133 Federal St
133 Federal St is a 13-story building in Downtown Boston with 91% of its floor area within daylight reach of a facade. This screen estimates 117 homes and scores it 90 out of 100 for office-to-residential conversion suitability.
MA-7 & MA-8 · Screened 2026-10-04 · Strong candidate
Where 133 Federal St is
Its block in Downtown Boston, drawn from Boston's own building outlines and street centerlines.
- Already housing
- Not screened
- 133 Federal St
This building's conversion pencils at default assumptions without any subsidy.
Every floor carries 965 sq ft of windowless core — area that must be gutted, re-plumbed and sprinklered but can never be rented as an apartment. Across 12 residential floors that is 11,576 sq ft of cost carrying no revenue.
Modeled conversion metrics for 133 Federal St, 2026-10-04.
| Suitability scoreStrong candidate | 90 / 100 |
|---|---|
| Storiesfrom 155 ft aerial-survey height ÷ 12 ft floor-to-floor | 13 |
| Floor plateper floor, from the city footprint | 10,167 sq ft |
| Daylight efficiencyshare within 35 ft of a facade | 91% |
| Deepest interior pointviability threshold is 80 ft | 50 ft |
| Windowless coreper floor — renovated but never rentable | 965 sq ft |
| Estimated homesat 750 sq ft average | 117 |
| Conversion cost$360/sq ft all-in on 122,007 sq ft | $43.9M |
| Gap before grantpencils unsubsidized | -$7.7M |
| Modeled RESIDE grantbelow the statutory cap | $7.0M |
| BuiltBoston's own record of the construction year | 1959 |
| ZoningDowntown Boston | SKY |
| Opportunity Zonenot in a 2018 designated tract | No |
The plan: window line, shape and floor rhythm
40 ft of exterior wall for each home the screen estimates — enough for two- and three-bedroom homes across the plan.
The typical floor has 393 ft of exterior wall, and across 12 residential floors the building carries 4,716 ft of it in total, divided among the 117 homes this screen estimates.
Its plate is compact at 0.83: close to a square or a circle, the most efficient envelope an office can have and the least generous one for apartments: little perimeter to divide among homes. How window line and plate shape are measured.
At the model’s 750 sq ft average, the plan works out at about 9.8 homes per floor, repeated on every residential floor, since this building's outline does not change as it rises.
Why 133 Federal St scores 90 out of 100
Daylight efficiency 100, Interior depth 75, Scale 78, Finance 100 — each out of 100, then weighted.
Score components for 133 Federal St. Points are the subscore times its weight.
| Component | Subscore | Weight | Points |
|---|---|---|---|
| Daylight efficiency91% of the floor area within 35 ft of a facade, scored from 40% up to 90% | 100 | 45% | 45.0 |
| Interior depthdeepest interior point 50 ft from a facade, scored from 80 ft down to 40 ft | 75 | 25% | 18.7 |
| Scale117 estimated homes, scored from 0 up to 150 | 78 | 15% | 11.7 |
| Financecompleted value covers conversion cost with 34% 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 interior depth, at 75 out of 100: deepest interior point 50 ft from a facade, scored from 80 ft down to 40 ft.
Built in 1959
Boston records this building as going up in 1959, 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 91% daylight figure above deserves.
What the conversion would cost
$360 per square foot all-in across 122,007 sq ft of converted floor, or $43.9M in total — about $375K for each of the 117 homes.
All-in cost per square foot for 133 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 11,576 sq ft of windowless core, which has to be gutted, re-plumbed and sprinklered like the rest of the building and then earns nothing. Against it the model sets a completed value of $442K a home, which for 117 homes is $51.7M.
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 $43.9M of work with $7.7M to spare. Value per home would have to fall to $375K — 15% below the assumption — before the conversion stopped penciling, or all-in cost would have to rise from $360 to $423 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 133 Federal St:
Single-assumption flip points for 133 Federal St, each holding the other three at their defaults.
| Circulation efficiencythe binding constraint — the least this building would need | 25% downto 60% |
|---|---|
| Completed value per home | 29% downto $315K |
| Average unit size | 34% upto 1,004 sq ft |
| Conversion cost per square foot | 47% upto $381/sq ft |
All four are sliders in the survey, where 133 Federal St re-scores against your own numbers.
How it compares in Downtown Boston
133 Federal St ranks 34th of the 96 buildings screened here, against a median score of 89.
Its floor plate is better lit than 53% of them, and shallower than 47% of them at its deepest interior point. On size it is the 59th 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
16th of 52 zoned SKY — the comparison that shares its rules, rents and streets.
52 of the screened buildings are zoned SKY. 133 Federal St ranks 16th 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 50 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: 14-24 Federal St
The screened building closest to 133 Federal St in converted floor area is 14-24 Federal St: 124,503 sq ft over 11 stories, against 122,007 sq ft over 13 here.
133 Federal St scores 90 to its 98, and with the size held roughly equal most of that shortfall comes from interior depth: 75 out of 100 here, 100 there (deepest interior point 38 ft from a facade, scored from 80 ft down to 40 ft). On the money they sit in the same place: each pencils without a subsidy. The two stand about 800 ft apart.
Would it qualify for a RESIDE Act grant?
The model awards 133 Federal St $7.0M, 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 133 Federal St
The 4 closest the screen also covers, from 190 ft away. They are the colored outlines on the plan at the top of this page.
- 155 Federal St18 stories · 92% daylit · 191 estimated homes · scores 95/100 (Strong candidate)about 190 ft away
- 100 Summer St35 stories · 74% daylit · 856 estimated homes · scores 67/100 (Worth a feasibility study)about 250 ft away
- 101 Federal St31 stories · 91% daylit · 569 estimated homes · scores 93/100 (Strong candidate)about 270 ft away
- 207-211 Congress St32 stories · 82% daylit · 550 estimated homes · scores 84/100 (Strong candidate)about 330 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.