2131 Arch St
2131 Arch St is a 4-story building in Center City Philadelphia with 93% of its floor area within daylight reach of a facade. This screen estimates 27 homes and scores it 76 out of 100 for office-to-residential conversion suitability.
PA-2 & PA-3 · Screened 2026-09-15 · Strong candidate
Also addressed as 2133 Arch St, 2135 Arch St, 2137 Arch St, 2139 Arch St and 2141 Arch St: Philadelphia’s address records place all 6 on this one footprint.
Where 2131 Arch St is
Its block in Center City Philadelphia, drawn from Philadelphia's own building outlines and street centerlines.
- Already housing
- Not screened
- 2131 Arch St
This building does not pencil at default assumptions, even with a modeled RESIDE Act grant.
Every floor carries 651 sq ft of windowless core — area that must be gutted, re-plumbed and sprinklered but can never be rented as an apartment. Across 3 residential floors that is 1,954 sq ft of cost carrying no revenue.
Modeled conversion metrics for 2131 Arch St, 2026-09-15.
| Suitability scoreStrong candidate | 76 / 100 |
|---|---|
| Storiesfrom 61 ft LiDAR height ÷ 12 ft floor-to-floor | 4 |
| Floor plateper floor, from the city footprint | 9,193 sq ft |
| Daylight efficiencyshare within 35 ft of a facade | 93% |
| Deepest interior pointviability threshold is 80 ft | 47 ft |
| Windowless coreper floor — renovated but never rentable | 651 sq ft |
| Estimated homesat 750 sq ft average | 27 |
| Conversion cost$360/sq ft all-in on 27,579 sq ft | $9.9M |
| Gap before grantshortfall against completed value | $4.6M |
| Modeled RESIDE grantbelow the statutory cap | $1.6M |
| BuiltPhiladelphia's own record of the construction year | 1908 |
| ZoningCenter City Philadelphia | CMX2 |
| Opportunity Zonenot in a 2018 designated tract | No |
The plan: window line, shape and floor rhythm
43 ft of exterior wall for each home the screen estimates — enough for two- and three-bedroom homes across the plan.
The typical floor has 389 ft of exterior wall, and across 3 residential floors the building carries 1,168 ft of it in total, divided among the 27 homes this screen estimates.
Its plate is compact at 0.76: 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 9.0 homes per floor, repeated on every residential floor, since this building's outline does not change as it rises.
Why 2131 Arch St scores 76 out of 100
Daylight efficiency 100, Interior depth 83, Scale 18, Finance 50 — each out of 100, then weighted.
Score components for 2131 Arch St. Points are the subscore times its weight.
| Component | Subscore | Weight | Points |
|---|---|---|---|
| Daylight efficiency93% of the floor area within 35 ft of a facade, scored from 40% up to 90% | 100 | 45% | 45.0 |
| Interior depthdeepest interior point 47 ft from a facade, scored from 80 ft down to 40 ft | 83 | 25% | 20.7 |
| Scale27 estimated homes, scored from 0 up to 150 | 18 | 15% | 2.7 |
| Financeremaining gap is 30% of conversion cost, scored from 60% down to 0% | 50 | 15% | 7.5 |
Most of what it earns comes from daylight efficiency, and what holds it back most is scale, at 18 out of 100: 27 estimated homes, scored from 0 up to 150.
Built in 1908
Philadelphia records this building as going up in 1908, which puts it in the pre-1920 stock.
As a rule, the era that converts most readily: load-bearing masonry, small floor plates laid out before deep-plan offices were possible, operable windows and generous floor-to-floor heights. The usual obstacles are not daylight but hazardous materials, lifts and bringing structure up to current code. 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 93% daylight figure above deserves.
What the conversion would cost
$360 per square foot all-in across 27,579 sq ft of converted floor, or $9.9M in total — about $368K for each of the 27 homes.
All-in cost per square foot for 2131 Arch 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 1,954 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 $197K a home, which for 27 homes is $5.3M.
What would have to be true
A $4.6M gap before any grant, $3.0M after the modeled one. The smallest single change that would close it: average unit size 30% down.
The shortfall before any grant is $4.6M. Closing it from the value side means each of the 27 homes finishing at $368K rather than the $197K the model assumes — 87% more. Closing it from the cost side means getting all-in cost down from $360 to $193 per square foot.
A modeled RESIDE grant of $1.6M moves that threshold to $308K a home. That is still above the $197K assumed, leaving $3.0M uncovered, which is why the grant does not unlock this one.
Nor do all four levers have to move. For 2131 Arch St, one alone would close the gap at:
Single-assumption flip points for 2131 Arch St, each holding the other three at their defaults.
| Average unit sizethe binding constraint — the least this building would need | 30% downto 526 sq ft |
|---|---|
| Conversion cost per square foot | 42% downto $151/sq ft |
| Completed value per home | 56% upto $308K |
All four are sliders in the survey, where 2131 Arch St re-scores against your own numbers.
How it compares in Center City Philadelphia
2131 Arch St ranks 41st of the 103 buildings screened here, against a median score of 67.
Its floor plate is better lit than 71% of them, and shallower than 65% of them at its deepest interior point. On size it is the 102nd largest by estimated homes. The full survey of all 103 buildings ranks and maps every one of them, and the list by address links each to its own page.
Its nearest match in size: 15 S 11th St
The screened building closest to 2131 Arch St in converted floor area is 15 S 11th St: 26,674 sq ft over 5 stories, against 27,579 sq ft over 4 here.
2131 Arch St scores 76 to its 81, and with the size held roughly equal most of that shortfall comes from interior depth: 83 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 falls short even with the modeled grant. The two stand about 5,300 ft apart.
Would it qualify for a RESIDE Act grant?
The model awards 2131 Arch St $1.6M, 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 2131 Arch St
The 4 closest the screen also covers, from 780 ft away. They are the colored outlines on the plan at the top of this page.
- 100 N 20th St5 stories · 74% daylit · 69 estimated homes · scores 48/100 (Marginal)about 780 ft away
- 2005 Market St40 stories · 61% daylit · 1,337 estimated homes · scores 34/100 (Marginal)about 800 ft away
- 2301 Market St35 stories · 52% daylit · 1,623 estimated homes · scores 26/100 (Unlikely)about 890 ft away
- 2001 Market St41 stories · 60% daylit · 1,351 estimated homes · scores 33/100 (Marginal)about 990 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.