Across 56 permits filed since 2025-01-25, the median is $35,000; half of projects fall between $7,875 and $76,250. Figures are permit valuations reported to building departments. National cost guides answer this question with averages from other markets; these numbers are what homeowners on Long Island actually reported when they pulled permits.
Recent filings
- FINISHED BASEMENTRockville Centre · 2026-07-23$40,000
- Construct 60 SF front porch addition Interior alterations 1st floor, convert attic to habitable space, finished basement.Village of Garden City · 2026-07-22$115,000
- CONSTRUCT 2ND STORY ADDITION (150 SQ. FT.) WITH COVERED BALCONY. UNDERPIN EXISTING BASEMENT AND FIINISH GOLF SIMULATOR ROOM. INTERIOR ALTERATIONS TO 1ST FLOOR BUILT IN ACCORDANCE WITH NYS AND RVC CODE. VFR TRUSS PLACARD REQUIRED FOR C/O. Rockville Centre · 2026-07-06$225,000
How to read these numbers
Permit valuations are the project cost the applicant reports to the building department. They skew slightly low — nobody rounds up for the permit fee — and scope varies, so the middle-half range is the honest picture: half of all basement finishing permits on Long Island came in between $7,875 and $76,250. We exclude permits under $1,000, jobs filed as whole-house construction, and counties whose building departments don't reliably report valuations.
Same project, other places
Basement finishing in New YorkBasement finishing in Connecticut