Can you build a duplex in Cohasset, MA?
The current code clearly contemplates dwellings containing two or more dwelling units in the 3A-C district and references multifamily conversion standards in residential districts. But the missing use table prevents a confident by-right conclusion.
Confidence: medium · Last researched August 2026
Dimensional standards in Cohasset, MA
| R-A — minimum lot area | 18,000 square feet — Plus "6,000 square feet" for each additional dwelling unit created in a two-family conversion or a multifamily conversion. |
| R-A — front setback | 20 feet — Except "10 feet" for any portion of a principal building with less than "15 feet" in height. |
| R-A — side setback | 15 feet — Accessory building exception to "3 feet" if less than "15 feet" in height and set back at least "75 feet" from the front lot line. |
| R-A — rear setback | 15 feet — Accessory building exception to "3 feet" if less than "15 feet" in height and set back at least "75 feet" from the front lot line. |
| R-B — minimum lot area | 35,000 square feet — "48,000 square feet" for a two-family conversion; "48,000 square feet for the first two dwelling units in a multifamily conversion plus 8,000 square feet for each additional dwelling unit." |
| R-B — front setback | 30 feet — Except "15 feet" for any portion of a principal building with less than "15 feet" in height. |
| R-B — side setback | 20 feet — Accessory building exception to "6 feet" if less than "15 feet" in height and set back at least "100 feet" from the front lot line. |
| R-B — rear setback | 20 feet — Accessory building exception to "6 feet" if less than "15 feet" in height and set back at least "100 feet" from the front lot line. |
| R-C — minimum lot area | 60,000 square feet — "80,000 square feet" for a two-family conversion; "80,000 square feet for the first two dwelling units in a multifamily conversion plus 10,000 square feet for each additional dwelling unit." |
| R-C — front setback | 30 feet — Except "15 feet" for any portion of a principal building with less than "15 feet" in height. |
| R-C — side setback | 20 feet — Accessory building exception to "6 feet" if less than "15 feet" in height and set back at least "100 feet" from the front lot line. |
| R-C — rear setback | 30 feet — Accessory building exception to "6 feet" if less than "15 feet" in height and set back at least "100 feet" from the front lot line. |
| HAR — front setback | 15 feet |
| HAR — side setback | 10 feet |
| HAR — rear setback | 15 feet |
| VIL — minimum lot area | 5,000 square feet |
| VIL — front setback | 15 feet |
| VIL — side setback | 10 feet — Minimum side yard requirements do not apply where the side lot line abuts a railroad right-of-way. |
| VIL — rear setback | 15 feet |
| 3A-C — minimum lot area | 10,000 square feet — "88,000 square feet for any dwelling containing two dwelling units, plus 4,000 square feet for each additional dwelling unit." |
| 3A-C — front setback | 50 feet — "15 feet" for an accessory freestanding sign; "100 feet" for any dwelling containing two or more dwelling units. |
| 3A-C — side setback | 20 feet — "50 feet" for any dwelling containing two or more dwelling units. |
| 3A-C — rear setback | 20 feet — "50 feet" for any dwelling containing two or more dwelling units. |
| OS — front setback | 30 feet |
| OS — side setback | 20 feet |
| OS — rear setback | 30 feet |
| All districts — lot area calculation rule | May not include any land within the limits of an abutting street or private way, or any portion of the lot below mean high water |
| All districts — front setback measurement rule on narrow rights-of-way | Where a street has a right-of-way width of less than 40 feet, the setback distance shall include an additional 20 feet and be measured from the center line of the street |
Related questions
What are the setback requirements in Cohasset, MA?
Setbacks vary by district. Examples — R-A front setback: 20 feet (conditions apply); R-A side setback: 15 feet (conditions apply); R-A rear setback: 15 feet (conditions apply); R-B front setback: 30 feet (conditions apply). Always confirm the exact yard requirements for your district with Cohasset, MA.
What is the minimum lot size in Cohasset, MA?
Minimum lot size depends on the zoning district — R-A minimum lot area: 18,000 square feet (conditions apply); R-B minimum lot area: 35,000 square feet (conditions apply); R-C minimum lot area: 60,000 square feet (conditions apply); VIL minimum lot area: 5,000 square feet.
How tall can buildings be in Cohasset, MA?
Height limits are set per district — R-A maximum principal height: 35 feet; R-A maximum accessory height: 25 feet (conditions apply); R-B maximum principal height: 35 feet; R-B maximum accessory height: 25 feet.
Full investor analysis
The full Cohasset, MA report breaks down duplex and 2–4 unit feasibility by district, the approval path, and the density/dimensional limits that decide whether the numbers work. First town report is free.
Get the full Cohasset, MA report free →More about Cohasset, MA zoning
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- What are the setback requirements in Cohasset, MA?→
This summary is AI-generated from public municipal sources and is not legal, engineering, or land-use advice. Always verify zoning with Cohasset, MA officials before making decisions.
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