy, lot size, and parking can vary by zoning district.

If the property relies on a septic system, Suffolk County Health Department approval is also required to confirm the existing system has adequate capacity, or that an upgraded system will be installed. Navigating these requirements is one of the key reasons to work with a contractor familiar with local building departments.

Building an ADU on Long Island typically requires the following permits and approvals:

1. Building permit from the town's building department, including architectural plans
2. Suffolk County Health Department approval for septic capacity (where applicable)
3. Electrical permit for new or modified electrical service
4. Plumbing permit for bathroom and kitchen connections
5. Fire safety compliance including smoke detectors, carbon monoxide detectors, and egress requirements

Alec's Construction handles the entire permit process for ADU clients — preparing plans, submitting applications, scheduling inspections, and ensuring everything passes without the homeowner needing to visit the building department.

Cost ranges for ADU construction in Suffolk County in 2026 are as follows:

1. Garage conversion: $50,000 to $100,000
2. Basement conversion: $60,000 to $120,000
3. Above-garage apartment: $80,000 to $150,000
4. Detached new construction: $150,000 to $300,000+

These ranges include design, permits, construction, and finishes. Complex site conditions, high-end finishes, or septic system upgrades can push costs toward the upper end. Alec's Construction provides detailed, transparent written estimates before any work begins.

Project Timelines and Return on Investment

From initial consultation to move-in, a typical ADU project follows this general timeline:

1. Design and planning: 2 to 4 weeks
2. Permitting: 4 to 8 weeks, depending on the town
3. Garage or basement conversion construction: 6 to 10 weeks
4. Detached new construction: 12 to 20 weeks

Total project duration from first meeting to completion typically ranges from 3 to 7 months, depending on scope and permitting speed. Seasonal backlogs at local building departments can occasionally add a few weeks.

From a financial standpoint, a one-bedroom ADU in Suffolk County can generate $1,500 to $2,500 per month in rental income, depending on location and finish level. Homes with legal, permitted ADUs also tend to appraise higher than comparable properties without them. Beyond financial return, ADUs offer practical flexibility — housing an aging parent, providing space for an adult child, or creating a dedicated home office or studio.

Alec's Construction is a Latinx-owned business and offers military discounts. They serve over 36 communities across Suffolk County, from East Patchogue to the Hamptons and the North Shore.