Updated November 2026
Most Winchester houses were built before 1970, and an addition there usually ties into a lot of existing house. Here is what our additions cost and what moves the number.
Short answer: A home addition in Winchester, MA runs about $100,000 to $140,000 for a single room of about 250 square feet. With a bathroom, homeowners paid $205,000 to $360,000 on 18 additions we built from 2020 to 2025; with a kitchen and bathroom, $355,000 to $545,000 on 24.
| Single-room addition, about 250 sq ft (estimated from our cost per sq ft) | about $100k–$140k |
| Addition with a bathroom | $205k–$360k |
| Addition with a kitchen and bathroom | $355k–$545k |
| Per square foot added (150 sq ft and up, foundation included) | $345–$555 |
From what homeowners paid on PEGASUS projects built 2020–2025, across all the towns we work in. See every range and get one for your house →
We have built 24 projects in Winchester, 7 of them additions or second stories. That is too few to publish a Winchester-only price range honestly, so the numbers above come from all our additions from 2020 to 2025. Our prices change with the scope of the work, not the town.
About 70% of Winchester homes were built before 1970. Tying new space into an older house is where much of the cost goes: matching floor levels, carrying old walls on new beams, and bringing systems up to date.
On our additions with a bathroom, the cost splits roughly like this: carpentry, windows and doors 42%; walls, floors, tile and paint 18%; electrical 12%; plumbing and heating 10%; demolition and site prep 8%; permits and project management 7%; cabinets and counters 3%.
People are often surprised that the shell, not the finishes, is most of what an addition costs. Foundation, framing, roof, siding and windows come first, and that is where most of the money goes.
— Geoff Shafer, owner
Design takes about 4–6 weeks. Construction on an addition with a bath runs about 16–20 weeks; with a kitchen and bath, about 18–29 weeks. Design is its own agreement: 1.5% of the construction estimate, with a $1,000 retainer to start.
More on Winchester's demolition review, ADUs and our work in town: home remodeling in Winchester.
About $100,000 to $140,000 for a single room of about 250 square feet. Additions with a bathroom ran $205,000 to $360,000 on our projects, and with a kitchen and bathroom $355,000 to $545,000.
Not for the same work. Our prices follow the scope, not the town. An older house can mean more tie-in work, which shows up as scope.
Second-story additions we built from 2020 to 2025 ran about $215,000 to $394,000. See our second-story additions page.
Only if you change the job or choose finishes above your allowances. Your agreement is a fixed price with allowances for the finishes you choose.
Get a cost range, or tell us about your house. See our home additions page for more.
Geoff Shafer has run PEGASUS Design-To-Build in Melrose for 25 years. He is a Massachusetts licensed Construction Supervisor and registered Home Improvement Contractor (HIC 137663).