Premise
The public conversation about historic preservation in Los Angeles operates without parcel-level data. defenders argue HCM status protects irreplaceable architecture; critics argue it blocks housing in transit-rich areas; both sides cite aggregate counts. this study tests the question one parcel at a time. for each of the 1295 active HCMs, six axes are scored from public open data and the designation is classified as load-bearing, blocking redevelopment, redundant, failing protection, insufficient-data, or exempt. the insufficient-data bucket is the residual — what falls out when the public signals are too weak to land anywhere stronger.
Six-axis rubric
A: probability the structure would survive market forces without designation (low = needs protection). B: tourist and cultural currency (Wikipedia pageviews, walking-tour inclusion, public reviews). C: subsidy efficiency (Mills Act, federal historic tax credit, contract value vs preservation outcome). D: externality load (code complaints, 311 CSR cases, encampment / dumping / graffiti, vacancy duration). E: neighborhood health (median household income, distress indicators). F: alternative-use value (parcel acres, TOC tier, TPA eligibility, zoning capacity).
Necessity classifier
After the six axes, a rule-based classifier reads scores plus typology plus Mills Act contract data plus AECOM equity tier and assigns one of seven verdicts. load-bearing means an active Mills Act contract on a property whose owner is in a medium-to-high or high barriers equity tier — the subsidy is plausibly funding upkeep the owner could not otherwise sustain. subsidy-not-load-bearing means an active Mills Act contract on a property in the low or low-to-medium barriers tier — the city is paying, but the owner is in a high-resource neighborhood and likely would have maintained the property without the subsidy. blocking-redevelopment means the HCM is preventing higher-value use without protecting the structure. redundant means the building would survive without the designation through private value or alternative protections. failing-protection means the HCM exists but vacancy and deterioration continue. insufficient-data means none of the above conditions matched because the public signals are too weak — not a finding that the designation is ornamental, just an honest admission that the rubric cannot see what (if anything) it is doing. exempt covers religious, federal, or excluded categories.
Findings
99 Of 1295 active HCMs (7.6 percent) classify as load-bearing — active Mills Act contract on a property in the medium-to-high or high barriers equity tier, where the subsidy is plausibly funding upkeep the owner could not otherwise sustain. 223 (17.2 percent) carry an active contract but sit in the low or low-to-medium barriers tier — the city is paying, but the owner is in a high-resource neighborhood and would likely have maintained the property without the subsidy. 819 (63 percent) sit in insufficient-data — no Mills Act and no other strong signal. 86 as redundant. 2 as blocking redevelopment. 66 as exempt. across all 322 mills-act-carrying HCMs, approximately $20 million in annual owner property-tax savings, $2.18 million of which is la city revenue loss. 82.6 percent of those savings flow to the low or low-to-medium barriers tiers — the 223 subsidy-not-load-bearing properties. 26 condominium contracts alone account for 33 percent of total savings. 659 single-family contracts account for 25 percent. that distribution is the substantive finding the city's own program assessment surfaced and the per-property data confirms at the parcel level.
Vacancy inference fix — 2026-05-11
The first run produced 4 blocking-redevelopment and 8 failing-protection verdicts. on review the rule that inferred vacancy from "no permit data + 1 open CSR case" was firing on actively-used commercial parcels and quiet single-family residences. magic castle (active members club) and arthur s. bent house (likely occupied sfr) were both incorrectly flagged. the rule was tightened in scripts/HCM-1200/lib/vacancy.mjs with 13 tests covering the previously-failing cases. all 1295 HCMs were rescored; 10 necessity verdicts changed (9 vacant→null, 1 partial), all moving from vacant verdicts to the residual bucket. the two remaining blocking-redevelopment cases (HCM-587 lincoln heights jail, HCM-790 belmont tunnel) survive on strong independent vacancy evidence (12 and 8 code complaints respectively, plus manual override for 790).
Verdict-label fix — 2026-05-11
The residual bucket was originally labeled "symbolic" — which implied the rubric had affirmatively determined the designation was functioning as recognition only. it had not. the bucket is whatever falls out when none of the other four conditions match. for most properties that means the public signals were too weak for the rubric to classify, not that the designation is provably ornamental. the label has been renamed insufficient-data so the audit stops overclaiming on the residual.
Mills Act data integration — 2026-05-12
Melissa jones (la office of historic resources) replied to the may 11 data request the following morning, pointing to appendix a of the 2022 program assessment. the appendix contains 931 Mills Act contracts active in 2019 with per-property fields: address, APN, HCM number where applicable, ma contract number, 2019 enrolled value, trended value, owner savings, city unrealized revenue, equity index score, and equity index category. extracted from the pdf via scripts/HCM-1200/extract_mills_act_pdf.py using pdfplumber. the new matcher in scripts/HCM-1200/lib/fetchers/mills_act_appendix.mjs indexes by HCM number (348 records) and APN (979 records) and resolves the c-axis directly. all 1295 HCMs were rescored. 322 HCMs matched to active contracts. the CPRA fallback queued for may 18 is cancelled.
Load-bearing definition fix — 2026-05-12
The first pass at the mills-act-integrated rubric classified all 322 HCMs with a Mills Act contract as load-bearing — i.e. treated the existence of a contract as evidence the subsidy was doing real work. that was the same overclaiming pattern as the original "symbolic" label. a $69 annual savings on a $5 million carthay circle home is not load-bearing; the owner would have maintained the property regardless. the fix splits load-bearing by AECOM equity tier per the city's own equity analysis framework: contracts in medium-to-high or high barriers (where savings plausibly matter to the owner's ability to maintain the property) stay load-bearing; contracts in low or low-to-medium barriers move to subsidy-not-load-bearing. after the split: 99 load-bearing, 223 subsidy-not-load-bearing. 69 percent of what the first pass called load-bearing was actually a subsidy flowing to a property the owner would have maintained without it. the 223 subsidy-not-load-bearing HCMs are the parcel-level version of the "subsidies for the already saved" critique.
Vacancy-detection limit — 2026-05-12
Only 2 HCMs are classified as blocking-redevelopment (HCM-587 lincoln heights jail, HCM-790 belmont tunnel). that count is the rubric's lower bound, not a definitive total of vacant transit-rich historic parcels in la. vacancy is inferred conservatively from LADBS permit history + 311 CSR cases + code complaints — the strict rule was tightened on 2026-05-11 to require corroborating signals after the magic castle false positive. an integration test suite now locks the count in place: it must not drop below 2 (HCM-587 and HCM-790 are manually validated), must not exceed 5 without an explicit methodology update, and must not include magic castle or bent house. there are almost certainly more vacant historic buildings in la than 2; the rubric cannot detect them from public open-data signals. la dbs maintains a vacant building maintenance registration list under LAMC 91.8904.1, but it is not currently exposed as a spatial open-data dataset. that list is the next data target. property tax delinquency from the county assessor and machine-vision aerial imagery analysis are alternative paths.
Two types of vacant HCM — 2026-05-12
Vacant HCMs in la fall into two qualitatively different categories. type 1: commercial / industrial / civic obsolescence + contamination overhang — obsolete infrastructure on parcels carrying decades of soil contamination from prior uses. both currently-detected blocking-redevelopment cases (HCM-587 lincoln heights jail, HCM-790 belmont tunnel) are type 1. policy response: adaptive reuse paired with environmental cleanup, not delisting. type 2: private residences with structural damage trapped by HCM-related laws — buildings physically unable to be occupied (fire, earthquake, foundation failure) where cultural heritage commission demolition review and Mills Act / HPOZ alteration covenants prevent the owner from demolishing or substantially altering. policy response: structural-distress accelerated demolition pathway (with photo-documentation as the preservation outcome) or expanded restoration subsidy. the current rubric collapses both into one "vacant" label and cannot distinguish them without integrating DTSC contamination data (EnviroStor + cortese) for type 1 and la dbs substandard / unsafe building registry (LAMC 91.8902) for type 2. zero type-2 cases are currently detected — not because none exist, but because the data feed does not.
We do not have occupancy data — 2026-05-12
The field labeled "vacancy" or "vacancy_status" throughout this audit is a permit-activity proxy, not a measurement of occupancy. across 1295 active HCMs the proxy breaks down by basis: 548 "active" came from $250k+ in recent construction investment (strongest activity signal in the rubric); 479 "active" came from a single permit in the last 5 years (weak signal); 51 "partial" came from a single permit 5-10 years old; 80 "unoccupiable" came from typology (signs, tunnel portals, public art); 2 "vacant" came from no-permits + high complaints or manual override; 10 from probe-set manual overrides; 127 "unknown" came from no signal at all. none of these prove occupancy. an institutional owner doing deferred maintenance, a developer pulling pre-demolition permits, or a vacant property being prepared for sale will all register as "active." conversely, an occupied owner-occupied property that hasn't pulled a permit in 5 years will register as "unknown" or "partial." each per-HCM detail page now carries a "vacancy proxy basis" field naming the specific rule that fired. real occupancy data would require integrating la dbs vacant building registration (LAMC 91.8904.1), LADWP service status, USPS undeliverable-as-addressed rates, county assessor property tax delinquency, or aerial imagery + ml classification. none of those are currently in the rubric. this is the largest known structural limitation of the audit.
What this is not
Not a delisting list. not a model of what to demolish. the insufficient-data bucket is the rubric admitting it cannot see what the designation is doing — not a verdict that the designation is doing nothing. the redundant cases describe properties where the market or alternative protection is sufficient on its own. the blocking-redevelopment cases are sites worth field-validating, particularly vacant or chronically-distressed parcels in transit-rich areas where the designation is preventing redevelopment without protecting the structure.
Sources
La hub arcgis historic-cultural monuments feature service (registry with polygons and designation dates), la city open data permits (d9aa-v8bm), customer service requests (bsvt-chkv), 311 (h65r-yf5i), us census ACS vintage acs2023_current, Wikipedia pageviews api, anthropic claude sonnet for typology classification, Mills Act assessment program report (2022) and amendments deck (2025). per-property Mills Act contract list requested from office of historic resources may 11 2026.
Explorer
The interactive explorer at /HCM-1200 lets you filter and sort the full 1295-entry register by flag, necessity, typology, and per-axis score. each row links to a per-HCM detail page with the radar chart, fetched data table, narrative, and polygon footprint.