HomeMy WebLinkAboutA050 - Hearing on ZTA for Accessory Dwelling Units (ADU)ITEM #:51
DATE:06-09-26
DEPT:P&H
SUBJECT:ACCESSORY DWELLING UNIT STANDARDS ZONING ORDINANCE TEXT
AMENDMENT
COUNCIL ACTION FORM
BACKGROUND:
Earlier this year, the Iowa General Assembly passed Senate File 2369, which makes changes
to the way counties and cities in Iowa can regulate Accessory Dwelling Units (ADUs). The new
bill amends standards approved last year by the state, Senate File 592, which preempted
certain county and city regulations regarding ADUs.
The new bill (SF 2369) was signed into law by Governor Reynolds on April 9, 2026, and
comes into effect on July 1, 2026. The minimum requirements of the new state law
necessitate some changes to the City's local zoning standards. Fundamentally, the legislation
requires municipalities to permit ADUs on single-family lots in manner that is similar to that of a
single-family dwelling.
The 2025 legislation defines an accessory dwelling unit as: “an additional residential dwelling
unit located on the same lot as a single family residence that is either attached to or detached
from the single family residence.” A single-family residence as defined by the state
corresponds to one- and two-family homes as defined in the Ames Zoning Ordinance.
The new law passed by the State legislature this year requires the following changes to
the City's Zoning Ordinance:
Clarifying that municipalities are only required to permit ADUs on properties where
single-family residences are allowed as a principal use. The law in 2025 was unclear as
to whether municipalities were required to allow ADUs on properties with nonconforming
single-family residences.
Adding that an unfinished basement does not count towards size limitations. Last year ’s
law stipulated that an ADU is limited in size to 1,000 square feet or 50% of the size of the
single-family residence, whichever is larger. This year ’s law states that the size
calculation of an ADU shall exclude unfinished basements. Note that finishing out
basement space in the future may not be permissible if the size limit is already met.
Amends the language relating to the review of ADUs on properties designated as historic
(including historic districts). No specific change to Chapter 31 is needed to implement
this requirement; it is consistent with the City's current process.
Defines “the gross living area of the primary dwelling unit excluding garages, decks, and
unheated porches.” Last year ’s law did not explain how size was defined for calculating
the area of an ADU and City relied upon its own zoning definition of gross floor area.
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Staff also has identified two changes to the City's own standards as companion
changes to the mandated State requirements:
Clarifying that in zoning districts where side setbacks are based on the number of
building stories (six feet for one story, eight feet for two story, etc.), side setbacks
for attached ADUs shall match the single-family residence and side setbacks for
detached ADUs shall be considered independent of the setbacks applied to the
house. This means a one-story ADU could have a lesser setback on the same lot
as a two-story principal dwelling or vice versa.
Affirming that ADU standards for side and rear setbacks and lot coverage are
eligible for Alternative Design (the 20% Alternative Design Rule). Staff believes
minor flexibility similar to principal dwellings will help for reasonable construction
of ADUs for smaller lots. The overall size and other main limitations on ADUs are
not affected by this allowance for flexibility.
A draft ordinance for the changes is Attachment A.
Planning & Zoning Commission:
On May 20, 2026, the Planning and Zoning Commission reviewed the proposed changes. The
Commission voted 4-0-0 to recommend that Council approve the changes to the Zoning
Ordinance that includes the both the state requirements and staff-suggested changes.
ALTERNATIVES:
1. Approve the text amendment for Accessory Dwelling Units as shown in Attachment A.
2. Approve the text amendment for Accessory Dwelling Units with language other than
what is shown in Attachment A.
3. Refer the matter back to staff for further consideration.
CITY MANAGER'S RECOMMENDED ACTION:
Staff has prepared a draft ordinance (Attachment A) to comply with the new state
statute for Accessory Dwelling Units, which comes into effect on July 1 of this year.
The revised code amends the regulations in response to state law and makes two
additional changes that staff believe are beneficial. Therefore, it is the recommendation of
the City Manager that the City Council approve Alternative #1 as stated above.
ATTACHMENT(S):
Attachment A - ADU Text Amendment.pdf
Attachment B - Draft ADU Ordinance.pdf
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ATTACHMENT A
Proposed Zoning Text Amendments for
Accessory Dwelling Units
CHAPTER 29, ZONING
* * *
Sec. 29.409. ACCESSORY DWELLING UNIT (ADU) STANDARDS.
An ADU is a newly constructed additional residential dwelling unit located on the same
lot as a single-family residence as defined by state law. This includes properties with a
single-family or two-family dwelling defined within the Zoning Ordinance.
(1) Where Permitted.
(a) An ADU is permitted on any lot:
(i) with only a single-family residence. and
(ii) that is within a zoning district that allows for single-family residence
as a principal use.
(b) Overlay zoning districts. If the property is in an overlay zone, such as the
Single-Family Conservation (O-SFC) or the Historic (O-H), it may be subject
to additional design standards and permitting requirements. In the event of
conflict between overlay regulations and the regulations included herein,
the more restrictive regulations shall control.
(c) An ADU proposed for a lot within a local historic district or on a locally
designated property shall be regulated to the extent that the City or Historic
Preservation Commission determine that the proposed ADU would be
incongruous with the historical, architectural, archaeological, or cultural
aspects of the area, and enters into official records the reasons for such
determination.
(2) Independent Dwelling Unit.
(a) Location. An ADU may be:
(i) Attached to the single-family residence.
(ii) Detached from the single-family residence in a free-standing
structure.
(iii) Located within a converted, existing accessory structure, so long
as the structure complies with all ADU requirements, including
setbacks.
(iv) No ADU may be established within an existing single-family
residence.
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(b) Functions Independently. The ADU must function independently from the
single-family residence. It must include its own bathroom and kitchen
facilities and be connected to public utilities including water and sanitary
sewer. Separate metering is not required but allowed.
(c) Foundation. Whether constructed on site or premanufactured, an ADU must
be placed upon a permanent foundation.
(3) Development Requirements
(a) All ADUs shall follow the same regulations as the single-family residence
on the property regarding:
(i) Maximum height
(ii) Minimum setbacks
(iii) Minimum lot size
(iv) Minimum building frontages
(v) Maximum lot coverages
(vi) Density requirements
(vii) Aesthetic or architectural standards
(b) Setbacks.
(i) Where side setbacks are based on building height, the single -
family residence and the detached ADU shall individually have
minimum setbacks based on their respective heights.
(ii) Setbacks for an attached ADU shall be the same as the single-
family residence to which it is attached.
(c) ADUs are not regulated as accessory structures or accessory buildings in
Sec. 29.408.
(d) ADUs are not subject to the rear yard coverage restrictions in Sec. 29.408.
(e) ADUs may be either freestanding or attached to the single-family residence.
(i) Attached ADUs must be of new construction and not a conversion
of an existing dwelling.
(ii) Conversion of a detached accessory structure to an ADU must be
in compliance with all zoning standards, including setbacks and lot
coverage as a newly constructed ADU. For example, a
nonconforming detached structure cannot be converted if it does
not meet current zoning standards.
(f) The design of the ADU when attached to the home with a total of two doors
facing the street is subject to the design requirements of two-family homes.
(g) ADUs are not required to adhere to the minimum standards of 29.410(1)(a),
relating to minimum dimensions.
(4) Size Limitations and Bedrooms.
(a) The ADU may must not exceed 1,000 square feet or 50% of the size of the
single-family residence, whichever is larger.
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(i) Size means the gross living area of the primary dwelling unit
excluding garages, decks, and unheated porches. For purposes of
this section, size of the single-family residence is calculated on the
Gross Floor Area as defined in Sec. 29.201.
(ii) The size calculation of an accessory dwelling unit shall exclude
unfinished basements. It may therefore be impermissible to finish
and complete an unfinished basement of an ADU if finishing this
space causes the ADU to exceed the size limitation set in Sec.
29.409(4)(a). For purposes of this section, the size of the ADU is
calculated on the Gross Floor Area as defined in Sec. 29.201.
(b) The ADU is limited to one bedroom. Any additional area or room that meets
the definition of a bedroom as defined within the Zoning Ordinance is
prohibited.
(5) Parking & Driveways.
(a) No on-site parking is required for the ADU in addition to the required parking
for the single-family residence. On-site single-family residence parking must
be provided to approve an ADU. If parking is provided, it must be paved and
located in accordance with the requirements of 29.406.
(b) Sidewalk. A sidewalk is required to connect the primary exterior entrance of
the ADU with the parking area, the single-family residence, or the street.
(6) Occupancy.
(a) Occupancy limitations may apply to Near Campus Neighborhoods, as
defined within Chapter 13, Rental Code.
(b) Rentals. Any ADU or single-family residence that is intended for use as a
rental must be registered with the city and have a valid rental permit. All
requirements of Chapter 13, Rental Code apply.
Sec. 29.1502 Site Development Plan Review
* * *
(7) Alternative Design Review.
* * *
(d) Ineligible Standards. The following standards in Chapter 29 of the Municipal Code
are not eligible:
(i) Density (including lot area per unit)
(ii) Location of and paving of vehicle maneuvering areas and driveways in a front
yard
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(iii) Minimum lot frontage
(iv) Rock size limitations in Campustown Service Center Standards
(v) Lighting output standards
(vi) Fence Height Limitations
(vii) Dwelling Design Standards of 29.409 and 29.410 ., with the exception of ADU
standards for side and rear setbacks and lot coverage.
(viii) Building Story Limitations
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ORDINANCE NO. ____
AN ORDINANCE TO AMEND THE MUNICIPAL
CODE OF THE CITY OF AMES, IOWA, BY
AMENDING SECTIONS 29.409 AND 29.1502
THEREOF, FOR THE PURPOSE OF
AMENDING ACCESSORY DWELLING UNIT
(ADU) STANDARDS, REPEALING ANY AND
ALL ORDINANCES OR PARTS OF
ORDINANCES IN CONFLICT TO THE EXTENT
OF SUCH CONFLICT; AND ESTABLISHING
AN EFFECTIVE DATE.
BE IT ENACTED, by the City Council for the City of Ames, Iowa, that:
Section One. The Municipal Code of the City of Ames, Iowa shall be and
the same is hereby amended by amending Sections 29.409 and 29.1502 as
follows:
“Sec. 29.409. ACCESSORY DWELLING UNIT (ADU) STANDARDS.
An ADU is a newly constructed additional residential dwelling unit located on the
same lot as a single-family residence as defined by state law. This includes
properties with a single-family or two-family dwelling defined within the Zoning
Ordinance.
(1) Where Permitted.
(a) An ADU is permitted on any lot:
(i) with only a single-family residence. and
(ii) that is within a zoning district that allows for single-family
residence as a principal use.
* * *
(c) An ADU proposed for a lot within a local historic district or on a
locally designated property shall be regulated to the extent that the
City or Historic Preservation Commission determine that the
proposed ADU would be incongruous with the historical,
architectural, archaeological, or cultural aspects of the area, and
enters into official records the reasons for such determination.
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* * *
(3) Development Requirements.
* * *
(b) Setbacks.
(i) Where side setbacks are based on building height, the
single-family residence and the detached ADU shall
individually have minimum setbacks based on their
respective heights.
(ii) Setbacks for an attached ADU shall be the same as the
single-family residence to which it is attached.
* * *
(4) Size Limitations and Bedrooms.
(a) The ADU may must not exceed 1,000 square feet or 50% of the
size of the single-family residence, whichever is larger.
(i) Size means the gross living area of the primary dwelling unit
excluding garages, decks, and unheated porches. For
purposes of this section, size of the single-family residence
is calculated on the Gross Floor Area as defined in Sec.
29.201.
(ii) The size calculation of an accessory dwelling unit shall
exclude unfinished basements. It may therefore be
impermissible to finish and complete an unfinished
basement of an ADU if finishing this space causes the ADU
to exceed the size limitation set in Sec. 29.409(4)(a). For
purposes of this section, the size of the ADU is calculated on
the Gross Floor Area as defined in Sec. 29.201.
* * *
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Sec. 29.1502 Site Development Plan Review
* * *
(7) Alternative Design Review.
* * * (d) Ineligible Standards. The following standards in Chapter 29 of
the Municipal Code are not eligible:
* * *
(vii) Dwelling Design Standards of 29.409 and 29.410., with the
exception of ADU standards for side and rear setbacks and lot
coverage.
* * * ”
Section Two. All ordinances, or parts of ordinances, in conflict herewith
are hereby repealed to the extent of such conflict, if any.
Section Three. This ordinance shall be in full force and effect from and
after its passage and publication as required by law.
Passed this day of , .
_____________________________ ___________________________
John A. Haila, Mayor
First Reading:
Second Reading:
Third Reading:
Passed on:
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I, Renee Hall, City Clerk of the City of Ames, Iowa, hereby certify
that the above and foregoing is a true copy of Ordinance No. ______________,
passed by the City Council of said City at the meeting held on
______________________and signed by the Mayor on
___________________________, and published in the Ames Tribune on
___________________________.
________________________________
Renee Hall, City Clerk
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