Key Takeaways
•The short answer: According to Boston.gov, the city's inclusionary rules require projects of seven or more units to set aside 17-20 percent of homes at below-market prices. In this hypothetical example, using the Globe's figures and assuming a seventh unit costs about as much to build as a market unit, it earns $810 a month less. A small developer may stop at six.
•The 7-to-9 "dead zone": Projects just over the trigger carry the set-aside without enough units to spread the cost. In this example, the numbers favor six units or a much larger building.
•No cut to the percentage yet: The Boston Globe (Sept. 24, 2026) reports Boston, Cambridge, and Somerville "aren't budging" on their requirements. Separately, the Boston Planning Department's board approved agreements on Oct. 15, 2026 enabling tax abatements for four large projects totaling about 1,400 homes.
•What this means for a lot: In this example, a builder who stops at six units would value a lot on what six units earn, not on the largest building zoning allows.
Why Is Unit Seven a Bad Deal?
Own a small lot in Dorchester, Roslindale, Hyde Park, Jamaica Plain, or East Boston? This question matters to you directly. More units should mean more value. In Boston, that math breaks down at unit seven.
Boston.gov (read Oct. 23, 2026) confirms the city's Inclusionary Zoning rules lowered the trigger from ten units to seven. The income-restricted share rose from 13 percent to 17-20 percent, depending on building size and affordability level. Key changes took effect in October 2024. "Income-restricted" means the home's rent or sale price is capped under city rules tied to area median income (AMI).
Boston Inclusionary Zoning Rule Changes
Primary-source summary of Boston’s updated Inclusionary Zoning thresholds, set-asides, affordability levels, and effective date.
| Category | Project threshold | Set-aside requirement | Voucher access | Affordability target | Timing |
|---|---|---|---|---|---|
| Previous policy trigger threshold | ten (10) units | - | - | - | - |
| New policy trigger threshold | seven (7) units | - | - | - | - |
| Previous income-restricted share | - | 13 percent | - | - | - |
| New income-restricted share | - | 17-20 percent | - | - | - |
| Set-aside for households with mobile housing vouchers in large rental projects | - | - | three percent (3%) | - | - |
| Previous affordability requirement | - | - | - | 70% of Area Median Income (AMI) | - |
| New affordability requirement | - | - | - | average of 50% or 60% of AMI | - |
| Key changes went into effect | - | - | - | - | October 2024 |
Source:Boston.gov
That change created a cliff. Six units avoids the set-aside. Seven triggers it. That is why a small builder may stop at six even when zoning allows more, and why the 7-to-9-unit range can look risky to anyone financing it.
City Hall hasn't signaled a cut to the percentage. At a press briefing reported by the Boston Globe (Sept. 24, 2026), planning chief Kairos Shen spoke against weakening the rule. "We don't think compromising inclusionary development and compromising energy performance, climate resiliency is smart," he said. The Globe also reported that Mayor Michelle Wu "is not considering lowering the requirement."
In this example, six units is the practical ceiling for a small infill project, meaning a small development on an empty or underused lot in a built-up neighborhood.
How Does the Seventh-Unit Math Actually Work?
The Globe (Sept. 24, 2026) reports that an average inclusionary two-bedroom rents for $1,740, based on city data. It cites Apartment List for a market-rate two-bedroom at $2,550. These come from different sources, so treat the comparison as an example, not a measurement. In this hypothetical example, run the numbers:
•Six market-rate units: $15,300 a month.
•Seven units, one restricted (assumed): $17,040 a month.
In this hypothetical comparison, seven units still bring in more total rent. The problem is that, if the seventh unit costs about as much to build as the others, it adds only $1,740 a month instead of $2,550. That's an $810 monthly gap — $9,720 a year. This models rent only.
Buyers and lenders value rental buildings on income, so lower rent can cut resale or refinance value too. Whether unit seven still pencils out depends on build costs, which vary by site.
In this example, a builder may price a lot on the biggest building that still makes financial sense, not the biggest one allowed. Here, that is six units.
Six is a rule of thumb, not a fixed line. The example assumes the required share works out to one restricted unit. At 17 percent, seven units carry about 1.2 required units, and Boston's zoning text sets how a part-unit is handled. Boston.gov also says developers may, in some cases, pay into the Inclusionary Development Policy Fund instead of building income-restricted units. This example shows the on-site path only.
Why is 7 to 9 units a dead zone in this example? These projects carry the obligation without enough extra units to spread the cost. A tower with well over a hundred units can spread that cost across many market-rate homes. An eight-unit building can't. Scale may ease the problem, but only for a buyer who can assemble enough neighboring lots to build big.
There's another layer: Article 80, Boston's development review process. The Planning Department has been modernizing it, and the Zoning Commission approved a first set of amendments in August 2025, with more work planned. Larger projects can still mean more process and more carrying costs — the loan interest, taxes, and other bills a developer pays while a project sits.
Isn't the Set-Aside Just a Small Cost?
Kathy Brown of the Boston Tenants Coalition told the Globe that inclusionary zoning is "such a small cost" compared with high interest rates and construction costs. She has a point — developer Daniel Sibor also told the Globe that rates and construction costs drove much of his trouble. Those forces may be the bigger drag on Boston building overall. But the set-aside matters most at the margin, where it decides whether a project stops at six or pushes to seven.
Boston's 17-20 percent range is high next to many programs. Grounded Solutions Network's 2021 study found that 29 percent of inclusionary programs set a minimum of 20 percent or more (inclusionaryhousing.org, read Oct. 23, 2026).
Cambridge shows the strain. Sibor told the Globe he figured he would sell the market-rate condos there at close to $1,500 per square foot and the affordable units at closer to $275. In his math, market-rate buyers carry the discount. He estimated the project could have worked with an affordable share of around 8 percent, down from 20 percent.
That estimate suggests the burden depends on the chosen percentage, not only on unit seven itself. A lower set-aside percentage could shrink it. This is one Cambridge project, so it is a signal, not proof about 7-to-9-unit Boston buildings.
Could Boston change course? Sure. Construction is slumping, and policy can shift after an election, a budget squeeze, or a deeper slowdown. But the latest evidence points the other way. The Globe (Sept. 24, 2026) reports Boston, Cambridge, and Somerville "aren't budging." As of Oct. 23, 2026, the sources reviewed show no vote or timeline for a cut.
If the percentage dropped, the numbers for sites that can hold seven or more units would change the most. A price that assumes the cliff lasts forever builds in that uncertainty.
What about the new tax breaks? The Globe (Sept. 14, 2026) reports the city is offering abatements only for residential projects of 100 units or larger that cannot start for financing reasons. On Oct. 15, 2026, the Boston Planning Department's board approved agreements enabling abatements for four projects totaling about 1,400 homes. A 7-to-9-unit building falls outside that size rule, and the abatements do not change the inclusionary percentage or the lost rent on a new seven-unit building.
What Does This Mean on Your Block?
Zoning capacity is not the same as buildable value.
According to city data reported by the Globe, 2023 and 2024 were Boston's slowest years for new housing since 2011. So far, the city's answer is tax relief, not a lower set-aside.
Zoning is shifting, too. On Oct. 15, 2026, the Planning Department adopted the Cleary Square plan in Hyde Park and advanced its zoning, which still needs Zoning Commission approval for formal adoption (revised draft dated Oct. 8, 2026). But more height on paper doesn't erase the seventh-unit penalty.
For homeowners, this cuts both ways:
•Neighborhood scale may stay familiar. Triple-deckers and projects of six units or fewer stay below the seven-unit trigger.
•Small projects produce fewer affordable homes. Under the Boston.gov rules, buildings below the seven-unit trigger owe no set-aside.
•Lot offers may start with six-unit returns. Walkability, transit, and zoning still matter, but in this example the offer starts with what six units can earn.
Selling an older teardown, an oversized lot, or an underused multifamily? The biggest building zoning allows does not always carry the biggest price. A buyer prices in the risk, the timeline, the financing, and the inclusionary trigger.
What Could Change the Six-Unit Math?
Under today's rules, the numbers in this example favor six units. Several live processes could change the math before a project breaks ground.
•Selling land or a teardown? Buyers often run the numbers on a six-unit build first. A second set of numbers, at a changed trigger or percentage, shows how much of the price depends on policy. A land-use attorney can explain how the rules apply to a specific lot.
•Buying near an infill site? Nearby projects may stay modest unless a larger developer assembles enough neighboring lots to build big.
•Investing? In this example, the math favors six units, or a project large enough to spread the inclusionary cost. At 7 to 9 units, a buyer can run the numbers with a restricted unit included to test the project.
Three processes could change these numbers: the Cleary Square zoning, further Article 80 changes, and any change to the inclusionary percentage.
Have a specific Boston lot in mind? Send me the address. I'll run the numbers on a six-unit build and show where the inclusionary cliff starts.
This article is general information, not legal or tax advice. Talk to your CPA and attorney about your own situation.
