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Weymouth, MA Accessory Structures: ADU Rules (2026)

Few Restrictions

Compiled from the official code textEditor Martyn O'NeillLast verified September 2026

ADU rules in Weymouth, MA, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.

Key Facts

Code Section: Weymouth Code Ch. 120, Art. 29 (Measure 24-119)
Max Size (small lots): 750 sq ft (lots under 25,000 sq ft)
Max Size (large lots): 900 sq ft (lots over 25,000 sq ft)
Ineligible Lots: Under 5,000 sq ft
Parking: 1 space (waived within 0.5 mi of transit)

ADU Eligibility Quick-Check

An Accessory Dwelling Unit (ADU) is a smaller, independent living unit on the same lot as a single-family home: converted garages, detached cottages, basement or attic conversions, and attached additions all qualify. Most states have streamlined ADU permitting since 2020, but local rules still control size, height, and setback.

Is your lot zoned single-family or multi-family residential?
Does your lot have at least 1,200 sq ft of buildable space?
Is your existing home owner-occupied (in most states this is not required, but some require it for ADU permits)?
Will the ADU stay under your state's size cap (commonly 850-1,200 sq ft for detached)?
Can you provide one off-street parking space (waived in many states within 0.5 mi of transit)?

If you answered 'yes' to most of these, you likely qualify in Massachusetts under recent ADU streamlining laws. The Weymouth, MA rules below cover local size, height, and setback requirements.

Summary

Weymouth Town Council passed ADU Ordinance Amendment (Measure 24-119) adding Article 29 to Chapter 120. ADUs are allowed by right on single-family lots up to 900 sq ft or 50% GFA. Lots under 5,000 sq ft are ineligible.

Section 3. No zoning ordinance or by-law shall regulate or restrict the use of materials, or methods of construction of structures regulated by the state building code, nor shall any such ordinance or by-law prohibit, unreasonably regulate, or require a special permit for the use of land for the primary purpose of commercial agriculture, aquaculture, silviculture, horticulture, floriculture or viticulture, nor prohibit, unreasonably regulate or require a special permit for the use, expansion, reconstruction or construction of structures thereon for the primary purpose of commercial agriculture

Source: Town of Weymouth BylawsView official code

Full Breakdown

Under Weymouth Code Chapter 120, Article 29 (effective 2025 per Measure 24-119), ADUs are permitted by right on single-family lots. Size limits: 900 sq ft or ½ the GFA of the principal dwelling, whichever is smaller. For lots over 25,000 sq ft, detached ADUs may reach 900 sq ft. For lots under 25,000 sq ft, detached ADUs are limited to 750 sq ft. Lots under 5,000 sq ft are ineligible. ADUs may not exceed 2 stories or 25 feet, and may not exceed the height of the primary structure. Side setbacks are 10 feet (18 feet on corner lots); rear setback is 20 feet or ⅕ lot depth. One off-street parking space required (waived within 0.5 miles of transit). All ADUs require a building permit, design review, and Site Plan Approval.

Violations & Fines

Non-compliant ADUs subject to zoning enforcement.

Frequently Asked Questions

Can I build an ADU on my property in Weymouth?

What are the size limits for an accessory dwelling unit in Weymouth?

Code Section: Weymouth Code Ch. 120, Art. 29 (Measure 24-119). Max Size (small lots): 750 sq ft (lots under 25,000 sq ft). Max Size (large lots): 900 sq ft (lots over 25,000 sq ft). Ineligible Lots: Under 5,000 sq ft.

Sources & Official References

[1]Town of Weymouth Bylaws

Other rules in Weymouth

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All Weymouth rules

How Weymouth compares: Easiest Cities to Build an ADU·Compare Weymouth to another location·View the Massachusetts accessory structures overview

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