After nearly a year of discussions, the Chilmark planning board will hold the first public hearing Monday night on a proposed bylaw to regulate house size.

The draft bylaw calls for two thresholds of regulation. Residential building projects between 3,500 and 5,500 square feet per first acre would require special permits from the zoning board of appeals. Total construction would be capped at 5,500 square feet per first acre.

The planning board is also proposing adding new language to the zoning definitions section of the existing bylaw to include detached bedrooms.

The bylaw and definition are slated for a vote at the annual town meeting in April. The public hearing seeking input and potential revisions to the draft bylaw begins at 4:30 p.m. at the Chilmark town hall.

“[The bylaw] seeks to ensure that future residential development does not overwhelm Chilmark’s rural atmosphere; detract form its geographical diversity — its seashore, ponds, stonewall boundaries, open agricultural space — or the vistas from its roadsides; is built in scale with past development practices with regard to bulk and building coverage; and preserves the existing and historic rural development pattern and character of the town set forth in the town master plan,” the draft says. The planning board has met weekly since last January to develop the bylaw.

The new language comes in the wake of several large building projects in Chilmark that have sparked debate on the merits of regulating house size at town regulatory boards. The Martha’s Vineyard commission has also taken up the thorny issue, but last week decided not to include large houses in its development of regional impact (DRI) checklist.

The new Chilmark bylaw would limit the “residential built area” of a home, which is measured by any finished space other than the basement and includes the main dwelling, detached bedrooms, garage or any other accessory structures. Residential built area is calculated using the same number town assessors record as livable floor space.

Should the bylaw be approved at town meeting in the spring,all new construction under 3,500 square feet per one acre of residential built area would be regulated according to existing bylaws.

A special permit would be required from the zoning board of appeals for construction between 3,500 square feet and 5,500 square feet per one acre. Applicants would be permitted an additional 250 square feet for each additional acre.

No building permits would be issued for construction larger than 5,500 square feet for the first acre plus 250 square feet for each additional acre. For example, three acres of land would be limited at 6,000 square feet of total construction.

Chilmark has minimum three-acre zoning.

If an existing residential built area exceeds the threshold, a homeowner would be allowed a one-time-only exception to increase the existing residential built area threshold by 5 per cent.

The planning board is also proposing a definition for a detached bedroom in an effort to differentiate the term from guest houses and accessory structures. No definition exists in the current zoning bylaw and confusion between the three terms became an issue during a large building project on Nashaquitsa Pond. The new definition would limit the size of a detached bedroom to 400 square feet, similar to existing bylaws in the towns of Edgartown and Oak Bluffs. The bedroom may contain a bathroom but no stove or refrigerator. No acreage requirement is needed for a detached bedroom.

A special permit from the zoning board would be needed to build more than one detached bedroom.

The proposed bylaw would also establish a list of checks and balances for the zoning board to consider during the permitting process. Items include the impact of the project on the existing rural character, retaining natural buffer areas and natural features of the site, landscaping, contours of the land, lighting and maintaining the visual integrity of ridge lines.