20 Ashburton Pl

20 Ashburton Pl is a 8-story building in Downtown Boston with 99% of its floor area within daylight reach of a facade. This screen estimates 78 homes and scores it 93 out of 100 for office-to-residential conversion suitability.

MA-7 & MA-8 · Screened 2026-10-04 · Strong candidate

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Also addressed as 122-126 Bowdoin St: Boston’s address records place both on this one footprint.

Where 20 Ashburton Pl is

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

Suitability score

0–29

30–49

50–69

70–100

Already housing
Not screened
20 Ashburton Pl

20 Ashburton Pl and the 1,000 ft of Downtown Boston around it. The streets are drawn at the width of the right-of-way they run down, sidewalks included, and named, and every building on these blocks is drawn. What is left open and stippled is neither: a surface lot, a plaza or a vacant parcel. The screened buildings are colored by the ramp above, the same one the district map uses, carry their score, and each is a link to its own page. Each casts a shadow as long as its measured height lets it, so towers stand out from the low buildings around them; the unscreened buildings have no measured height and cast none. 20 Ashburton Pl is outlined in its own score color at the outline it covers at ground level. Its windowless core is hatched. The inset places it among every building the screen covers.

Floor plan: 99% of each floor sits within daylight reach of a facade. The shading is daylight, darkest at the windows and gone 35 ft in. The hatched area is windowless core: 56 sq ft per floor that must be renovated but can never be rented as an apartment. The dimension marks the deepest interior point, 38 ft from the nearest window. A–A is where the section beside it is cut.

Section A–A: cut across the depth of the plate, through the middle of the core. Daylight reaches 35 ft in from every facade, fading as it goes, and the hatched stripe left between the lit edges is floor that gets converted and can never be rented: 56 sq ft on the floor the screen scores, and 389 sq ft over 7 residential floors. The shaded ground floor is converted like the rest and counted as no homes.

This building's conversion pencils at default assumptions without any subsidy.

Every floor carries 56 sq ft of windowless core — area that must be gutted, re-plumbed and sprinklered but can never be rented as an apartment. Across 7 residential floors that is 389 sq ft of cost carrying no revenue.

Modeled conversion metrics for 20 Ashburton Pl, 2026-10-04.

Suitability scoreStrong candidate	93 / 100
Storiesfrom 100 ft aerial-survey height ÷ 12 ft floor-to-floor	8
Floor plateper floor, from the city footprint	10,572 sq ft
Daylight efficiencyshare within 35 ft of a facade	99%
Deepest interior pointviability threshold is 80 ft	38 ft
Windowless coreper floor — renovated but never rentable	56 sq ft
Estimated homesat 750 sq ft average	78
Conversion cost$360/sq ft all-in on 74,007 sq ft	$26.6M
Gap before grantpencils unsubsidized	-$7.8M
Modeled RESIDE grantbelow the statutory cap	$4.7M
BuiltBoston's own record of the construction year	1968
ZoningDowntown Boston	PEMBERTON SQUARE PROTECTION AREA
Opportunity Zonenot in a 2018 designated tract	No

The plan: window line, shape and floor rhythm

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

The typical floor has 504 ft of exterior wall, and across 7 residential floors the building carries 3,526 ft of it in total, divided among the 78 homes this screen estimates.

Its plate is moderately compact at 0.52: 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 11.1 homes per floor, repeated on every residential floor, since this building's outline does not change as it rises.

Why 20 Ashburton Pl scores 93 out of 100

Daylight efficiency 100, Interior depth 100, Scale 52, Finance 100 — each out of 100, then weighted.

Score components for 20 Ashburton Pl. Points are the subscore times its weight.

Component	Subscore	Weight	Points
Daylight efficiency99% of the floor area within 35 ft of a facade, scored from 40% up to 90%	100	45%	45.0
Interior depthdeepest interior point 38 ft from a facade, scored from 80 ft down to 40 ft	100	25%	25.0
Scale78 estimated homes, scored from 0 up to 150	52	15%	7.8
Financecompleted value covers conversion cost with 47% 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 52 out of 100: 78 estimated homes, scored from 0 up to 150.

Built in 1968

Boston records this building as going up in 1968, 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 99% daylight figure above deserves.

What the conversion would cost

$360 per square foot all-in across 74,007 sq ft of converted floor, or $26.6M in total — about $342K for each of the 78 homes.

All-in cost per square foot for 20 Ashburton Pl: 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 389 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 78 homes is $34.4M.

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 $26.6M of work with $7.8M to spare. Value per home would have to fall to $342K — 23% below the assumption — before the conversion stopped penciling, or all-in cost would have to rise from $360 to $465 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 20 Ashburton Pl:

Single-assumption flip points for 20 Ashburton Pl, each holding the other three at their defaults.

Circulation efficiencythe binding constraint — the least this building would need	31% downto 55%
Completed value per home	36% downto $282K
Average unit size	45% upto 1,091 sq ft
Conversion cost per square foot	65% upto $429/sq ft

All four are sliders in the survey, where 20 Ashburton Pl re-scores against your own numbers.

How it compares in Downtown Boston

20 Ashburton Pl ranks 20th of the 96 buildings screened here, against a median score of 89.

Its floor plate is better lit than 77% of them, and shallower than 74% of them at its deepest interior point. On size it is the 74th 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 PEMBERTON SQUARE PROTECTION AREA zone

2nd of 7 zoned PEMBERTON SQUARE PROTECTION AREA — the comparison that shares its rules, rents and streets.

7 of the screened buildings are zoned PEMBERTON SQUARE PROTECTION AREA. 20 Ashburton Pl ranks 2nd of them against a median score of 79. 5 score 70 or more, their median deepest interior point is 60 ft from a facade against this building’s 38 ft, and together they would hold an estimated 2,645 homes. The group’s top scorer is 6-6B Beacon St, at 94.

Its nearest match in size: 77 Franklin St

The screened building closest to 20 Ashburton Pl in converted floor area is 77 Franklin St: 73,070 sq ft over 11 stories, against 74,007 sq ft over 8 here.

The two land within a few points of each other — 93 here, 93 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 1,800 ft apart.

Would it qualify for a RESIDE Act grant?

The model awards 20 Ashburton Pl $4.7M, 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 20 Ashburton Pl

The 4 closest the screen also covers, from 220 ft away. They are the colored outlines on the plan at the top of this page.

21-23 Beacon St
10 stories · 83% daylit · already a condominium building
about 220 ft away
12-14A Beacon St
9 stories · 100% daylit · 85 estimated homes · scores 94/100 (Strong candidate)
about 410 ft away
6-6B Beacon St
10 stories · 100% daylit · 92 estimated homes · scores 94/100 (Strong candidate)
about 420 ft away
1 Beacon St
42 stories · 65% daylit · 881 estimated homes · scores 55/100 (Worth a feasibility study)
about 490 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.