Somerville, MA Building Setbacks & Zoning: Lot Coverage Limits (2026)
Key Facts
- Governing section
- Zoning Ordinance §2.4.2.c.i, Lot Coverage
- Cottage (NR district)
- 60% max lot coverage, §3.1.7
- Semi-Detached Triple Decker (UR)
- 65% max, §3.2.7
- General Building (Mid-Rise 3)
- 90% max, §4.1.8
- Coverage measured
- At ground-story exterior wall footprint
- Porous pavement
- Counted via manufacturer's runoff coefficient
- Waiver authority
- Building Official, egress retrofits only, §2.4.1.b
Summary
Somerville's Zoning Ordinance caps lot coverage, the share of a lot covered by buildings, structures and impervious surface, on a per-building-type basis under §2.4.2.c.i. A Cottage in the Neighborhood Residential district tops out at 60%, a Semi-Detached Triple Decker in Urban Residential at 65%, and mid-rise types like the General Building can reach 90%, so the cap depends entirely on district and building type chosen.
i. Lot Coverage a). The maximum area of a lot that is permitted to be covered by the combination of principal buildings, accessory buildings, accessory structures and impermeable surfaces. b). The lot coverage of a structure is measured from the outside of the exterior walls at the ground story, including covered porches and other building components. c). The lot coverage (and permeable area) of porous asphalt, pervious concrete, paving stones, or grass pavers is calculated using the runoff coefficient provided by the manufacturer.
Full Breakdown
Section 2.4.2.c.i defines Lot Coverage as 'the maximum area of a lot that is permitted to be covered by the combination of principal buildings, accessory buildings, accessory structures and impermeable surfaces.' Coverage is measured 'from the outside of the exterior walls at the ground story, including covered porches and other building components,' and porous asphalt, pervious concrete, paving stones or grass pavers still count toward coverage, but only using the manufacturer's runoff coefficient rather than as fully impervious ground.
The percentage cap is not one citywide number; it's set per building type in each district's dimensional table. The Cottage building type in the Neighborhood Residential (NR) district, §3.1.7, caps Lot Coverage at 60%. The Semi-Detached Triple Decker in the Urban Residential (UR) district, §3.2.7, allows up to 65%. Mid-rise building types push the cap much higher: the General Building type at §4.1.8, used in the Mid-Rise 3 Story (MR3) district, allows up to 90% lot coverage, reflecting Somerville's denser urban core.
Somerville also allows a narrow waiver: under §2.4.1.b, the Building Official may waive the §2.4.2.c.i Lot Coverage standard, along with Building Placement, Massing & Height and Building Components rules, when a project is constructing or modifying an accessible means of egress for an existing building, but only if no other code-compliant design solution is feasible without undue financial hardship; the waiver decision must be documented in the public record under §2.4.1.d.
Violations & Fines
Exceeding the Lot Coverage cap for a given building type is a zoning violation the Building Official can catch at building permit review or through a site inspection, since coverage is verified against the exterior wall footprint at the ground story. A project that comes in over the district's percentage, say above 60% for a Cottage in NR or 65% for a Triple Decker in UR, cannot obtain a building permit or certificate of occupancy without first reducing impervious area or securing the narrow egress-related waiver under §2.4.1.b, which the Building Official must document in the public record.
Frequently Asked Questions
What counts toward lot coverage in Somerville?
What is the maximum lot coverage for a house in Somerville?
Can Somerville waive the lot coverage limit?
Why is lot coverage so much higher in Mid-Rise districts?
Sources & Official References
Other rules in Somerville
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Lot Coverage Limits in Nearby Cities
How other cities in this county handle lot coverage limits.