801 Arch St
801 Arch St is a 6-story building in Center City Philadelphia with 71% of its floor area within daylight reach of a facade. This screen estimates 133 homes and scores it 56 out of 100 for office-to-residential conversion suitability.
PA-2 & PA-3 · Screened 2026-09-15 · Worth a feasibility study
Where 801 Arch St is
Its block in Center City Philadelphia, drawn from Philadelphia's own building outlines and street centerlines.
- Already housing
- Not screened
- 801 Arch St
This building does not pencil at default assumptions, even with a modeled RESIDE Act grant.
Every floor carries 10,257 sq ft of windowless core — area that must be gutted, re-plumbed and sprinklered but can never be rented as an apartment. Across 5 residential floors that is 51,286 sq ft of cost carrying no revenue.
Modeled conversion metrics for 801 Arch St, 2026-09-15.
| Suitability scoreWorth a feasibility study | 56 / 100 |
|---|---|
| Storiesfrom 95 ft LiDAR height ÷ 12 ft floor-to-floor | 6 |
| Floor plateper floor, from the city footprint | 35,219 sq ft |
| Daylight efficiencyshare within 35 ft of a facade | 71% |
| Deepest interior pointviability threshold is 80 ft | 61 ft |
| Windowless coreper floor — renovated but never rentable | 10,257 sq ft |
| Estimated homesat 750 sq ft average | 133 |
| Conversion cost$360/sq ft all-in on 176,095 sq ft | $63.4M |
| Gap before grantshortfall against completed value | $37.2M |
| Modeled RESIDE grantbelow the statutory cap | $8.0M |
| BuiltPhiladelphia's own record of the construction year | 1975 |
| ZoningCenter City Philadelphia | ICMX |
| Opportunity Zonecensus tract 42101000200, 2018 designation | Yes |
The plan: window line, shape and floor rhythm
32 ft of exterior wall for each home the screen estimates — enough for two- and three-bedroom homes across the plan.
The typical floor has 862 ft of exterior wall, and across 5 residential floors the building carries 4,310 ft of it in total, divided among the 133 homes this screen estimates.
Its plate is moderately compact at 0.60: 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 26.6 homes per floor, repeated on every residential floor, since this building's outline does not change as it rises.
Why 801 Arch St scores 56 out of 100
Daylight efficiency 62, Interior depth 47, Scale 89, Finance 23 — each out of 100, then weighted.
Score components for 801 Arch St. Points are the subscore times its weight.
| Component | Subscore | Weight | Points |
|---|---|---|---|
| Daylight efficiency71% of the floor area within 35 ft of a facade, scored from 40% up to 90% | 62 | 45% | 27.8 |
| Interior depthdeepest interior point 61 ft from a facade, scored from 80 ft down to 40 ft | 47 | 25% | 11.7 |
| Scale133 estimated homes, scored from 0 up to 150 | 89 | 15% | 13.3 |
| Financeremaining gap is 46% of conversion cost, scored from 60% down to 0% | 23 | 15% | 3.5 |
Most of what it earns comes from daylight efficiency, and what holds it back most is finance, at 23 out of 100: remaining gap is 46% of conversion cost, scored from 60% down to 0%.
Built in 1975
Philadelphia records this building as going up in 1975, 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 71% daylight figure above deserves.
What the conversion would cost
$360 per square foot all-in across 176,095 sq ft of converted floor, or $63.4M in total — about $477K for each of the 133 homes.
All-in cost per square foot for 801 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 51,286 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 133 homes is $26.2M.
What would have to be true
A $37.2M gap before any grant, $29.3M after the modeled one. The smallest single change that would close it: average unit size 51% down.
The shortfall before any grant is $37.2M. Closing it from the value side means each of the 133 homes finishing at $477K rather than the $197K the model assumes — 142% more. Closing it from the cost side means getting all-in cost down from $360 to $149 per square foot.
A modeled RESIDE grant of $8.0M moves that threshold to $417K a home. That is still above the $197K assumed, leaving $29.3M uncovered, which is why the grant does not unlock this one.
Nor do all four levers have to move. For 801 Arch St, one alone would close the gap at:
Single-assumption flip points for 801 Arch St, each holding the other three at their defaults.
| Average unit sizethe binding constraint — the least this building would need | 51% downto 367 sq ft |
|---|---|
| Conversion cost per square foot | 64% downto $94/sq ft |
| Completed value per home | 112% upto $417K |
All four are sliders in the survey, where 801 Arch St re-scores against your own numbers.
How it compares in Center City Philadelphia
801 Arch St ranks 61st of the 103 buildings screened here, against a median score of 67.
Its floor plate is better lit than 37% of them, and shallower than 46% of them at its deepest interior point. On size it is the 62nd 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: 309 Callowhill St
The screened building closest to 801 Arch St in converted floor area is 309 Callowhill St: 182,203 sq ft over 6 stories, against 176,095 sq ft over 6 here.
801 Arch St scores 56 to its 62, and with the size held roughly equal most of that shortfall comes from daylight efficiency: 62 out of 100 here, 71 there (76% of the floor area within 35 ft of a facade, scored from 40% up to 90%). On the money they sit in the same place: each falls short even with the modeled grant. The two stand about 2,900 ft apart.
Would it qualify for a RESIDE Act grant?
The model awards 801 Arch St $8.0M, 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.
This building does sit in census tract 42101000200, a 2018 designated Opportunity Zone, which Section 201 lets HUD favor — one of the few statutory priorities this screen can actually check.
Other buildings screened near 801 Arch St
The 4 closest the screen also covers, from 190 ft away. They are the colored outlines on the plan at the top of this page.
- 117 N 8th St8 stories · 95% daylit · 63 estimated homes · scores 84/100 (Strong candidate)about 190 ft away
- 901 Arch St7 stories · 100% daylit · 47 estimated homes · scores 84/100 (Strong candidate)about 400 ft away
- 736 Arch St7 stories · 97% daylit · 129 estimated homes · scores 91/100 (Strong candidate)about 440 ft away
- 701 Market St5 stories · 40% daylit · 247 estimated homes · scores 15/100 (Unlikely)about 750 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.