Iowa ADU Guide · Des Moines metro
Everything you need to know about building an ADU in Iowa.
A plain-English guide to the 2025 law, the size rules, permitting in Des Moines, what it costs, and what it can return — written for homeowners and investors in the Des Moines metro.
The short version
- You can build one. Iowa's 2025 law (SF 592) requires every city and county to allow at least one ADU on a single-family lot.
- Size: up to 1,000 sq ft or half your home's size — whichever is larger.
- Investors welcome. No owner-occupancy rule — you don't have to live on-site to rent it out.
- By right. A compliant application is approved without a special hearing, on the same timeline as a house.
In this guide
What is an ADU?
An accessory dwelling unit is a second, self-contained home on the same lot as a single-family house. Not a finished basement or a spare room — a complete living space with its own kitchen, bathroom, sleeping area, and usually its own entrance.
It can take several forms: a backyard cottage, a unit above a detached garage, a garage or basement conversion, or an addition attached to the main house. People build them for rental income, aging parents, adult kids, guests, a home office, or a pool house.
The 2025 law that changed everything
For years, whether you could build an ADU in Iowa came down to your ZIP code — some cities allowed them in limited areas, others effectively banned them. Then the state stepped in. Senate File 592, signed in May 2025 and effective July 1, 2025, requires every Iowa city and county to allow at least one ADU on a single-family lot, and it removes the local rules that used to make them impractical.
Cities and counties can no longer:
- Require owner-occupancy. You don't have to live in the main house or the ADU — the change that opens the door for investors.
- Require a relationship between households, or limit occupancy by age or income.
- Force design-matching — the ADU doesn't have to match the main home's exterior, roof pitch, or materials.
- Impose tougher setbacks, height, or lot rules than they apply to the house itself.
- Demand extra parking beyond what the house needs, or charge a special ADU impact fee.
And approvals now work in your favor: a complete, compliant application must be approved without a discretionary hearing, on the same timeline as a single-family home. If a city denies it, it has to say so in writing and tell you how to fix it.
How big can your ADU be?
This is the part people get backwards. Your ADU can be as large as 1,000 sq ft or half your home's size — whichever is larger. The 1,000 is a floor, not a ceiling:
Building an ADU in Des Moines & Polk County
Des Moines is actually one of the friendlier metros in the country for this. The city updated its zoning back in 2019 to allow ADUs (it calls them Accessory Household Units) in most residential zones, charges no impact fees with modest plan-review costs, and generally asks for about one parking space per unit. The city's older ordinance capped detached units around 900 sq ft; the state's 1,000-or-half floor now sets the minimum the city must allow, so confirm the current number before you design.
A few local things still apply and are worth checking per property:
- Historic districts. In areas like Sherman Hill, exterior work needs a Certificate of Appropriateness before a permit.
- Flood zones. Lots along the Des Moines and Raccoon River corridors may need flood insurance and elevated construction.
- Unincorporated Polk County. On rural parcels, septic and well capacity often decide whether a detached ADU — and how many bedrooms — is feasible.
- Building code. Every ADU needs a permanent foundation, proper egress, insulation, and licensed electrical and plumbing. A manufactured or mobile unit used as an ADU must sit on a permanent foundation and be taxed as real property.
What it costs, and what it can return
Costs and returns vary with the build type. As a rule, the cheaper the build, the better it returns — conversions cash-flow hardest, while premium detached units lean toward appreciation. These are planning ranges from 2026 Des Moines-metro figures, not quotes.
A one-bedroom in the metro rents for roughly $1,000–1,200 a month, and a private, newly built ADU with its own entrance can often do a little better. Want the numbers for your property? Run it through our free return calculator.
Renting it out: long-term vs. Airbnb
Long-term rentals (30+ days) are fully protected by the new law — this is the reliable play, and what your numbers should be built on.
Short-term (Airbnb, under 30 days) is a separate story.
The state law protects residential rentals, not short-term lodging. To run an ADU as an Airbnb in Des Moines you'll also need a short-term-rental certificate and Board of Adjustment approval, and you'll face a rule barring a new short-term rental within 700 feet of another licensed one — plus generally only one per detached structure, $500k liability insurance, and the hotel/motel tax. Treat it as upside where the permit and location allow, not as your base case.
One thing the law doesn't cover
A standalone tiny home — one on its own lot with no primary house — isn't an ADU, so none of these protections apply to it. It's judged as a regular single-family home and has to meet the city's minimum dwelling size, which in Des Moines (commonly cited around 1,100 sq ft) rules out most tiny homes. Homes on wheels are treated as RVs and generally can't be a full-time residence outside an RV park. Standalone tiny living is realistic mainly on rural or unincorporated land.
Frequently asked questions
Do I have to live on the property to rent out an ADU?
No. Iowa's 2025 law removed owner-occupancy requirements, so a non-owner investor can build an ADU and rent it out by right.
How big can my ADU be?
The greater of 1,000 sq ft or half your primary home's size. So a 3,000 sq ft home allows up to a 1,500 sq ft ADU, while a smaller home still gets a full 1,000.
Can I put it on Airbnb?
Long-term renting is by-right. Short-term (under 30 days) requires a separate Des Moines permit and Board of Adjustment approval, and can be blocked by the 700-foot density rule — so it's possible but conditional.
How much does an ADU cost in Iowa?
Roughly $60–95k for a garage or basement conversion, $110–150k for a compact detached unit, and $160–190k for a premium detached build — before site-specific factors.
Do the utilities have to be separate?
The ADU can share utility lines with the main home as long as a separate meter for billing can be provided; a city can only require new lines if separate metering isn't otherwise possible.
Can I build a standalone tiny home on an empty lot?
Not as an ADU — that requires an existing home on the lot. On its own, a tiny home must meet the city's minimum dwelling size, which rules most out in Des Moines. It's a rural or unincorporated conversation.
See what your property could do.
Run your lot through our free return calculator, or tell us about the property and we'll send a written estimate and match you with Iowa builders. We handle design, permitting, and construction.
This guide is a plain-language summary based on Iowa Senate File 592 (signed May 1, 2025) and current City of Des Moines and Polk County requirements. It is general information, not legal advice; ADU rules vary by lot and are still being updated to match the new state law. Confirm the specifics for your property with the Des Moines Permit and Development Center (515-283-4200) or your city's planning office before you build.