70 Federal St
70 Federal St is a 9-story building in Downtown Boston with 100% of its floor area within daylight reach of a facade. This screen estimates 60 homes and scores it 91 out of 100 for office-to-residential conversion suitability.
MA-7 & MA-8 · Screened 2026-10-04 · Strong candidate
Where 70 Federal St is
Its block in Downtown Boston, drawn from Boston's own building outlines and street centerlines.
- Already housing
- Not screened
- 70 Federal St
This building's conversion pencils at default assumptions without any subsidy.
This footprint has no windowless core at all: every point on the floor plate is within 35 ft of a facade, which is unusual and is the main reason it scores as well as it does.
Modeled conversion metrics for 70 Federal St, 2026-10-04.
| Suitability scoreStrong candidate | 91 / 100 |
|---|---|
| Storiesfrom 104 ft aerial-survey height ÷ 12 ft floor-to-floor | 9 |
| Height bandsfloor plate by floor range, from the city's roof outlines | Floors 1–7: 8,243 sq ft · Floors 8–9: 3,509 sq ft |
| Floor platetypical floor, from the city outlines | 8,243 sq ft |
| Daylight efficiencyshare within 35 ft of a facade | 100% |
| Deepest interior pointviability threshold is 80 ft | 31 ft |
| Windowless coretypical floor; the building-wide total is in the text above | 0 sq ft |
| Estimated homesat 750 sq ft average | 60 |
| Conversion cost$360/sq ft all-in on 56,476 sq ft | $20.3M |
| Gap before grantpencils unsubsidized | -$6.2M |
| Modeled RESIDE grantbelow the statutory cap | $3.6M |
| BuiltBoston's own record of the construction year | 1966 |
| ZoningDowntown Boston | SKY |
| Opportunity Zonenot in a 2018 designated tract | No |
The plan: window line, shape and floor rhythm
47 ft of exterior wall for each home the screen estimates — enough for two- and three-bedroom homes across the plan.
The typical floor has 387 ft of exterior wall, and across 8 residential floors the building carries 2,804 ft of it in total, divided among the 60 homes this screen estimates.
Its plate is moderately compact at 0.69: a squarish plan, with enough perimeter for a conventional double-loaded corridor. How window line and plate shape are measured.
At the model’s 750 sq ft average, the plan works out at about 7.5 homes per floor, repeated on every residential floor, since this building's outline does not change as it rises.
Why 70 Federal St scores 91 out of 100
Daylight efficiency 100, Interior depth 100, Scale 40, Finance 100 — each out of 100, then weighted.
Score components for 70 Federal St. Points are the subscore times its weight.
| Component | Subscore | Weight | Points |
|---|---|---|---|
| Daylight efficiency100% of the floor area within 35 ft of a facade, scored from 40% up to 90% | 100 | 45% | 45.0 |
| Interior depthdeepest interior point 31 ft from a facade, scored from 80 ft down to 40 ft | 100 | 25% | 25.0 |
| Scale60 estimated homes, scored from 0 up to 150 | 40 | 15% | 6.0 |
| Financecompleted value covers conversion cost with 48% to spare, which tops out the component | 100 | 15% | 15.0 |
Most of what it earns comes from daylight efficiency, and what holds it back most is scale, at 40 out of 100: 60 estimated homes, scored from 0 up to 150.
Built in 1966
Boston records this building as going up in 1966, which puts it in the post-war stock.
As a rule, the period when plates got deep and facades became curtain wall: sealed glazing, lower floor-to-floor heights, and mechanical systems designed around a sealed box. Conversions here usually turn on whether the windows can be made to open and whether ceilings survive new plumbing. That is the era’s general tendency rather than a finding about this building — the model reads an outline and a height, and can see nothing inside — but it is the first thing an architect would want to know, and it colours how much confidence the 100% daylight figure above deserves.
What the conversion would cost
$360 per square foot all-in across 56,476 sq ft of converted floor, or $20.3M in total — about $339K for each of the 60 homes.
All-in cost per square foot for 70 Federal St: base cost plus the code work a change of use triggers.
| Base conversion cost | $260/sq ft |
|---|---|
| Plumbing risers to every unit | $40/sq ft |
| Operable windows and glazing | $30/sq ft |
| Additional egress stair | $18/sq ft |
| Fire sprinklers (NFPA 13R) | $12/sq ft |
| All-in | $360/sq ft |
That cost is charged across every converted square foot, including the circulation and service area that earns nothing directly. Against it the model sets a completed value of $442K a home, which for 60 homes is $26.5M.
What would have to be true
This one already clears the bar. The question is how much room it has before it stops.
At $442K a home, completed value covers the $20.3M of work with $6.2M to spare. Value per home would have to fall to $339K — 23% below the assumption — before the conversion stopped penciling, or all-in cost would have to rise from $360 to $469 per square foot. Neither is a wide margin in a market that moves, but this building does not need a grant to work.
Each of these, moved on its own, would be enough to undo that for 70 Federal St:
Single-assumption flip points for 70 Federal St, each holding the other three at their defaults.
| Circulation efficiencythe binding constraint — the least this building would need | 32% downto 54% |
|---|---|
| Completed value per home | 37% downto $279K |
| Average unit size | 47% upto 1,102 sq ft |
| Conversion cost per square foot | 66% upto $433/sq ft |
All four are sliders in the survey, where 70 Federal St re-scores against your own numbers.
How it compares in Downtown Boston
70 Federal St ranks 30th of the 96 buildings screened here, against a median score of 89.
Its floor plate is better lit than 100% of them, and shallower than 89% of them at its deepest interior point. On size it is the 83rd largest by estimated homes. The full survey of all 96 buildings ranks and maps every one of them, and the list by address links each to its own page.
Within the SKY zone
14th of 52 zoned SKY — the comparison that shares its rules, rents and streets.
52 of the screened buildings are zoned SKY. 70 Federal St ranks 14th of them against a median score of 88. 40 score 70 or more, their median deepest interior point is 51 ft from a facade against this building’s 31 ft, and together they would hold an estimated 19,019 homes. The group’s top scorer is 147 Milk St, at 100.
Its nearest match in size: 100 City Hall Plz
The screened building closest to 70 Federal St in converted floor area is 100 City Hall Plz: 54,738 sq ft over 7 stories, against 56,476 sq ft over 9 here.
The two land within a few points of each other — 91 here, 91 there — so at this size the screen reads them as much the same prospect. On the money they sit in the same place: each pencils without a subsidy. The two stand about 1,500 ft apart.
Would it qualify for a RESIDE Act grant?
The model awards 70 Federal St $3.6M, on the assumption it qualifies. Whether it does, no published dataset can say.
That figure assumes the building meets the Act’s vacant-and-abandoned test, which turns on code-enforcement and receivership records no city publishes.
It does not sit in a 2018 designated Opportunity Zone, so it would not draw that Section 201 priority.
Other buildings screened near 70 Federal St
The 4 closest the screen also covers, from 80 ft away. They are the colored outlines on the plan at the top of this page.
- 42-60 Federal St10 stories · 92% daylit · 81 estimated homes · scores 89/100 (Strong candidate)about 80 ft away
- 125-135 Congress St8 stories · 98% daylit · 49 estimated homes · scores 90/100 (Strong candidate)about 160 ft away
- 100 Federal St50 stories · 62% daylit · 1,164 estimated homes · scores 35/100 (Marginal)about 240 ft away
- 1 Federal St43 stories · 68% daylit · 916 estimated homes · scores 62/100 (Worth a feasibility study)about 260 ft away
A screen, not a feasibility study, from outlines and heights rather than plans: the method and how to correct a figure. If you know this building’s interior, you know what this model cannot see.