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Home additions in Lexington, MA

Lexington additions are sized by the gross floor area cap, and homes built before 2024 get the larger table, which often favors adding on over a rebuild.

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The first thing we do for an addition in Lexington is calculate the lot's maximum gross floor area under the older-home table and subtract what the house already has, garage and porches included. That remainder is the real budget for new space, and it is usually larger than the same lot would allow for a new house under the 2024 table.

After that come the setbacks on the town's residential sheet, the half-story and dormer limits for any second-floor work, and the tree bylaw if the addition grows the footprint enough to count as major construction. Additions over 1,000 square feet fall under the fossil-fuel-free bylaw, so heating for the new space goes electric. In Turning Mill or Pierce-Lockwood the neighborhood commission reviews the design, and on Mass Ave the Historic Districts Commission does.

Lexington rules that apply

1
Residential gross floor area cap
The total gross floor area of all buildings on a one- or two-family lot can't exceed a limit set by lot area. New homes use one table and homes built before January 1, 2024 use a more generous one, and the count includes garages, porches, half stories and basements with 6'8" ceilings.
Source: Lexington Building Dept.: Zoning By-Laws to Consider for Residential Construction (PDF)
2
Neighborhood Conservation District review
Turning Mill and Pierce-Lockwood were made Neighborhood Conservation Districts at the 2018 Town Meeting, and each has its own commission and bylaw. House alterations there go to that commission for approval.
Source: Town of Lexington: Current Neighborhood Conservation Districts
3
Tree bylaw on major construction
On lots undergoing demolition or major construction, trees 6 inches DBH or larger in the front (30 ft) and side and rear (15 ft) setbacks are protected. Removing them requires a Tree Removal and Mitigation Permit and replanting or a per-inch payment, and kept trees need a certified arborist's protection plan before any site work.
Source: Lexington Tree Committee: Tree Bylaw Rules & Regulations Quick Start Guide
4
Fossil-fuel-free bylaw
Since March 21, 2024, Lexington issues no building permits for new construction or major renovation that installs new on-site fossil fuel infrastructure. Major renovation covers gut jobs over 50% of the home and residential additions over 1,000 square feet, with waivers possible from the Building Commissioner.
Source: Town of Lexington: Fossil Fuel Free Demonstration Program

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Questions

Home additions in Lexington, answered.

Is it better to add on or rebuild in Lexington?

Often adding on, because houses built before January 1, 2024 use a more generous gross floor area table than new homes. We calculate both before you decide.

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Home additions near Lexington.

Where this information comes from

Rules change. These are summaries of Lexington's and Massachusetts' published rules as of our last check, not legal advice; your project's permits are confirmed with the town when we file them.

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Planning home additions in Lexington?

We'll come out, measure, listen, and send a written estimate. The visit is free and there's no pressure to sign.

Call 617-934-1875