20 California St
20 California St is a 7-story building in Downtown San Francisco with 100% of its floor area within daylight reach of a facade. This screen estimates 58 homes and scores it 91 out of 100 for office-to-residential conversion suitability.
CA-11 · Screened 2026-10-12 · Strong candidate
No address point in San Francisco’s records falls inside this footprint, so it is named by the closest one that no other screened building claims — usually a site entrance, but check the outline on the plan below before relying on the street number.
Where 20 California St is
Its block in Downtown San Francisco, drawn from San Francisco's own building outlines and street centerlines.
- Already housing
- Not screened
- 20 California St
This building does not pencil on its own, but a modeled RESIDE Act grant would close the gap if the building qualified for one.
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 20 California St, 2026-10-12.
| Suitability scoreStrong candidate | 91 / 100 |
|---|---|
| Storiesfrom 83 ft LiDAR (2010) height ÷ 12 ft floor-to-floor | 7 |
| Floor plateper floor, from the city footprint | 9,212 sq ft |
| Daylight efficiencyshare within 35 ft of a facade | 100% |
| Deepest interior pointviability threshold is 80 ft | 22 ft |
| Windowless coreper floor — renovated but never rentable | 0 sq ft |
| Estimated homesat 750 sq ft average | 58 |
| Conversion cost$405/sq ft all-in on 55,275 sq ft | $22.4M |
| Gap before grantshortfall against completed value | $1.2M |
| Modeled RESIDE grantbelow the statutory cap | $3.5M |
| BuiltSan Francisco's own record of the construction year | 1908 |
| ZoningFinancial District/South Beach | C-3-O |
| Opportunity Zonenot in a 2018 designated tract | No |
The plan: window line, shape and floor rhythm
62 ft of exterior wall for each home the screen estimates — enough for two- and three-bedroom homes across the plan.
The typical floor has 603 ft of exterior wall, and across 6 residential floors the building carries 3,616 ft of it in total, divided among the 58 homes this screen estimates.
Its plate is elongated at 0.32: a slab or an L, which is why so much of the floor lies within reach of a window: the outline buys daylight that a square plan of the same area would not. How window line and plate shape are measured.
At the model’s 750 sq ft average, the plan works out at about 9.7 homes per floor, repeated on every residential floor, since this building's outline does not change as it rises.
Why 20 California St scores 91 out of 100
Daylight efficiency 100, Interior depth 100, Scale 39, Finance 100 — each out of 100, then weighted.
Score components for 20 California 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 22 ft from a facade, scored from 80 ft down to 40 ft | 100 | 25% | 25.0 |
| Scale58 estimated homes, scored from 0 up to 150 | 39 | 15% | 5.8 |
| Financecompleted value covers conversion cost with 10% 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 39 out of 100: 58 estimated homes, scored from 0 up to 150.
Built in 1908
San Francisco 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 100% daylight figure above deserves.
What the conversion would cost
$405 per square foot all-in across 55,275 sq ft of converted floor, or $22.4M in total — about $386K for each of the 58 homes.
All-in cost per square foot for 20 California 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 $366K a home, which for 58 homes is $21.2M.
What would have to be true
A $1.2M gap before any grant, which the modeled $3.5M closes. What would reopen it soonest: circulation efficiency 10% down.
The shortfall before any grant is $1.2M. Closing it from the value side means each of the 58 homes finishing at $386K rather than the $366K the model assumes — 5% more. Closing it from the cost side means getting all-in cost down from $405 to $384 per square foot.
A modeled RESIDE grant of $3.5M moves that threshold to $326K a home. That is below the assumed value, which is why this building counts as unlocked by the grant — subject to it qualifying under the law's vacant-and-abandoned test, which this data cannot show.
Each of these, moved on its own, would be enough to undo that for 20 California St:
Single-assumption flip points for 20 California St, each holding the other three at their defaults.
| Circulation efficiencythe binding constraint — the least this building would need | 10% downto 72% |
|---|---|
| Completed value per home | 11% downto $326K |
| Average unit size | 11% upto 834 sq ft |
| Conversion cost per square foot | 16% upto $302/sq ft |
All four are sliders in the survey, where 20 California St re-scores against your own numbers.
How it compares in Downtown San Francisco
20 California St ranks 61st of the 205 buildings screened here, against a median score of 87.
Its floor plate is better lit than 100% of them, and shallower than 98% of them at its deepest interior point. On size it is the 165th largest by estimated homes. The full survey of all 205 buildings ranks and maps every one of them, and the list by address links each to its own page.
Within Financial District/South Beach and the C-3-O zone
51st of 165 in Financial District/South Beach, 35th of 88 zoned C-3-O — the comparison that shares its rules, rents and streets.
San Francisco places 165 of the screened buildings in Financial District/South Beach. 20 California St ranks 51st of them against a median score of 88. 121 score 70 or more, their median deepest interior point is 47 ft from a facade against this building’s 22 ft, and together they would hold an estimated 40,456 homes. The group’s top scorer is 870 Market St, at 100.
88 of the screened buildings are zoned C-3-O. 20 California St ranks 35th of them against a median score of 89. 76 score 70 or more, their median deepest interior point is 44 ft from a facade against this building’s 22 ft, and together they would hold an estimated 21,444 homes. The group’s top scorer is 266 Bush St, at 100.
Its nearest match in size: 1017 Market St
The screened building closest to 20 California St in converted floor area is 1017 Market St: 55,115 sq ft over 6 stories, against 55,275 sq ft over 7 here.
The two land within a few points of each other — 91 here, 91 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 only with the modeled RESIDE grant. The two stand about 5,900 ft apart.
Would it qualify for a RESIDE Act grant?
The model awards 20 California St $3.5M, 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 California St
The 4 closest the screen also covers, from 140 ft away. They are the colored outlines on the plan at the top of this page.
- 50 California St37 stories · 73% daylit · 704 estimated homes · scores 61/100 (Worth a feasibility study)about 140 ft away
- 1 California St32 stories · 75% daylit · 477 estimated homes · scores 62/100 (Worth a feasibility study)about 250 ft away
- 201 Sacramento St13 stories · 90% daylit · 217 estimated homes · scores 99/100 (Strong candidate)about 290 ft away
- 150 California St23 stories · 96% daylit · 336 estimated homes · scores 99/100 (Strong candidate)about 440 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.