Zoning: Accessory Dwelling Units


As of 2018-12-18 this document is obsolete. The City Commission ratified changes to the zoning concerning ADUs on that date. Theoretically there will be another set of changes sometime in March/April/May/... at which point this document is will be updated to reflect whatever that result is.

Briefly, the changes on 2018-12-18 were:

  • Floor area ratio changed to 40% (from 25%). Size now has a hard limit of 850sq/ft. Minimum remains 400sq/ft.
  • Height reduced from 25ft to 20ft, except in some extremely rare cases.
  • Minimum lot area of 5,000sq/ft removed, now lots only need to be conforming to the minimum lot size of the zone.
  • Confusion between ADU size and Accessory Structure size has been resolved; and ADU doubles the sq/ft allowed in the Accessory Structure.
  • No change to permitting process.
  • No change to Owner Occupancy or Deed Restriction requirement.
  • No change to unit (1), occupancy (2), or bedroom (2) limit.

Disclaimer & Purpose

This is not an official document; this document is not endorsed by the Grand Rapids Planning Commision, nor are its authors qualified to present legal opinions.

The purpose of this document is to provide an introduction to the regulations related to Accessory Dwelling Units in the city of Grand Rapids, MI as of 2018. Within the Zoning the topic of Accessory Dwelling Units are directly addressed in section [5.9.03]. Other sections of the code may still impact the development of ADUs so we have attempted to cross-reference the most relevant sections. When possible the related regulation is included following the text like: [X.X.XX...]. These references are important as the regulations are implemented in different ways depending upon the section they are from. The different sections of the code are referred to as "Articles". You will want to consider this distinction when making design desicions. Regulations from the Accessory Dwelling Unit section of "Article 9" - starting with [5.9.03. XX...] - can potentially be waived by the Planning Commission in the Special Land Use approval process. Regulations from most other sections cannot be waived or modified. For example: a requirement found in Article 2 - [5.2.XX...] - cannot be waived.

This Article 9 vs. Not Article 9 / "what is a absolute?" is the most confusing aspect of the regulations. For an individual [non-"Developer"] wagering their own money on the permitting process this is going to be a significant source of anxiety. Unfortunately this is the situation; very few ADU projects are likely to be feasible without pushing against Article 9 regulations - especially in relation to size (see Q#9).

The text relating to Article 9 waivers is [5.9.02.A.3]:

All uses listed shall be in accordance with the provisions of Section 5.12.09. The Planning Commission shall have the authority to waive or alter the Use Regulations contained in this Article provided the standards of Section 5.12.12.E. are substantially met.

If your project requires waiver of Article 9 regulations reading section [5.12.12.E] of the code is worthwhile; with particular attention to [5.12.12.E.4]. Section [5.12.12.E.4] is the heart-and-feels section; good relations and input from neighbors along with a continuing dialog with the Planning Department is the best way to achieve "compatible, harmonious and appropriate". []

Zones & Abbreviations

If you are interested in building an Accessory Dwelling Unit the first step is to determine your "Zone District". This Zone District will determine which criteria apply to your project.

The vast majority of lots in the city exists within exactly one Zone District. A Zone District is titled as a combination of a neighborhood type [TN, MCN, MON] and a zone [LDR, MDR, TOD, etc...] For example "TN-LDR" is a "Traditional Neighborhood Low Density Residential" zone, and "MCN-MDR" would be a "Mid-Century Mixed Density" zone. You can find the zoning map here.

Abbreviation Definition Comment
TN Traditional Neighborhood
MCN Mid-Century Neighborhood
MON Modern Neighborhood
LDR Low Density Residential This is the vast majority of the city.
MDR Mixed-Density Residential
TBA Traditional Business Area
TOD Transit Oriented Development
CC City Center
TCC Traditional City Center

If you determine that your lot is split between zones [very rare] you should contact the Planning Department to determine what that means for you.

There are also "Special Districts" and "Overlay Districts". These do not appear to impact the development of Accessory Dwelling Units.


Q#1.) Can I build an Accessory Dwelling Unit in my zone.

If you occupy a property zoned CC, TCC, TBA, TOD, C, or NOS you can receive permission to build an Accessory Dwelling Unit through the Director Review process. The application fee for Director Review is $1,141. One caveat of Director Review approval is that Article 9 regulations cannot be waived; if you want to build an ADU in one of these zones with waiver of one or more Article 9 regulations you can still use the Special Land Use approval as if your lot was in a residential zone (see next paragraph).

If your property is within an LDR or MDR zone you will be required to obtain a Special Land Use Permit. [5.9.02] The application fee for an SLU [Special Land Use permit] is $1,972. See Q#11 for information on the Special Land Use permitting process.

Q#2.) How many Accessory Dwelling Units can exist on a property?

One. Both an ADU included within the primary structure and one within an accessory structure count towards the total limit of one. [5.9.03.A]

Q#3.) How large does my lot have to be to build an accessory dwelling unit?

An ADU is permitted on any lot which meets the minimum for size for its district [5.9.03.B]. Note that requirements for green space and minimum setbacks must still be met.

Q#4.) What is the height limit for an ADU.

An Accessory Dwelling Unit in an accessory structure may be 25 ft. tall with the permission of the Planning Commision [5.9.03.D]. The normal height for an Accessory Structure not containing an ADU is in relation to the zone and lot size; it is typically 14ft. [5.2.08.G.1]

An ADU within the primary structure cannot cause the primary structure to exceed the height of the zone district. [5.9.03.D] The primary height for a zone distinct is described in the following table [5.5.07.A]:

LDR 35ft. 35ft. 35ft.
MDR 45ft. 45ft. 52ft.

The height of the structure is not measured to the peak or highest point. Height is measured to the midpoint between the peak and the eave. (5.2.06.A.2.)

Q#5.) Where may an Accessory Structure containing an Accessory Dwelling Unit be located on the lot.

The dwelling unit may not be located in the front yard [5.9.03.F & 5.2.08.H]. Otherwise the location is principally limited by setback requirements - see Q#9.

Q#6.) What is the maximum occupancy of an Accessory Dwelling Unit

Two. [5.9.03.H] An Accessory Dwelling Unit is also limited to two bedrooms.

Q#7.) What are the limitations regarding the use of an Accessory Dwelling Unit?

  • Either the accessory dwelling unit or the primary structure must be occupied by the owner of the property. [5.9.03.J]
  • An ADU which is operated as a rental property may not be leased for a term of less than 30 days or to more than eleven different parties in a single calendar year. [5.9.03.K]
  • Construction of an Accessory Dwelling Unit will involve the creation of a deed restriction on the property which will prohibit subsequent separation of the Accessory Dwelling Unit from the primary structure. [5.9.03.M] The cost for filing a deed restriction is $30; this is performed via the counties' Register Of Deeds. There may be other feeds related to drafting the deed restriction document.

Q#8.) Is it possible to re-purpose a mobile home or recreational vehicle as an Accessory Dwelling Unit.

No. The restrictions on re-purposed items as accessory structures - including as Accessory Dwelling Units - is very comprehensive [5.2.08.H.1]. It specifically prohibits mobile homes, trailers, railroad cars, and containers.

Tents are also prohibited as Accessory Structures; one can reasonably assume this would include Yurt type structures.

Q#9.) What dictates the minimum and maximum size of an Accessory Structure containing an Accessory Dwelling Unit.

The minimum is straight forward; the minimum size is 400sq/ft [5.9.03.G]

The maximum is constrained by a variety of factors. Principally these are green space requirements, set-backs, and proportionality.

Green Space

Accessory structures are subject to the minimum green space requirements. This limits how much of a parcel can be covered by structures or impervious surfaces

Minimum Greenspace [5.5.06.A]

LDR 40% 50% 60%
MDR 30% 40% 50%

There may be provisions where some covered or otherwise used areas may still be counted as green space - such as the use of porous asphalt in a parking space. Special cases should always be discussed with the city's planning department during the design phase of the project.

Set Backs

  • At least 6ft from the primary structure. [5.2.08.H.1]
  • At least 3ft from the side lot line. [5.2.08.H.1]
  • At least 3ft from any other Accessory Structure. [5.2.08.H.4]
  • An Accessory Structure must be set at least 3ft. from right-of-way of an alley. [5.2.08.H.4]
  • City fire code requires special provisions if a wall is nearer than 5ft. to the property line [5.2.08.H.2.c].


There is a list of features whose footprint is not included in the footprint of the Accessory Structure [] which includes the following items that may possibly be relevant to an Accessory Dwelling Unit: solar panels, decks, and patios.


The floor area of an Accessory Dwelling Unit may not exceed 40% of the gross floor area of the primary structure; with a maximum size of 850sq/ft. [5.9.03.G]. Your primary structure's gross floor area is likely larger than your "square footage" as the square footage frequently referenced is "Residential Square Footage" and does not include space below grade (the basement) - if your basement ceiling is at least 7ft high you may include that space in your calculation regarding the 40%. The 40% boundary is not a significant barrier to ADU development; prior to December 2018 the ration was 25% which was problematic. Under the 40% rule any lot with a primary structure over 1,000 sq/ft gross floor area can meet the minimum 400sq/ftsize. The normal size range for ADUs in other cities is 500sq/ft - 650sq/ft which corresponds to a primary structure size of 1,250 sq/ft - 1,625sq/ft; this is the range of average home sizes in Grand Rapid's traditional neighborhoods.

The definition in the code [5.16.F] of Gross Floor Area is:

The sum of the gross area of each story of a building measured from the exterior limits of the faces of the structure, or from the centerline of walls separating two (2) buildings, including all areas of a building having a height of more than seven (7) feet, as measured from the floor to the lowest point of the ceiling. Measurement of GFA does not include areas used exclusively for vehicle parking or loading and, in industrial areas, storage sheds with less than one hundred and fifty (150) square feet of space, bunkers, electrical substations, smoking shelters, instrument shelters, and similar enclosures.

The table for provided in the Zoning [5.2.08.G.1] describing the maximum sizes for Accessory Structures based on lot size does not necessarily apply if such a structure contains an Accessory Dwelling Unit. The applicability of table [5.2.08.G.1] to Accessory Dwelling units is a matter of interpretation; this does create a grey-area in the code. It may be wise to respect this table in a design if at all possible. This table specifies the following maximum accessory structure sizes (all sizes in sq/ft):

< 5000 624 624 832
5,000 - 7,499 832 832 963
7,500 - 10,999 936 936 1,000
11,000 - 21,999 1,000 1,000 1,200
22,000 + 1,200 1,200 1, 500

Q#10.) Do I need to provide an off-street parking space?

Yes. [5.10.04.C] The creation of an ADU requires the creation of 1 off-street parking space for each bedroom regardless of zone district. A parking space has typically has minimum width of 10ft and a minimum depth of 20ft.

The parking requirement is not a Article 9 requirement; it cannot be waived.

Bicycle parking may not occupy the space required for the parking space.

NOTE: There are some details related to parking, such as how driveways on the property may impact parking requirements, which we are still researching.

Also consider that each Single Family Home [the existing structure] is required by Zoning to itself have two off-street parking spaces. Many lots in the city, particularly in traditional neighborhoods, have zero existing off-street parking spaces. Now that you are adding an ADU to the lot - a significant change - this deficiency may be called into question. Fortunately these requirements for the existing structure are potentially waivable. If your lot has technically inadequate parking be sure to emphasize that you are creating a net increase in parking. If you are replacing a "garage" which is currently not suitable for parking due to size or low door height, as is the case with many old carriage house garages, be certain to point that out so that it is not counted against you in how the initial amount of parking is calculated.

Q#11.) How may an ADU in an Accessory Structure attach to city water & sewer.

Tthe ADU must be connected to municipal water and sewer; this is required by the Residential Building Code. Off-grid dwelling units are not permitted.

There is no requirement by the city that the ADU have a connection to water and sewer independent of the primary structure. However, the text of the Michigan Building Code of 2015 is vague, stating [this text is from a correspondanc with a Grand Rapids Utility Engineer]:

Under Michigan Plumbing Code, two structures may share a sewer lateral as long as they are under the same ownership and on the same parcel. If ownership or the lot is split, sewer separation is required at that time. The wye to the 2nd building must be outside both structures and the sewer lateral must run outside the 45 degree bearing plane of any structure. If you are using a pressurized system with a pump, Larry Olson in Utility Engineering will need to review and approve the pump and proposed location of the private forcemain before work may begin.
A dedicated water service is required for each structure from the main to the meter. On public property, we require a minimum 1" water service made of type "K" copper. We recommend copper for the entire service, but any material accepted under Michigan Plumbing Code may be installed on private property.

We are monitoring two existing ADU projects to see how the water and sewer connections end up being accomplished.

Q#12.) Are "after hours" appointments with City Planners available.

Yes. Subject to each planner's personal schedule after hours appointments are possible on a case-by-case basis. You would need to work this out with the Planning Department, but we are confident you will find them ready and willing to work with you.

Q#13.) How do I acquire an SLU (Special Land Use) permit?

This process is described on the city's website.

You can meet with a city planner with preliminary plans prior to submitting for the permit; this is strongly recommended.

Most importantly the SLU will involve notification of your neighbors concerning your proposals. It is advisable to contact them yourself before hand. Section [5.12.06] of the Zoning code specifically discusses neighborhood meetings and procedures.

If you are fortunate enough to have a friendly Neighborhood Association they can be very valuable in this process; in any case you will probably have to deal with them at some point. A map of the city's recognized neighborhoods is here. In most cases your Neighborhood Association will have a Facebook page.

Q#14.) Are they are any special requirements for a for-rent ADU?

No. The same rental certification process applies to an ADU as any residential property; the required information, including an inspection check-list, can be found here.

The most notable requirement for rental properties beyond a state of good repair is the requirement for 10-year sealed lithium battery or hard-wired with battery back-up smoke detectors These must be present in every bedroom, outside sleeping area(s), and on every level. [9.832, 9.833] The best way to address this is to have hard-wired smoke detectors installed in the unit during construction, even if you do not initially intend for the unit to be for-rent.