81 Post St

81 Post St is a 9-story building in Downtown San Jose with 100% of its floor area within daylight reach of a facade. This screen estimates 51 homes and scores it 90 out of 100 for office-to-residential conversion suitability.

CA-18 · Screened 2026-09-12 · Strong candidate

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Also addressed as 34 S Market St and 40 S Market St: San Jose’s address records place all 3 on this one footprint.

Where 81 Post St is

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

Suitability score

0–29

30–49

50–69

70–100

Already housing
Not screened
81 Post St

81 Post St and the 1,000 ft of Downtown San Jose 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. 81 Post St is outlined in its own score color at the outline it covers at ground level. The inset places it among every building the screen covers.

Floor plan: 100% of each floor sits within daylight reach of a facade, with no dead core at all. The shading is daylight, darkest at the windows and gone 35 ft in. The dimension marks the deepest interior point, 30 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, and here it meets in the middle: the plate is thin enough that no floor is left windowless. 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.

This footprint has no windowless core at all: every point on the floor plate is within 35 ft of a facade, which is unusual and is the main reason it scores as well as it does.

Modeled conversion metrics for 81 Post St, 2026-09-12.

Suitability scoreStrong candidate	90 / 100
Storiesfrom 108 ft LiDAR height ÷ 12 ft floor-to-floor	9
Floor plateper floor, from the city footprint	6,055 sq ft
Daylight efficiencyshare within 35 ft of a facade	100%
Deepest interior pointviability threshold is 80 ft	30 ft
Windowless coreper floor — renovated but never rentable	0 sq ft
Estimated homesat 750 sq ft average	51
Conversion cost$405/sq ft all-in on 48,443 sq ft	$19.6M
Gap before grantpencils unsubsidized	-$2.1M
Modeled RESIDE grantbelow the statutory cap	$3.1M
BuiltSan Jose does not publish a construction year with this data	—
ZoningDowntown San Jose	DC
Opportunity Zonecensus tract 06085500800, 2018 designation	Yes

The plan: window line, shape and floor rhythm

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

The typical floor has 322 ft of exterior wall, and across 8 residential floors the building carries 2,575 ft of it in total, divided among the 51 homes this screen estimates.

Its plate is compact at 0.73: 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 6.4 homes per floor, repeated on every residential floor, since this building's outline does not change as it rises.

Why 81 Post St scores 90 out of 100

Daylight efficiency 100, Interior depth 100, Scale 34, Finance 100 — each out of 100, then weighted.

Score components for 81 Post St. Points are the subscore times its weight.

Component	Subscore	Weight	Points
Daylight efficiency100% of the floor area within 35 ft of a facade, scored from 40% up to 90%	100	45%	45.0
Interior depthdeepest interior point 30 ft from a facade, scored from 80 ft down to 40 ft	100	25%	25.0
Scale51 estimated homes, scored from 0 up to 150	34	15%	5.1
Financecompleted value covers conversion cost with 26% 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 34 out of 100: 51 estimated homes, scored from 0 up to 150.

What the conversion would cost

$405 per square foot all-in across 48,443 sq ft of converted floor, or $19.6M in total — about $385K for each of the 51 homes.

All-in cost per square foot for 81 Post St: base cost plus the code work a change of use triggers.

Base conversion cost	$260/sq ft
Seismic retrofit (change of use)	$45/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	$405/sq ft

That cost is charged across every converted square foot, including the circulation and service area that earns nothing directly. Against it the model sets a completed value of $425K a home, which for 51 homes is $21.7M.

What would have to be true

This one already clears the bar. The question is how much room it has before it stops.

At $425K a home, completed value covers the $19.6M of work with $2.1M to spare. Value per home would have to fall to $385K — 9% below the assumption — before the conversion stopped penciling, or all-in cost would have to rise from $405 to $447 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 81 Post St:

Single-assumption flip points for 81 Post St, each holding the other three at their defaults.

Circulation efficiencythe binding constraint — the least this building would need	21% downto 63%
Completed value per home	24% downto $325K
Average unit size	26% upto 945 sq ft
Conversion cost per square foot	41% upto $366/sq ft

All four are sliders in the survey, where 81 Post St re-scores against your own numbers.

How it compares in Downtown San Jose

81 Post St ranks 12th of the 82 buildings screened here, against a median score of 64.

Its floor plate is better lit than 100% of them, and shallower than 99% of them at its deepest interior point. On size it is the 78th largest by estimated homes. The full survey of all 82 buildings ranks and maps every one of them, and the list by address links each to its own page.

Within the DC zone

10th of 72 zoned DC — the comparison that shares its rules, rents and streets.

72 of the screened buildings are zoned DC. 81 Post St ranks 10th of them against a median score of 61. 31 score 70 or more, their median deepest interior point is 68 ft from a facade against this building’s 30 ft, and together they would hold an estimated 23,276 homes. The group’s top scorer is 1 Almaden Blvd, at 100.

Its nearest match in size: 596 S 2nd St

The screened building closest to 81 Post St in converted floor area is 596 S 2nd St: 58,609 sq ft over 5 stories, against 48,443 sq ft over 9 here.

81 Post St scores 90 to its 82, and with the size held roughly equal most of that lead comes from interior depth: 100 out of 100 here, 76 there (deepest interior point 50 ft from a facade, scored from 80 ft down to 40 ft). On the money they part ways: 596 S 2nd St pencils only with the modeled RESIDE grant, while 81 Post St pencils without a subsidy. The two stand about 3,500 ft apart.

Would it qualify for a RESIDE Act grant?

The model awards 81 Post St $3.1M, 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 06085500800, a 2018 designated Opportunity Zone, which Section 201 lets HUD favor — one of the few statutory priorities this screen can actually check.