What insulation really costs in Somerville, Cambridge and Greater Boston: 2,089 real jobs on a map
I mapped 2,089 installed insulation jobs across Massachusetts. Here's what a typical job cost in Somerville, Cambridge, Boston and 15 other Greater Boston towns.
Mateus MagnoLicensed Construction Supervisor · October 22, 2026 · 4 min read
Across 2,089 installed insulation jobs I mapped from 2021 to 2026, the typical (median) job in Greater Boston cost about $4,700. Somerville's median was $4,750, Boston's $5,500 and Cambridge's $7,500. Half of all jobs came in under $5,000, but about 1 in 8 went over $20,000. Those were usually whole-house spray foam or new-construction jobs.
"How much does insulation cost?" is one of the most searched home questions in Massachusetts, and most answers online are national averages that don't fit a 1920s two-family in Somerville or a big colonial in Newton. So I went to real numbers.
Over the past few years I built a job map for the insulation crews I work with. It has 4,543 insulation quotes across 221 Massachusetts cities and towns, from 2021 to 2026. 2,089 of them became installed jobs. I removed every name and address. What's left is a clear picture of what insulation actually costs around Somerville, Cambridge and Greater Boston.
The short answer: what a typical insulation job costs
Inside about 15 miles of Somerville there are 1,363 installed jobs on the map. The median job was about $4,700. That means half the jobs cost less and half cost more. Across the whole state the median was about $4,900.
Here's how all 2,089 installed jobs break down by price:
| Job price | Share of jobs | What it usually is |
|---|---|---|
| Under $5,000 | 51% | Attic top-up, a basement rim joist, one or two rooms, a small addition |
| $5,000 – $10,000 | 20% | A full attic with air sealing, a finished attic with knee walls, part of the walls |
| $10,000 – $20,000 | 17% | Spray foam roof lines, a gut renovation, walls plus attic |
| $20,000 and up | 12% | Whole-house spray foam, new construction, multi-unit buildings |
Insulation cost by town in Greater Boston
Here is the median installed job for each town with enough jobs to be meaningful (8 or more):
| Town | Median job | Installed jobs |
|---|---|---|
| Chelsea | $9,500 | 12 |
| Newton | $8,025 | 118 |
| Cambridge | $7,500 | 42 |
| Lexington | $7,300 | 23 |
| Revere | $7,080 | 14 |
| Everett | $6,895 | 8 |
| Malden | $6,600 | 25 |
| Brookline | $5,850 | 17 |
| Arlington | $5,800 | 29 |
| Boston | $5,500 | 176 |
| Watertown | $5,100 | 20 |
| Winchester | $5,100 | 72 |
| Somerville | $4,750 | 52 |
| Medford | $4,000 | 43 |
| Milton | $3,990 | 29 |
| Quincy | $3,895 | 34 |
| Waltham | $3,500 | 29 |
| Belmont | $3,100 | 21 |
Small towns have fewer jobs, so one big project can move their median a lot. Treat Chelsea and Everett as rough. Boston, Newton, Winchester and Somerville have enough jobs to be solid.
Why the same town can show a $2,000 job and a $40,000 job
The median hides a big range. These are the things that move an insulation price the most, in my experience:
- Type of insulation. Blown-in cellulose or fiberglass in an open attic is the cheapest per square foot. Closed-cell spray foam costs the most. In one recent Greater Boston quote, about 1,700 sq ft of closed-cell foam on attic rafters came to roughly $9,600, or about $5.65 per sq ft.
- Where it goes. An open attic floor is easy. Walls behind finished plaster (dense-pack through small holes), sloped ceilings and knee walls take more labor.
- Old insulation removal. Vacuuming out old, dirty or wet insulation adds cost before anything new goes in.
- Air sealing. Sealing the attic floor first is the best money you'll spend, and it's part of the price on good quotes.
- Prep problems. Knob-and-tube wiring, vermiculite or bath fans venting into the attic must be handled first. Read my guide to attic surprises in older homes.
- Size of the building. Newton's higher median mostly reflects bigger single-family homes. Somerville's lower median reflects many smaller jobs on two- and three-family houses.
What this means for your budget
- Somerville and Medford two- and three-families: plan for $3,500–$7,000 for the attic and air sealing. Walls are a separate project.
- Cambridge, Arlington and Brookline: plan for $5,000–$10,000. Many homes here have finished third floors with knee walls and sloped ceilings.
- Newton, Lexington and larger single-family homes: $7,000–$15,000 is common, more with spray foam.
- Gut renovations and additions anywhere in Greater Boston: budget insulation as its own line, usually $8,000–$25,000 depending on size and foam.
Before you pay full price, check Mass Save insulation rebates for 2026. Most homeowners can get 75% off approved insulation, and income-eligible households can get it at no cost.
How I built this map (and its limits)
The map plots real insulation quotes from 2021 to 2026. It shows the town, the year, the price and whether the job went ahead. I removed every name and street address. Keep in mind:
- It is one set of crews' jobs, not the whole Massachusetts market.
- The prices include both homeowner and builder jobs, and every type of insulation.
- 2026 covers only part of the year.
Even so, 2,089 installed jobs is a lot more real-world data than a national average. For the region-by-region view, read my Massachusetts insulation map by region. For my home turf, read insulation in Somerville and Cambridge's older homes.
Get a real number for your house
I'm Mateus, a licensed builder based in Somerville. Magno & Co installs and upgrades insulation (blown-in, fiberglass and spray foam) in Somerville, Cambridge and across Greater Boston. Book a free walkthrough and you'll get a clear written price with the R-value, square footage and air sealing spelled out.
Frequently asked questions
How much does insulation cost in Greater Boston?
Across 1,363 installed jobs within about 15 miles of Somerville from 2021 to 2026, the median insulation job cost about $4,700. Half of all jobs were under $5,000, while whole-house spray foam and new-construction jobs often ran over $20,000.
How much does insulation cost in Somerville, MA?
The median installed insulation job in Somerville was $4,750 across 52 jobs on my map. Many are attic and air-sealing jobs on two- and three-family homes.
Why is insulation more expensive in Cambridge than Somerville?
The Cambridge median was $7,500, compared with $4,750 in Somerville. Cambridge homes more often have finished third floors with knee walls and sloped ceilings, plus more gut renovations, which take more labor and spray foam.
Is spray foam more expensive than blown-in insulation?
Yes. Blown-in cellulose or fiberglass in an open attic is usually the lowest cost per square foot. Closed-cell spray foam costs the most. One recent Greater Boston quote for about 1,700 sq ft of closed-cell foam on attic rafters was about $9,600.
Mateus Magno is the founder of Magno & Co — a licensed Massachusetts Construction Supervisor (CS-123658), registered Home Improvement Contractor (HIC #220484) and certified Lead-Safe Renovator Supervisor who has renovated and managed over $3 million in projects across Greater Boston.
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