100 Summer St
100 Summer St is a 35-story building in Downtown Boston with 74% of its floor area within daylight reach of a facade. This screen estimates 856 homes and scores it 67 out of 100 for office-to-residential conversion suitability.
MA-7 & MA-8 · Screened 2026-10-04 · Worth a feasibility study
Where 100 Summer St is
Its block in Downtown Boston, drawn from Boston's own building outlines and street centerlines.
- Already housing
- Not screened
- 100 Summer St
This building does not pencil at default assumptions, even with a modeled RESIDE Act grant.
Across its 34 residential floors this building carries 282,899 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 Summer St, 2026-10-04.
| Suitability scoreWorth a feasibility study | 67 / 100 |
|---|---|
| Storiesfrom 420 ft aerial-survey height ÷ 12 ft floor-to-floor | 35 |
| Height bandsfloor plate by floor range, from the city's roof outlines | Floors 1–3: 41,906 sq ft · Floors 4–29: 35,123 sq ft · Floors 30–35: 14,861 sq ft |
| Floor platetypical floor, from the city outlines | 35,123 sq ft |
| Daylight efficiencyshare within 35 ft of a facade | 74% |
| Deepest interior pointviability threshold is 80 ft | 70 ft |
| Windowless coretypical floor; the building-wide total is in the text above | 9,545 sq ft |
| Estimated homesat 750 sq ft average | 856 |
| Conversion cost$360/sq ft all-in on 1,086,187 sq ft | $391.0M |
| Gap before grantshortfall against completed value | $13.1M |
| Modeled RESIDE grantat the statutory per-award cap | $10.0M |
| BuiltBoston's own record of the construction year | 1980 |
| 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 897 ft of exterior wall, and across 34 residential floors the building carries 28,547 ft of it in total, divided among the 856 homes this screen estimates.
Its plate is moderately compact at 0.55: 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 25.2 homes per floor, repeated on every residential floor, since this building's outline does not change as it rises.
Why 100 Summer St scores 67 out of 100
Daylight efficiency 68, Interior depth 26, Scale 100, Finance 99 — each out of 100, then weighted.
Score components for 100 Summer St. Points are the subscore times its weight.
| Component | Subscore | Weight | Points |
|---|---|---|---|
| Daylight efficiency74% of the floor area within 35 ft of a facade, scored from 40% up to 90% | 68 | 45% | 30.6 |
| Interior depthdeepest interior point 70 ft from a facade, scored from 80 ft down to 40 ft | 26 | 25% | 6.5 |
| Scale856 estimated homes, scored from 0 up to 150 | 100 | 15% | 15.0 |
| Financeremaining gap is 1% of conversion cost, scored from 60% down to 0% | 99 | 15% | 14.8 |
Most of what it earns comes from daylight efficiency, and what holds it back most is interior depth, at 26 out of 100: deepest interior point 70 ft from a facade, scored from 80 ft down to 40 ft.
Built in 1980
Boston records this building as going up in 1980, 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 74% daylight figure above deserves.
What the conversion would cost
$360 per square foot all-in across 1,086,187 sq ft of converted floor, or $391.0M in total — about $457K for each of the 856 homes.
All-in cost per square foot for 100 Summer 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 282,899 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 856 homes is $377.9M.
What would have to be true
A $13.1M gap before any grant, $3.1M after the modeled one. The smallest single change that would close it: completed value per home 1% up.
The shortfall before any grant is $13.1M. Closing it from the value side means each of the 856 homes finishing at $457K rather than the $442K the model assumes — 3% more. Closing it from the cost side means getting all-in cost down from $360 to $348 per square foot.
A modeled RESIDE grant of $10.0M moves that threshold to $445K a home. That is still above the $442K assumed, leaving $3.1M uncovered, which is why the grant does not unlock this one.
Nor do all four levers have to move. For 100 Summer St, one alone would close the gap at:
Single-assumption flip points for 100 Summer St, each holding the other three at their defaults.
| Completed value per homethe binding constraint — the least this building would need | 1% upto $445K |
|---|---|
| Average unit size | 1% downto 744 sq ft |
| Circulation efficiency | 1% upto 81% |
| Conversion cost per square foot | 1% downto $257/sq ft |
All four are sliders in the survey, where 100 Summer St re-scores against your own numbers.
How it compares in Downtown Boston
100 Summer St ranks 80th of the 96 buildings screened here, against a median score of 89.
Its floor plate is better lit than 20% of them, and shallower than 14% of them at its deepest interior point. On size it is the 10th 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
42nd of 52 zoned SKY — the comparison that shares its rules, rents and streets.
52 of the screened buildings are zoned SKY. 100 Summer St ranks 42nd 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 70 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: 15-19 Broad St
The screened building closest to 100 Summer St in converted floor area is 15-19 Broad St: 971,397 sq ft over 33 stories, against 1,086,187 sq ft over 35 here.
100 Summer St scores 67 and 15-19 Broad 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 100 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 1,800 ft apart.
Would it qualify for a RESIDE Act grant?
The model awards 100 Summer 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 Summer St
The 4 closest the screen also covers, from 230 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 230 ft away
- 105-111 Summer St6 stories · 100% daylit · 33 estimated homes · scores 88/100 (Strong candidate)about 240 ft away
- 133 Federal St13 stories · 91% daylit · 117 estimated homes · scores 90/100 (Strong candidate)about 250 ft away
- 83-87 Summer St6 stories · 90% daylit · 92 estimated homes · scores 89/100 (Strong candidate)about 300 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.