21-53 Summer St

Where 21-53 Summer St is

Its block in Downtown Boston, drawn from Boston's own building outlines and street centerlines.

The plan: window line, shape and floor rhythm

31 ft of exterior wall for each home the screen estimates — enough for two- and three-bedroom homes across the plan.

The typical floor has 1,394 ft of exterior wall, and across 10 residential floors the building carries 12,252 ft of it in total, divided among the 401 homes this screen estimates.

Its plate is moderately compact at 0.67: 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 40.1 homes per floor. Its floors are not alike, though: the typical floor's deepest interior point is 134 ft from a facade, while its worst floor reaches 136 ft. The score follows the typical floor, so a podium that could not hold a bedroom does not by itself sink a slim tower above it — but it is there, and it is part of what would have to be drawn around.

Why 21-53 Summer St scores 27 out of 100

Daylight efficiency 14, Interior depth 0, Scale 100, Finance 41 — each out of 100, then weighted.

Most of what it earns comes from scale, and what holds it back most is interior depth, at 0 out of 100: deepest interior point 134 ft from a facade, scored from 80 ft down to 40 ft.

Built in 1978

Boston records this building as going up in 1978, 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 47% daylight figure above deserves.

What the conversion would cost

$360 per square foot all-in across 802,669 sq ft of converted floor, or $289.0M in total — about $721K for each of the 401 homes.

That cost is charged across every converted square foot, including the 426,304 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 401 homes is $177.0M.

What would have to be true

A $111.9M gap before any grant, $101.9M after the modeled one. The smallest single change that would close it: average unit size 36% down.

The shortfall before any grant is $111.9M. Closing it from the value side means each of the 401 homes finishing at $721K rather than the $442K the model assumes — 63% more. Closing it from the cost side means getting all-in cost down from $360 to $221 per square foot.

A modeled RESIDE grant of $10.0M moves that threshold to $696K a home. That is still above the $442K assumed, leaving $101.9M uncovered, which is why the grant does not unlock this one.

Nor do all four levers have to move. For 21-53 Summer St, one alone would close the gap at:

All four are sliders in the survey, where 21-53 Summer St re-scores against your own numbers.

How it compares in Downtown Boston

21-53 Summer St ranks 96th of the 96 buildings screened here, against a median score of 89.

Its floor plate is better lit than 1% of them, and shallower than 1% of them at its deepest interior point. On size it is the 28th 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

52nd of 52 zoned SKY — the comparison that shares its rules, rents and streets.

52 of the screened buildings are zoned SKY. 21-53 Summer St ranks 52nd 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 134 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: 20 Rowes Whf

The screened building closest to 21-53 Summer St in converted floor area is 20 Rowes Whf: 718,946 sq ft over 18 stories, against 802,669 sq ft over 11 here.

20 Rowes Whf scores 86 and 21-53 Summer St only 27, 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 134 ft from a facade, past the 80 ft threshold beyond which conversion requires carving a light well. On the money they part ways: 20 Rowes Whf pencils without a subsidy, while 21-53 Summer St falls short even with the modeled grant. The two stand about 2,800 ft apart.

Would it qualify for a RESIDE Act grant?

The model awards 21-53 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 21-53 Summer St

The 4 closest the screen also covers, from 320 ft away. They are the colored outlines on the plan at the top of this page.

• 93-101 Arch St
  22 stories · 74% daylit · 389 estimated homes · scores 72/100 (Strong candidate)
  about 320 ft away
• 60-70 Temple Pl
  7 stories · 95% daylit · 50 estimated homes · scores 89/100 (Strong candidate)
  about 320 ft away
• 1 Avenue De Lafayette
  22 stories · 59% daylit · 721 estimated homes · scores 35/100 (Marginal)
  about 320 ft away
• 22-40 Chauncy St
  11 stories · 86% daylit · 195 estimated homes · scores 88/100 (Strong candidate)
  about 360 ft away