2026-09-10 · Iowa · Legislation

Iowa spent 2026 fixing the arithmetic in its accessory-dwelling-unit mandate. Senate File 2369 makes four corrections to the 2025 law, and the one architectural review committees will feel is the smallest: what counts as the “size” of the house an ADU is measured against. Signed April 9, 2026, effective July 1, 2026.¹

It passed 44-0 in the Senate and 85-1 in the House.

The four corrections

One: the mandate is zoned. It now applies only “within a zoning district where a single family residence is an allowed principal use.” That closes a reading under which an ADU had to be permitted on any lot anywhere in the jurisdiction.²

Two: unfinished basements are out of the ADU's own measurement. The 1,000-square-foot / 50% ceiling “shall exclude unfinished basements.”

Three — and this is the consequential one: “size” now has a definition. “‘Size’ means the gross living area of the primary dwelling unit excluding garages, decks, and unheated porches.” The 50% allowance is a fraction, and this shrinks its denominator.

Four: historic districts get a gatekeeper. For a county, an ADU in a historic preservation district under § 15.445 may be regulated only if the historic preservation commission finds and enters into its records that the ADU “would be incongruous with the historical, architectural, archaeological, or cultural aspects of the district.” The city version runs through § 15.459 and “area of historical significance.”

What did not change

The deed-restriction and common-interest-community carve-out is re-enacted word for word, as is the sentence barring a local government from regulating ADUs more restrictively inside a common-interest community than outside one. An Iowa association's authority over accessory dwellings is exactly what it was on June 30, 2026.

1. SF 2369 bill history, Iowa General Assembly (2026 Iowa Acts ch. 1013) ↩
2. SF 2369, enrolled text (PDF), Iowa General Assembly ↩
3. Iowa Code ch. 331 — § 331.301(29) as codified (county home rule, ADU regulation) ↩