508 Walnut St

Where 508 Walnut St is

Its block in Center City Philadelphia, drawn from Philadelphia's own building outlines and street centerlines.

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 1,196 ft of exterior wall, and across 19 residential floors the building carries 22,716 ft of it in total, divided among the 712 homes this screen estimates.

Its plate is moderately compact at 0.64: 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 37.5 homes per floor, repeated on every residential floor, since this building's outline does not change as it rises.

Why 508 Walnut St scores 23 out of 100

Daylight efficiency 17, Interior depth 0, Scale 100, Finance 0 — 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 104 ft from a facade, scored from 80 ft down to 40 ft.

Built in 1918

Philadelphia records this building as going up in 1918, 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 48% daylight figure above deserves.

What the conversion would cost

$360 per square foot all-in across 1,379,079 sq ft of converted floor, or $496.5M in total — about $697K for each of the 712 homes.

That cost is charged across every converted square foot, including the 710,985 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 712 homes is $140.1M.

What would have to be true

A $356.4M gap before any grant, $346.4M after the modeled one. The smallest single change that would close it: average unit size 71% down.

The shortfall before any grant is $356.4M. Closing it from the value side means each of the 712 homes finishing at $697K rather than the $197K the model assumes — 254% more. Closing it from the cost side means getting all-in cost down from $360 to $102 per square foot.

A modeled RESIDE grant of $10.0M moves that threshold to $683K a home. That is still above the $197K assumed, leaving $346.4M uncovered, which is why the grant does not unlock this one.

Nor do all four levers have to move. For 508 Walnut St, one alone would close the gap at:

All four are sliders in the survey, where 508 Walnut St re-scores against your own numbers.

How it compares in Center City Philadelphia

508 Walnut St ranks 99th of the 103 buildings screened here, against a median score of 67.

Its floor plate is better lit than 5% of them, and shallower than 6% of them at its deepest interior point. On size it is the 14th 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.

Within the CMX4 zone

14th of 15 zoned CMX4 — the comparison that shares its rules, rents and streets.

15 of the screened buildings are zoned CMX4. 508 Walnut St ranks 14th of them against a median score of 58. 5 score 70 or more, their median deepest interior point is 64 ft from a facade against this building’s 104 ft, and together they would hold an estimated 4,016 homes. The group’s top scorer is 901 Arch St, at 84.

Its nearest match in size: 1500 Spring Garden St

The screened building closest to 508 Walnut St in converted floor area is 1500 Spring Garden St: 1,364,796 sq ft over 12 stories, against 1,379,079 sq ft over 20 here.

508 Walnut St scores 23 to its 16, and with the size held roughly equal most of that lead comes from daylight efficiency: 17 out of 100 here, 1 there (41% 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 6,600 ft apart.

Would it qualify for a RESIDE Act grant?

The model awards 508 Walnut 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 508 Walnut St

The 4 closest the screen also covers, from 350 ft away. They are the colored outlines on the plan at the top of this page.

• 428 Walnut St
  9 stories · 74% daylit · 212 estimated homes · scores 58/100 (Worth a feasibility study)
  about 350 ft away
• 170 S Independence Mall W
  12 stories · 43% daylit · 476 estimated homes · scores 18/100 (Unlikely)
  about 490 ft away
• 105 S 7th St
  4 stories · 63% daylit · 66 estimated homes · scores 33/100 (Marginal)
  about 710 ft away
• 700 Chestnut St
  6 stories · 100% daylit · 36 estimated homes · scores 83/100 (Strong candidate)
  about 900 ft away