An addition is new living space, built up, out, or inside a part of the house nobody lives in yet. The Long Island builders quoted on this page cover four kinds: a dormer on a cape, a second story on a ranch, a ground-level addition off the back, and a garage turned into a room.
Which addition fits your house
Absolute Builders in West Babylon matches the job to the house style:
- Cape Cod. The easiest house to dormer. A shed dormer across the back is the usual choice.
- Ranch. Going up turns it into a two-story house. The hard part is the staircase, which takes space from a first-floor room.
- Split-level. The most complicated, with staggered floors, structural steel and several roof levels.
Benitez Remodeling adds two limits. A dormer needs framed space on the second floor to start from, so a one-story house without an attic floor cannot have one. And roof trusses can rule a dormer out without major structural work. A full second story needs an engineer to confirm the foundation and first floor can carry it.
Published addition prices
| Job | Price | Who says |
|---|---|---|
| Small gable dormer | $18,000 to $30,000 | Absolute Builders (2026) |
| Full shed dormer | $35,000 to $75,000 | Absolute Builders (2026) |
| Dormer with a bathroom | $45,000 to $100,000 | Absolute Builders (2026) |
| Dormer, per square foot of new space | $300 to $450 | Benitez Remodeling (Jul 2026) |
| Full second story, per square foot | $235 to $360 | Kuhn Construction (Sep 2026) |
| Full second story, per square foot | $275 to $375 | Benitez Remodeling (Jul 2026) |
| Full second story on a 1,100 to 1,600 sq ft ranch | $285,000 to $575,000 | Kuhn Construction (Sep 2026) |
| Partial second story, 50 to 70 percent of the footprint | $215,000 to $385,000 | Kuhn Construction (Sep 2026) |
Absolute Builders also lists a full second story with dormers at $90,000 to $150,000 and up, far below Kuhn’s figure for a ranch. The two are probably not pricing the same scope, which is the reason to ask any builder exactly what their number covers: plans, engineering, stairs, heat, a bathroom, finished walls and floors.
Absolute Builders says a bathroom adds $15,000 to $30,000 to a two-bedroom dormer, skylights run $1,500 to $3,500 each, and a ductless mini-split for the new rooms is about $4,000 to $6,000. Kuhn Construction tells clients to hold 10 to 15 percent in reserve.
Turning the garage into a room
Benitez Remodeling’s July 2026 prices:
| Garage job | Price |
|---|---|
| One-car garage, no plumbing | $18,000 to $30,000 |
| Two-car garage to a bedroom or in-law suite with a bathroom | $35,000 to $60,000 and up |
| Framing in the door opening and matching the siding | $3,000 to $7,000 |
| Ductless mini-split for heat and air | $4,000 to $7,000 |
| Insulation and drywall | $4,000 to $7,000 |
Benitez says garages usually are not tied into the house’s ductwork, which is why the mini-split is the usual heat. It also warns that some Nassau villages tie off-street parking minimums to the number of bedrooms, and that losing a covered parking spot can hurt resale on a small lot.
Permits, zoning and the county health department
The Town of Huntington lists additions among the projects that need a building permit, and the Town of Islip counts enlarging a house in any direction. Kuhn Construction describes the sequence in Islip: plans, the permit, inspections at stages, then the town’s sign-off and certificate. The town zoning code sets the setbacks, lot coverage and height limits that decide how big you can go.
Two Long Island extras can change the plan:
- Flood zones. Kuhn Construction says waterfront and flood-zone homes may fall under FEMA’s 50 percent rule on larger projects.
- Septic areas in Suffolk. Benitez Remodeling says an addition that adds a bedroom can trigger a Suffolk County Health Department review, while a dormer that adds no bedroom usually avoids it.
Absolute Builders puts permit approval at 4 to 12 weeks, the biggest variable in the schedule.
Before you hire an addition builder
- Who draws the plans and does the engineering, and is that in the price?
- Is a survey needed, and who orders it?
- Does the number include stairs, heat, a bathroom and finished interiors?
- Will we need to move out, and for how long?
- What is your county home improvement license number?