Across 37 permits filed since 2025-04-29, the median is $15,000; half of projects fall between $4,000 and $88,800. 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 Middlesex County, CT actually reported when they pulled permits.
Recent filings
- *Rough and finish wire 2 story addition on existing home. Including, bathroom, bedroom, and living area.Town of Westbrook · 2026-10-20$4,000
- *618 SF music studio addition to Oxford Academy Knight Hall. This project approved based on drawings received 10/20/2026Town of Westbrook · 2026-10-20$223,000
- Construction of 22' x 22' addition to garage with 2nd floor addtion on existing garage 20' x 30'Haddam · 2026-08-27$88,800
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 Middlesex County, CT came in between $4,000 and $88,800. We exclude permits under $1,000, jobs filed as whole-house construction, and counties whose building departments don't reliably report valuations.
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