Run the arithmetic before the next ARC meeting

Take a 2,400-square-foot house with an attached 600-square-foot garage and a 200-square-foot unheated porch. Under the 2025 law, an association or a permitting office working from a figure that included the garage and porch might have measured against 3,200 and reached a 50% allowance of 1,600 — above the 1,000-foot floor, so the larger number governs.

Under SF 2369, “size” is gross living area excluding garages, decks and unheated porches: 2,400. Fifty per cent is 1,200. Still above the floor, so 1,200 governs — a 400-foot reduction produced by nothing but the definition.

The floor does real work at the other end of the range. A 1,600-square-foot house yields a 50% figure of 800, below 1,000, so the statutory 1,000 square feet applies. Below roughly 2,000 square feet of gross living area, the definitional change has no effect at all, because the floor is already controlling. It bites in the middle and upper range — exactly the housing stock most Iowa covenanted subdivisions consist of.

A board reviewing an ADU application should therefore be measuring against gross living area, not against whatever total appears on the assessor's card, which commonly includes attached garage area.

The unfinished-basement asymmetry

Note that the two exclusions do different jobs and point in opposite directions. Excluding unfinished basements from the ADU's measurement is permissive — it lets a bigger structure qualify, since the unfinished portion is not counted against the cap. Excluding garages and porches from the house's size is restrictive, because it lowers the ceiling.

An ADU built over a garage with an unfinished basement below is measured on neither of those spaces. Boards that write their own architectural guidelines around the statutory numbers should mirror both exclusions, or the guideline will diverge from what the city will permit — in whichever direction the guideline was drafted less carefully.

The historic-district commission is a second gate, not a substitute

For associations inside a designated historic district, SF 2369 adds a body whose adverse finding must be written into its own record. That is a meaningful procedural hook: an unrecorded objection is not a finding, and the statute requires the commission to enter it.

It does not displace the association. A historic preservation commission and an architectural review committee are answering different questions under different instruments, and a favourable finding from the commission says nothing about the covenants. The reverse holds too — an association that approves an ADU has not cleared the historic district. Boards in these overlapping jurisdictions should say so explicitly in their approval letters, because owners reliably read one approval as covering both.

What to watch next

Two sessions in a row have produced ADU legislation, and the 2026 bill was corrective rather than expansive — the legislature narrowing its own mandate at the margins after seeing it operate for a year. The carve-out survived both passes untouched, which is the durable finding here.

The measure to watch is production. If Iowa's ADU counts stay flat, the natural next question is what is still blocking them, and private covenants are a conspicuous answer in a state that has twice written them into the exception clause.