Across 118 permits filed since 2025-03-11, the median is $40,000; half of projects fall between $19,250 and $99,602. 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 BASEMENT IN ACCORDANCE WITH NYS AND RVC CODERockville Centre · 2026-09-04$60,000
- The reconstruction of an existing dwelling to a 42.6 x 38.1 (oa) (3,173 sf) two story one (1) family dwelling of type VB construction over existing and proposed poured concrete foundation systems with unfinished basements, a 10.5 x 4.67 pouVillage of Mineola · 2026-08-27$447,734
- NEW BEAM AND RENOVATIONS TO EXISTING FINISHED BASEMENT BUILT IN ACCORDANCE WITH NYS AND RVC CODE.Rockville Centre · 2026-08-20$28,500
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 $19,250 and $99,602. We exclude permits under $1,000, jobs filed as whole-house construction, and counties whose building departments don't reliably report valuations.