Across 493 permits filed since 2025-01-25, the median is $88,805; half of projects fall between $25,000 and $324,000. Figures are permit valuations reported to building departments. National cost guides answer this question with averages from other markets; these numbers are what homeowners in Kings County (Brooklyn), NY actually reported when they pulled permits.
Recent filings
- CONVERT EX BUILDING FROM 2 TO 1 FAMILY. RENOVATE & ENLARGE EXISTING BUILDING. CONSTRUCT NEW REAR ADDITION 1 STORY + BASEMENT. CONSTRUCT NEW VERTICAL PENTHOUSE ADDITION. CONSTRUCT NEW WALLS, FINISHES, CABINETRY PER PLANS. OBTAIN NEW CO FOR 1Brooklyn · 2026-07-24$1,279,725
- Herewith filing extension of existing sanitary, vent and water piping to new and relocated plumbing fixtures, as per plans. Filed in conjunction with ALT CO B01304729.Brooklyn · 2026-07-21$46,018
- Foundation work for a new one-story extension in the rear of the building. for a 2-family dwelling.Brooklyn · 2026-07-21$20,000
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 home addition permits in Kings County (Brooklyn), NY came in between $25,000 and $324,000. 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
Home addition in New YorkHome addition in ConnecticutHome addition on Long Island