ADU Atlas

About & method

Open data for a debate that usually runs on opinion

What this is

The ADU Potential Atlas estimates how many single-family lots in Greater Cleveland could hold an accessory dwelling unit (a small second home on the same lot) under the rules in effect today, under proposed rules, and under a hypothetical reform. It covers 10 cities: Cleveland Heights, Lakewood, Cleveland, Shaker Heights, Parma, University Heights, South Euclid, Garfield Heights, Euclid, Fairview Park.

It is for residents, council members, planning staff and reporters who want to talk about ADUs with the same facts in front of them: how many lots have room, where they are, what a rule would actually allow, and how much housing that might realistically mean. It does not take a side.

How the estimate is built

Three separate questions, answered separately so you can see which one drives a result.

  1. 1. Is there physical room?Using county lot lines and building outlines, the screen finds the yard behind the house, keeps 5 ft from side and rear lot lines, 10 ft from the house and 5 ft from any garage or shed, and tests whether a 20 ft footprint fits in what is left. A lot also counts if it has a detached garage or shed of 240–1,200 sq ft that could be converted. The same settings are used in every city.
  2. 2. Is an ADU allowed?Each lot's zoning district is compared with the districts a set of rules permits. Where the rule for a district has not been verified, or zoning data is uncertain, the lot is reported as unknown: never counted as allowed, never as prohibited.
  3. 3. How many would be built?Nobody knows. The atlas multiplies the lots that are both allowed and have room by an adoption rate you can change, from 0.5% to 10% over 10 years. The default, 2%, reflects what cities that reformed their rules have seen. Growth compares that with the Census count of existing homes.
STREETHOUSEGARAGE20 ftfits5 ft10 ftopenrearyardorconvertLOT · 50 × 140 ft
  • modeled ADUs = round(buildable × uptake_rate); at most one ADU per lot
  • housing growth = modeled_adus / baseline.housing_units × 100; unknown when baseline is null

How well it holds up

A reviewer judged a stratified random sample of single-family lots from aerial imagery, before seeing the screen's answer: is there room behind the house for a ~20 x 20 ft cottage, or a detached garage to convert? Agreement is weighted by each stratum's share of screened lots; lots the screen marks unknown are excluded. 300 of 300 sampled lots were reviewed, and the reviewer agreed with the screen on 95% of lots (95% interval 94%–97%). The review covered 5 of the 10 cities. The others use the same county parcel and building records and the same screen, but have not been checked separately.

Agreement between the screen and the blind review, by city
CityAgreementLots with room: screenReviewer implies
Cleveland Heights98% (97%–99%)12,132≈ 12,482
Lakewood98% (97%–99%)8,738≈ 8,920
Cleveland93% (90%–97%)67,761≈ 74,461
Shaker Heights98% (97%–99%)6,587≈ 6,858
Parma99% (98%–99%)27,019≈ 27,474

The screen errs on the cautious side. When it said a lot had room, the reviewer agreed nearly every time. Most disagreements were lots the screen ruled out that looked usable from above: yards just under the 20 ft test, garages beside rather than behind the house, and patios or decks that county building outlines count as part of the house but that could be removed. So the totals are, if anything, a little low.

Checks the screen against the same kind of evidence it uses (overhead photos and county building outlines, a few years old). It supports neighborhood-scale totals; it does not certify any single lot.

Rules by city

Rules are read from each city's codified ordinances. Every city is marked partial coverage for now: the physical screen is complete, but some zoning details are still being verified against the official code.

Cleveland Heights

Cleveland Heights on the map →

Lakewood

  • Current rules In effectConditional use · Codified Ordinances of Lakewood §1161.03(bb); Ord. 07-2023 · as of 2026-10-13Passed 2023-11-20. Max size the lesser of 50% of the principal footprint or 1,000 sf; owner occupancy (deed restriction); one off-street parking space; not closer to the street than the house. Minimum rental term (60 vs 180 days) unverified.
Lakewood on the map →

Cleveland

Cleveland on the map →

Shaker Heights

  • Current rules In effectNo ADUs · Codified Ordinances of Shaker Heights §1262.01(F), §1260.01(C); re-enacted by Ord. 26-01 · as of 2026-10-13Ord. 26-01 (enacted 2026-02-09, effective 2026-03-11) kept the ban on living quarters in accessory buildings. Single- and two-family districts allow one principal building per lot (§1260.01(C), verified only in a code mirror), so a detached second dwelling is not allowed in TF either. No ADU proposal found; the city's 2027 Housing Plan (RFP 2026-08) is the next opening.
Shaker Heights on the map →

Parma

  • Current rules In effectNo ADUs · Codified Ordinances of Parma §§1153.01–1153.03, §1155, §1121 (lot: one main building) · as of 2026-10-13Read in a code mirror, not yet checked against the official code. The code never mentions accessory dwellings. SF districts are "exclusive single-family residential uses" (§1153.01); a lot is occupied by "one main building" (§1121); a resident family may rent one room with no separate cooking (§1153.03(h)). 2F allows converting houses to two units, apparently within one building. No ADU proposal found.
Parma on the map →

University Heights

  • Current rules In effectNo ADUs · University Heights Zoning Code (1956, as amended): no accessory dwelling provision · as of 2026-10-14The City's 2025-09-30 zoning update presentation lists "Allow ADUs by right" as a proposed change. Not yet confirmed in the official code (AmLegal blocks automated access).
  • Proposed zoning code (May 2026 draft) ProposedBy right · Public review draft zoning code (May 2026), §1222.05(a), Tables 1219.02-1 and 1221.05-1 · as of 2026-10-14One ADU per lot, detached in the rear yard, attached, or above a detached garage; max 1,200 sf beside a one-unit house on a lot of at least 4,800 sf; no taller than the house; owner must live on site; shares the house's utilities. Accessory buildings: 5 ft side and 10 ft rear setback, 22 ft tall, 25% building coverage cap (coverage not yet modeled). Next town hall 2026-11-04.
University Heights on the map →

South Euclid

  • Current rules In effectConditional use · Codified Ordinances of South Euclid §723.03(g) (Ord. 14-23, 2023-12-11; amended Ord. 45-25, 2026-04-27) · as of 2026-10-14Conditional use with Architectural Review Board design review. One ADU per lot, attached or detached, rear yard only (attached may sit in a side yard). Max 500 sf on lots of 7,500 sf or less, 1,000 sf on larger lots; 24 ft or two stories; detached units 5 ft from side and rear lines; at least one off-street space. The owner must live on site, and neither the house nor the ADU may be rented, including short-term. Read in a third-party copy of the code; not yet checked against AmLegal.
South Euclid on the map →

Garfield Heights

  • Current rules In effectBy right · Codified Ordinances of Garfield Heights §1151.11 (Ord. 87-2025, passed 2026-01-12, effective 2026-02-16) · as of 2026-10-14Administrative (staff) approval, no hearing. One ADU per lot beside a one-unit house; max 1,200 sf; accessory-structure height limits; 3 ft from lot lines; not in front of the house; no off-street parking required; no owner-occupancy rule; occupancy up to two adults per bedroom. The lot must meet district minimums: only lot area is modeled here, so lots that are too narrow or shallow are still counted. Read in a third-party copy of the code; not yet checked against AmLegal.
Garfield Heights on the map →

Euclid

  • Current rules In effectPermit path unknown · Codified Ordinances of Euclid Ch. 1352, Table 1352.04 and §1352.07(e) (Ord. 120-2024, passed 2024-10-07) · as of 2026-10-14Euclid's 2024 code update allows a second, stacked unit (two-family house) by right in U1 and U2 but has no accessory dwelling use. One clause about rear dwellings mentions "an accessory dwelling structure" sharing a lot, so a detached ADU's status is unclear; these lots are shown as unknown until Euclid Planning & Development confirms how the code is read. Read in a third-party copy of the code; not yet checked against AmLegal.
Euclid on the map →

Fairview Park

  • Current rules In effectNo ADUs · Codified Ordinances of Fairview Park §1105.06 (accessory living accommodations), Ch. 1117 · as of 2026-10-14The code allows "accessory living accommodations" only without cooking facilities; a unit with a kitchen counts as a separate dwelling unit, which the one-family districts do not permit. Read in a third-party copy of the code; not yet checked against AmLegal. Council reportedly discussed ADUs during a zoning-overhaul discussion on 2025-04-28 (secondary source, unconfirmed).
Fairview Park on the map →

Every city is also shown under a hypothetical by-right reform: ADUs allowed without special approval in every residential district that contains single-family lots. It is a yardstick defined by this atlas, not a proposal any city has made.

Data sources

Adoption rate evidence

Share of buildable lots that add an ADU within 10 years. Observed US rates after reform are roughly 2-3% over a decade (Seattle 2019-2024; lowest-value California neighborhoods), with rare outliers near 8%. This is an assumption, not a forecast.

Limitations

  • Screening results are heuristics, not legal determinations or construction feasibility assessments.
  • Physical screen ignores trees, slopes, driveways and garage access, easements, utilities and floodplains.
  • Coverage caps that include pavement are not modeled; no impervious-surface data is used yet.
  • Corner and through lots (MULTI_FRONTAGE) are lower confidence.
  • Only assessor land-use 5100 (one-family) lots are screened; two-family lots are excluded.
  • Modeled ADUs depend entirely on the uptake assumption and do not predict rents or prices.

Privacy

The atlas never downloads or publishes owner names, mailing addresses or sale prices. Each lot on the map shows only its county parcel number, zoning district, lot size and screening results. The aerial images used to check the screen are not published.

Who made it

Made by NeoDataLabs. The atlas is a NeoDataLabs civic-data project, built to show what open public records can add to local housing discussions. It has no sponsor and no partner organization yet. Universities, housing nonprofits and city planning offices that want to check the rules, extend coverage to more cities or use the data are welcome.

Corrections and questions: info@adupotential.com

Data schema 0.5.0 · analysis spike-0.1 · generated 2026-10-14