Ames homeowners can now build accessory dwelling units thanks to new city ordinance

Homeowners can now build secondary units up to 900 square feet thanks to a new city ordinance passed during Tuesday's Ames City Council meeting.

The ordinance restricts accessory dwelling units (ADUs) to one bedroom and a maximum of 900 square feet, while the code also requires a single parking spot. The ordinance would also require a paved driveway and a sidewalk connected to the parking space. The property owner must reside in either the primary home or the ADU, allowing one unit on the property to be rented.

The council first proposed the new ADU ordinance in the final quarter of 2023.

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What is an accessory dwelling unit?

The City of Ames hopes the ordinance will “expand housing opportunities” and “diversify housing choices."

ADUs are additional residential buildings occupying the same lot as a primary single-family but with a bedroom, kitchen and bathroom. They are also called second units, granny flats, or mother-in-law units.

The old code currently didn't allow for such a structure to exist.

The units cannot be bought or sold separately, though they are often used to provide additional income through rent or to house a family member.

"There is a national interest in having more housing choices as costs increase," the City of Ames said in a statement on its website. "The City is exploring more housing choices within existing neighborhoods that complement the surroundings. This was a goal outlined in Ames Plan 2040 that improves choice, sustainability, and vitality."

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What qualifies as an ADU?

ADUs must also be owner-occupied. The secondary unit cannot be registered as a rental if the owner is not living on the property.

"That is the commitment we made earlier in the process," Ames Planning and Housing Director Kelly Diekman said at the Dec. 12 city council meeting. "Not only do you have to be the owner to get the building permit, but you have to be an owner on-site if you are ever to register the property for rental purposes."

Diekmann said an Airbnb would be classified as a "home share." He said the primary residence could still be used as a home share if the ADU is licensed as a rental.

A home share must be the primary residence, and it can be used for up to 90 days a year. Diekmann said residence should not be confused with presence, meaning the owner does not have to physically be at the property for all 90 days.

ADUs will not be allowed in the front yard of residential property, instead restricted to the "rear" yard with specific regulations, with the entire structure and parking space or driveway not to exceed 25 percent of the yard.

The city considers the rear yard as "the entire area between the primary dwelling and the rear property line, not just the rear setback area."

A sidewalk would be required to connect the primary exterior entrance of the accessory dwelling with the paved parking area.

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Other notable requirements of the proposed ADU code

(According to the City of Ames):

Parking - One off-street parking space would be required for the accessory dwelling in addition to thetwo spaces required for the principal building. Although spaces for the principal building caninclude two cars parked in tandem, an ADU parking space cannot be in front of or behindanother required parking space. All parking spaces must be paved. Paving in the front yard isnot permitted per 29.406 of the Zoning Ordinance.

Bedroom - The accessory dwelling may only have one bedroom. Any area separated fromthe one bedroom, living area, kitchen, and bathroom that exceeds 70 square feet will becounted as a bedroom per the definitions of the Zoning Ordinance.

Driveway - A paved driveway would also be required. For lots accessible from an alley, any new drivewayshall be constructed in the rear yard with access only from the alley. The driveway leading froman alley to the entrance of a garage shall be either 8 feet from the property line abutting thealley or a minimum of 20 feet from the property line abutting the alley.

Rentals - Only one of the two units may be a rental. Any ADU or principal building that isintended for use as a rental must be registered with the city and have a valid rental permit. Allrequirements of the Rental Code (Chapter 13) apply.

Celia Brocker is a government, crime, political and education reporter for the Ames Tribune. She can be reached at CBrocker@gannett.com.

This article originally appeared on Ames Tribune: Ames council approves ordinance for secondary units