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Polk County, IA Accessory Structures: ADU Rules (2026)

Some Restrictions

Compiled from the official code textEditor Martyn O'NeillLast verified September 2026

ADU rules in Polk County, IA, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.

Key Facts

ADUs per property: One maximum
Max size: 1,200 sq ft gross floor area
Owner-occupancy: Required on the property
Floodplain: No ADU in FEMA floodplain
Extra parking: One off-street space required

ADU Eligibility Quick-Check

An Accessory Dwelling Unit (ADU) is a smaller, independent living unit on the same lot as a single-family home: converted garages, detached cottages, basement or attic conversions, and attached additions all qualify. Most states have streamlined ADU permitting since 2020, but local rules still control size, height, and setback.

Is your lot zoned single-family or multi-family residential?
Does your lot have at least 1,200 sq ft of buildable space?
Is your existing home owner-occupied (in most states this is not required, but some require it for ADU permits)?
Will the ADU stay under your state's size cap (commonly 850-1,200 sq ft for detached)?
Can you provide one off-street parking space (waived in many states within 0.5 mi of transit)?

If you answered 'yes' to most of these, you likely qualify in Iowa under recent ADU streamlining laws. The Polk County, IA rules below cover local size, height, and setback requirements.

Summary

Unincorporated Polk County allows one ADU per property, up to 1,200 sq ft and no larger than the principal residence. The owner must live on-site, the ADU meets principal-dwelling setbacks, and none is allowed in a FEMA floodplain.

These county ordinances apply to unincorporated areas of Polk County. Incorporated cities within the county may have their own rules that take precedence over county-level regulations.

A maximum of one (1) accessory dwelling unit may be permitted per property. The gross square footage of the accessory dwelling unit shall not exceed one thousand two hundred (1,200) square feet of gross floor area... Accessory dwelling may not be larger than the existing principal residence.

View official code

Full Breakdown

Article 4, Division 4 of the Zoning Ordinance permits one ADU per lot, attached to or integrated within the primary dwelling or an accessory structure. It may not exceed 1,200 sq ft of gross floor area (excluding garage, porch or deck) and may not be larger than the existing principal residence. It must meet the primary dwelling's setbacks, stay within lot-coverage limits, be architecturally compatible, and provide one added off-street parking space. The owner must reside on the property and record a deed restriction. Single-wide mobile homes, RVs, travel trailers and portable tiny homes are prohibited as ADUs, and no ADU is allowed in a FEMA-mapped floodplain.

Violations & Fines

Zoning violations are enforced by Polk County Planning & Development; unpermitted ADUs may be ordered removed or restored to accessory/single-family use per the required deed restriction.

Frequently Asked Questions

Can I use a tiny home or RV as an ADU?

No. The ordinance bars single-wide mobile homes, travel trailers, RVs and portable tiny homes from being used as an accessory dwelling unit.

Do I have to live on the property?

Yes. Either the primary dwelling or the ADU must be the owner's legal residence, and a deed restriction recording that requirement is required.

Sources & Official References

Other rules in Polk County

Shed & Carport RulesSome Restrictions ADU Owner OccupancySome Restrictions ADU Rental RestrictionsSome Restrictions Tiny HomesHeavy Restrictions Animal Ordinances: Veterinary Clinic ZoningSome Restrictions Landscaping Rules: Tree Removal & Heritage TreesSome Restrictions Landscaping Rules: CompostingLight Restrictions Business Licensing & Operations: Massage EstablishmentsSignificant Restrictions Home Business: Customer Traffic RestrictionsSome Restrictions Business Licensing & Operations: Auto Repair on Residential PropertySignificant Restrictions

All Polk County rules

How Polk County compares: Easiest Cities to Build an ADU·Compare Polk County to another location·View the Iowa accessory structures overview

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ADU Rules in Cities Across Polk County

Des Moines, IA