Weston & Sampson tells Nantucket commission island could add thousands of homes under current rules

Consultants from Weston & Sampson told the Nantucket Economic Development Commission on June 23 that, under current zoning and environmental constraints, the island could accommodate thousands of additional dwelling units — with a wide range depending on assumptions about demand and build‑out rules.

The firm presented a parcel‑by‑parcel GIS build‑out update completed in March 2025. “The purpose of this report was to provide technical information … to inform your policy decision‑making and future planning efforts,” said Joanna Nato, senior planner with Weston & Sampson. Dan Sheehan, senior associate project manager, described the firm’s prior work on the 2020 sewer master plan and said this update covers the town’s remaining unassessed parcels.

The report distinguishes maximum theoretical capacity from likely development. Weston & Sampson estimated a very large theoretical maximum if every developable parcel were built to zoning limits: roughly 11,000 additional dwelling units on the parcels outside the earlier sewer master plan, and a combined island maximum that the consultants summarized as about 17,000 dwelling units when existing units are added to future capacity. Using recent development rates (about 209 units per year over the last five years), the consultants said a more plausible growth through 2050 would be about 5,000–6,000 new dwelling units. Under low population growth assumptions, the 2050 demand projection could be as small as roughly 800 units.

Commissioners pressed for clarity about what was included. Commissioner Hillary asked whether the sewer master plan areas were excluded; Sheehan confirmed those needs areas were excluded from the parcel inventory shown in this update because they were analyzed separately in 2020. Chair David Iverson and other commissioners asked the consultants to add a short section that consolidates the 2020 sewer master plan numbers with the 2025 update; Joanna Nato agreed to include that summary in the final report.

Public commenters raised neighborhood‑level concerns. Bruce Mandel of the Madaket Conservation Association said Madaket’s own assessments show a much larger bedroom‑count exposure if Title 5 constraints were removed; he cited a community estimate that Madaket could see thousands of additional bedrooms if septic limits changed. Sheehan and Nato said the Weston & Sampson analysis counts dwelling units, not bedrooms, and that bedroom counts change plumbing and infrastructure needs differently than dwelling unit totals.

The consultants described major data choices and constraints: parcels counted were updated as of March 2025; they excluded parcels already analyzed in the 2020 sewer master plan; they removed parcels constrained by state, federal or local land protections and environmental GIS layers (MassGIS). Sea level rise scenarios reduced developable area slightly but did not change the report’s overall findings in a material way, the presenters said.

Commissioners and commenters suggested additional analytical layers: mapping year‑round tax‑exempt lots to help identify likely year‑round versus seasonal demand, flagging lots created under Chapter 41, Section 81L (preexisting structure subdivision) that the town has historically treated as buildable, and noting where large private holdings are unlikely to be subdivided. Several speakers emphasized that the maximum theoretical numbers are illustrative and depend on private owner decisions, conservation purchases, zoning changes and infrastructure investments.

The commission did not take formal action on the report at the June 23 meeting. Commissioners asked staff and Weston & Sampson to add a consolidated table that includes the earlier sewer master plan figures and to produce parcel maps and zoomable PDFs for final review before the commission considers adoption.