100 Federal St
100 Federal St is a 50-story building in Downtown Boston with 62% of its floor area within daylight reach of a facade. This screen estimates 1,164 homes and scores it 35 out of 100 for office-to-residential conversion suitability.
MA-7 & MA-8 · Screened 2026-10-04 · Marginal
Where 100 Federal St is
Its block in Downtown Boston, drawn from Boston's own building outlines and street centerlines.
- Already housing
- Not screened
- 100 Federal St
This building does not pencil at default assumptions, even with a modeled RESIDE Act grant.
Across its 49 residential floors this building carries 679,318 sq ft of windowless core — area that must be gutted, re-plumbed and sprinklered but can never be rented as an apartment.
Modeled conversion metrics for 100 Federal St, 2026-10-04.
| Suitability scoreMarginal | 35 / 100 |
|---|---|
| Storiesfrom 597 ft aerial-survey height ÷ 12 ft floor-to-floor | 50 |
| Height bandsfloor plate by floor range, from the city's roof outlines | Floors 1–19: 53,599 sq ft · Floors 20–48: 26,395 sq ft · Floors 49–50: 20,218 sq ft |
| Floor platetypical floor, from the city outlines | 53,599 sq ft |
| Daylight efficiencyshare within 35 ft of a facade | 62% |
| Deepest interior pointviability threshold is 80 ft | 92 ft |
| Windowless coretypical floor; the building-wide total is in the text above | 25,233 sq ft |
| Estimated homesat 750 sq ft average | 1,164 |
| Conversion cost$360/sq ft all-in on 1,770,665 sq ft | $637.4M |
| Gap before grantshortfall against completed value | $123.5M |
| Modeled RESIDE grantat the statutory per-award cap | $10.0M |
| BuiltBoston's own record of the construction year | 1971 |
| ZoningDowntown Boston | SKY |
| Opportunity Zonenot in a 2018 designated tract | No |
The plan: window line, shape and floor rhythm
33 ft of exterior wall for each home the screen estimates — enough for two- and three-bedroom homes across the plan.
The typical floor has 980 ft of exterior wall, and across 49 residential floors the building carries 38,613 ft of it in total, divided among the 1,164 homes this screen estimates.
Its plate is moderately compact at 0.70: 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 23.8 homes per floor, repeated on every residential floor, since this building's outline does not change as it rises.
Why 100 Federal St scores 35 out of 100
The weighted components add to 45, but the score is capped at 35 because its deepest interior point is 92 ft from a facade, past the 80 ft threshold beyond which conversion requires carving a light well.
Score components for 100 Federal St. Points are the subscore times its weight.
| Component | Subscore | Weight | Points |
|---|---|---|---|
| Daylight efficiency62% of the floor area within 35 ft of a facade, scored from 40% up to 90% | 43 | 45% | 19.5 |
| Interior depthdeepest interior point 92 ft from a facade, scored from 80 ft down to 40 ft | 0 | 25% | 0.0 |
| Scale1164 estimated homes, scored from 0 up to 150 | 100 | 15% | 15.0 |
| Financeremaining gap is 18% of conversion cost, scored from 60% down to 0% | 70 | 15% | 10.5 |
Most of what it earns comes from daylight efficiency, and what holds it back most is interior depth, at 0 out of 100: deepest interior point 92 ft from a facade, scored from 80 ft down to 40 ft.
Built in 1971
Boston records this building as going up in 1971, which puts it in the late-modern stock.
As a rule, typically the hardest to convert: the deepest plates of any era, large central cores, and floor-to-floor heights tight enough that running residential drainage under a ceiling can be the thing that ends a project. 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 62% daylight figure above deserves.
What the conversion would cost
$360 per square foot all-in across 1,770,665 sq ft of converted floor, or $637.4M in total — about $548K for each of the 1,164 homes.
All-in cost per square foot for 100 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 679,318 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 1,164 homes is $513.9M.
What would have to be true
A $123.5M gap before any grant, $113.5M after the modeled one. The smallest single change that would close it: average unit size 18% down.
The shortfall before any grant is $123.5M. Closing it from the value side means each of the 1,164 homes finishing at $548K rather than the $442K the model assumes — 24% more. Closing it from the cost side means getting all-in cost down from $360 to $290 per square foot.
A modeled RESIDE grant of $10.0M moves that threshold to $539K a home. That is still above the $442K assumed, leaving $113.5M uncovered, which is why the grant does not unlock this one.
Nor do all four levers have to move. For 100 Federal St, one alone would close the gap at:
Single-assumption flip points for 100 Federal St, each holding the other three at their defaults.
| Average unit sizethe binding constraint — the least this building would need | 18% downto 614 sq ft |
|---|---|
| Completed value per home | 22% upto $539K |
| Circulation efficiency | 22% upto 98% |
| Conversion cost per square foot | 25% downto $196/sq ft |
All four are sliders in the survey, where 100 Federal St re-scores against your own numbers.
How it compares in Downtown Boston
100 Federal St ranks 90th of the 96 buildings screened here, against a median score of 89.
Its floor plate is better lit than 6% of them, and shallower than 7% of them at its deepest interior point. On size it is the 2nd 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
47th of 52 zoned SKY — the comparison that shares its rules, rents and streets.
52 of the screened buildings are zoned SKY. 100 Federal St ranks 47th 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 92 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: 669-671 Atlantic Ave
The screened building closest to 100 Federal St in converted floor area is 669-671 Atlantic Ave: 1,419,426 sq ft over 49 stories, against 1,770,665 sq ft over 50 here.
669-671 Atlantic Ave scores 63 and 100 Federal St only 35, and the difference is a hard fail rather than a matter of degree: the lower one is capped at 35 because its deepest interior point is 92 ft from a facade, past the 80 ft threshold beyond which conversion requires carving a light well. On the money they sit in the same place: each falls short even with the modeled grant. The two stand about 1,000 ft apart.
Would it qualify for a RESIDE Act grant?
The model awards 100 Federal St $10.0M, 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 100 Federal St
The 4 closest the screen also covers, from 240 ft away. They are the colored outlines on the plan at the top of this page.
- 70 Federal St9 stories · 100% daylit · 60 estimated homes · scores 91/100 (Strong candidate)about 240 ft away
- 101 Federal St31 stories · 91% daylit · 569 estimated homes · scores 93/100 (Strong candidate)about 240 ft away
- 207-211 Congress St32 stories · 82% daylit · 550 estimated homes · scores 84/100 (Strong candidate)about 250 ft away
- 75-101 Federal St21 stories · 89% daylit · 257 estimated homes · scores 96/100 (Strong candidate)about 280 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.