Zoning › State preemptions › Iowa

Iowa SF 592 (2025) — Statewide Accessory Dwelling Unit By-Right Mandate (IA)

Tracked preemption from the Iowa overlay bundle.

Overview

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Effective
2025-07-01
Sunset
—
Authority
state
Scope
state:IA
Other Iowa preemptions
Iowa Code §414.1(2) — Short-Term Rental Preemption (Residential Use Classification)Iowa Code §459.310 — Master Matrix CAFO Siting ScorecardIowa Code Ch. 161D — Loess Hills Development and Conservation Authority + AllianceIowa Code §414.28 / §335.30 — Manufactured Home Zoning Parity MandateIowa Code Ch. 303 — State Historical Society / SHPO Review + Local Historic Preservation CommissionsIowa Code §352.6 — Agricultural Area Designation + Right-to-Farm Nuisance ProtectionIowa Code Ch. 455B + 567 IAC 71 — Floodplain Development Approval (DNR Flood Plain Program)Iowa Code Ch. 461A + 571 IAC 13 — Sovereign Lands Construction Permits
Primary-source summary
**Last reviewed**: April 2026 **Activity level**: **Moderate** — Iowa is a strong **Home Rule** state (Iowa Const. Art. III §§38A, 39A), but recent sessions have produced discrete statewide preemptions on **short-term rentals** (2020, HF 2641 → Iowa Code §414.1(2)), **manufactured homes** (Iowa Code §414.28, §335.30), and most recently **accessory dwelling units** (2025, SF 592). The long-standing **agricultural exemption** (§335.2 / §414.1A) is the marquee statewide carveout — counties cannot zone farmland or farm buildings, producing well-known friction at the edges of metro areas (Polk,…

Trigger predicate

When this evaluates true for a parcel, the law's preempted fields take precedence over base zoning.

AND
  • parcel.has_single_family_residence == True
  • NOT
    • parcel.carveout_flags ∈ {state_historic_building_code_restricted, deed_restriction_excludes_adu, hoa_common_interest_community_excludes_adu}

Preempted fields

4 fields on the base district schema are rewritten when the trigger fires.

FieldOpValueNote
base_districts[category=res_sf].allowed_usesaddaccessory_dwelling_unitCity AND county SHALL allow a minimum of one ADU on the same lot as a single-family residence — attached or detached. First Iowa statute to mandate a new by-right residential use statewide.
base_districts[category=res_sf].adu_size_capfloor_atmax(1000_sf, 50pct_of_principal)ADU shall not exceed the GREATER of 1,000 sf OR 50% of the size of the single-family residence.
review_typewaive_discretionary—Statute overrides local rules on ADU design, permitting, and occupancy. Cities/counties retain authority over general parking standards but cannot 'make infeasible' the ADU mandate.
utilities.adu_separate_meterpermitshared_lines_with_separate_billing_meterADU may share utility lines with the principal dwelling IF a separate metering system for billing can be provided.

Citation

Authority source
2025 Iowa Acts, SF 592 (91st GA), signed by Gov. Reynolds; codified into Iowa Code ch. 414 (cities) and ch. 335 (counties).
§ SF 592 §§1–4; conformed by Iowa Code chs. 414 and 335 amendments
https://www.legis.iowa.gov/docs/publications/LGE/91/attachments/SF592.html?layout=false

Research notes

Use-class preemption with narrow carveouts. As of 2026-05-18, no narrowing or repeal bills advanced in the 91st GA second session. Open questions: owner-occupancy (statute is silent — some cities still impose owner-occupancy and the question is unsettled), parking ratios, and STR use of ADUs (interplay with §414.1(2)). Cities that have not conformed their zoning ordinances by 2025-07-01 are in facial non-compliance and the state mandate overrides.