LI Basement Pro in North Massapequa says the high water table here makes water getting in common, and calls finishing a wet basement without fixing it one of the costliest mistakes a homeowner can make.
Deal with the water first
LI Basement Pro prices waterproofing before finishing at $3,000 to $12,000 and tells homeowners never to skip it. If the walls sweat, the corners stain after a storm or the carpet from the last owner smelled, get that looked at before anyone quotes drywall.
Basement finishing prices by level
LI Basement Pro, March 2026. Its totals include $500 to $1,500 in permit fees.
| Level | Per square foot | Includes | 650 sq ft basement |
|---|---|---|---|
| Basic | $50 to $65 | Vinyl plank floor, drop ceiling, basic recessed lights, no bathroom | $32,500 to $42,250 |
| Standard | $65 to $75 | Drywall ceiling, better lighting, half-bath rough-in | $42,250 to $48,750 |
| Premium | $75 to $85 and up | Full bathroom, custom ceiling, upgraded flooring, built-ins | $48,750 to $55,250 and up |
A bathroom changes the number most. LI Basement Pro adds $6,000 to $12,000 for a half bath and $10,000 to $18,000 for a full one, more when the drain runs far or needs an ejector pump to lift waste up to the sewer or cesspool line.
Ceiling height, beams and drop ceilings
Ceiling height is where many Long Island basements run out of room. The Village of Floral Park’s guidelines, written to the 2025 New York State Residential Code, set the minimums:
- 6 feet 8 inches in an existing basement
- 6 feet 4 inches in a bathroom or laundry
- 7 feet in new construction
LI Basement Pro says Levitt-era capes often have 6 feet 4 inches to 7 feet down there, which leaves some of them under the 6 foot 8 inch minimum before a ceiling even goes in. A drop ceiling, the suspended grid with lift-out panels, is in its basic tier and keeps pipes and valves reachable. A drywall ceiling is in the standard tier. For low spots it wraps beams and uses low-profile drop ceiling systems.
Egress windows and alarms
Floral Park’s guidelines spell out the escape opening a basement needs where one is required:
- at least 5.7 square feet of clear opening, at least 24 inches high and 20 inches wide
- a sill no more than 44 inches above the floor
- a window well of at least 9 square feet when the sill is below grade, with a fixed ladder or steps if it is deeper than 44 inches
The same guidelines call for hard-wired, interconnected smoke alarms and carbon monoxide alarms with backup power. LI Basement Pro prices an egress window at $3,500 to $8,000 each with the digging, structural work and well, and says one is required for any basement bedroom.
Basement permits
Huntington puts finished basements on its building permit list. Islip wants an interior alteration permit for turning a basement into living space, and the same permit for digging out a crawl space or adding an outside basement entrance. Floral Park adds a plumbing permit, a backwater valve on all basement plumbing, insulation to the state energy code, and drawings stamped by a New York licensed architect or engineer.
Floral Park also bans bedrooms and second kitchens in basements. News12 reported that whether a basement apartment can ever be legal depends on the town, and several Long Island towns do not allow new ones. Check with your building department before you plan to rent the space or put anyone to sleep down there.
What to ask a basement contractor
- Did you check for moisture, and what do you propose to fix it?
- What ceiling height will I end up with, and is it legal for the room I want?
- Drop ceiling or drywall, and how do I reach the valves later?
- Does a bathroom need an ejector pump in my house?
- Who draws the plans and files the permit?