A comparison of ADU friendly Cities and How to become one

A COMPARISON OF ADU FRIENDLY CITIES AND HOW TO BECOME ONE

A few weeks ago I got in contact with some people from the Department of City Planning in Pittsburgh to discuss their previous effort to launch an ADU pilot program as well as the future of accessory dwelling units in Pittsburgh, and it got me thinking – What makes an ADU friendly City and how do you get there if say you want an ADU on your property now?

Although I’ve been a licensed architect for a few years, I’m a newcomer to writing about this space, so as part of this exercise, I wanted to really take a deep dive into what was going on in some key cities across the country. I focused on a geographically diverse selection of cities that currently allow ADU’s so that the reader can

A.) Look at the opportunities and limitations set forth by urban zoning commissions around the country

B.) Generate ideas for how they might approach decision makers should they attempt to get their property zoned to build an ADU if they are in a region that doesn’t currently have a process in place.

While ADU’s can take many additional forms in the way of conversions and additions, my research focused on policies specifically related to detached ADU’s. I looked at seven different requirements for seven different cities. They are as follows:

Development and Setback Requirements
Square Footage Requirements
Lot Size Requirements
Parking Restrictions
Rental Opportunities
Maximum Height allowance
Owner Occupancy Requirements

See below:

**Please note zoning policies are subject to change and while a best effort was made to report up to date information, some of this information may not reflect the most current amendments**

Yes	No
AUSTIN	SEATTLE
	PORTLAND
CHARLOTTE	SAN FRANCISCO
	MINNEAPOLIS
	PITTSBURGH (PILOT)
	DENVER

Owner Occupancy Requirement

Yes	No
MINNEAPOLIS	SEATTLE
CHARLOTTE	PORTLAND
PITTSBURGH (PILOT)	SAN FRANCISCO
DENVER	AUSTIN

Requires Additional Parking

SEATTLE

Development and Setback Requirements:

May not be located within the front yard required by subsection 23.44.014.B, except on a through lot pursuant to Section 23.40.030 or Section 23.40.035

A detached accessory dwelling unit may not be located within the side yard required by subsection 23.44.014.B except as provided in subsection 23.44.014.C.3 or 23.44.014.C.4

A detached accessory dwelling unit may be located within a required rear yard if it is not within 5 feet of any lot line, unless the lot line is adjacent to an alley, in which case a detached accessory dwelling unit may be located at that lot line.

Location of Entry An entrance facing any side or rear lot line must be setback 10 feet from that lot line unless it abuts an alley or other public right-of-way.

Seattles Municipal code is below for the above references.

Chapter 23.44 – RESIDENTIAL, SINGLE-FAMILY | Municipal Code | Seattle, WA | Municode Library

Maximum height allowance:

18’ Conditions apply

Square Footage Requirement:

A DADU is limited to 1,000 square feet of gross floor area in neighborhood residential zones

Lot Size Requirement:

Lot size required for a DADU is 3,200 square feet in neighborhood residential zones

Parking Restrictions:

No off-street parking is required for an ADU – no existing required parking may be eliminated to accommodate an ADU unless replaced

Rental Opportunites:

Not mentioned

Owner Occupancy Requirement:

The property owner is not required to live on the property where an ADU(s) is located. This rule was amended in 2019.

Key Sources:

Seattle SDCI Tip 116B – Establishing a Detached Accessory Dwelling Unit (DADU)
Accessory Dwelling Unit – SDCI | seattle.gov
Seattle SDCI – 2022 Accessory Dwelling Units Presentation, Seattle Home Fairs

PORTLAND

Development and Setback Requirements:

Detached ADUs must be set back 40 feet from a front lot line or behind the rear building line of the primary structure.

Max height:

20 feet, conditions apply

Square Footage Requirement:

The maximum size of an ADU may be no more than 75% of the living area of the primary structure (or larger of two units in a duplex) or 800 square feet whichever is less.

Lot Size Requirement:

When two ADUs are proposed on a lot with a house or one ADU is proposed on a lot with a duplex in R7 through R2.5 zones, minimum lot sizes apply:

Minimum Lot Area (Table 205-1)

(it appears not with 1 house + 1 adu only assuming its with a single family residence)

Zone	Minimum Lot Area
R7	5,000 SF
R5	4,500 SF
R2.5	3200 SF

To see where your home is zoned in Portland, refer to the map below.
Zoning Quarter Section Maps | The City of Portland, Oregon (portlandoregon.gov)

Parking Restrictions:

Additional on-site parking is not required for an ADU. However, if parking is required for the existing dwelling unit/s, that parking must either be retained or replaced on-site.

Rental Opportunities:

Additional on-site parking is not required for an ADU. However, if parking is required for the existing dwelling unit/s, that parking must either be retained or replaced on-site.

See more on Short-Term Rentals in Portland below.

33.207 Accessory Short-Term Rentals | Portland.gov

Owner Occupancy Requirement:

Key Sources:

Zoning Requirements for an Accessory Dwelling Unit | Portland.gov
ADU GUIDE — zenbox design

SAN FRANCISCO

Development and Setback Requirements:

At least half of front setback must be permeable and 20% must be unpaved and landscaped with plant material
Side and rear set-backs are determined by additional zoning and fire requirements. There are differences in open space requirements based on whether you are in a single family zone.

For SF zoning map, look here.
BIGmap (sfplanning.org)

Max height:

16′

Lot Size Requirement:

No per AB 68

Square Footage Requirement:

ADU’s must be a minimum of 220 SF and a maximum of 1,000 SF.

Parking Restriction:

Additional parking is not required for an ADU.

Rental Opportunities:

Strengthens the existing requirement that ADU’s be used for rental terms of at least 30 days by requiring local governments mandate 30-day minimum rentals.

Owner Occupancy Requirement:

While Junior ADU’s inside converted space have owner occupancy, detached units do not.

Key Sources:

Accessory dwelling unit (ADU) | San Francisco (sf.gov)
New California Housing Laws: AB 68 Accessory Dwelling Units | Farella Braun + Martel LLP – JDSupra

DENVER

Development and Setback Requirements:

The zoning code requires detached ADUs be located in the rear 35% of the zone lot depth with 3- to 5-foot side setbacks, depending on lot width, and 5-foot rear setbacks. Increasing the setbacks on larger lots and/ or lots without alleys could help create a more context sensitive ADU. However, increasing the setbacks could reduce the develop-able area for a detached ADU to less than the maximum size allowed. Bulk Plane restrictions also apply.

Max height:

Detached ADUs are limited to a maximum height of 1.5 stories and 24’

Square Footage Requirement:

Square footage allowance is a factor of lot size

6,000 sq ft or smaller 650 sq ft
6,001-7,999 sq ft 864 sq ft
8,000 sq ft or larger 1,000 sq ft

https://denvergov.org/maps/map/zoning

Lot Size Requirement:

The minimum lot size and depth for ADUs are defined by the zone districts where they are allowed. The Urban and Urban Edge zone districts that allow detached ADUs range in size from 3,000 to 10,000 square feet and do not specify a minimum lot depth required for detached ADUs. However, the S-SU-F1 zone district, which is the only Suburban district that allows ADUs, requires a minimum zone lot area of 8,500 square feet and only allows detached ADUs on lots that are at least 150’ deep

Parking Restriction:

Currently there is no off -street parking requirement for single unit dwellings or ADUs

ADU Time restraints:

ADUs may be rented out as a short-term rental as long as the owner of the ADU lives on the property and maintains permanent residence there

Owner Occupancy Requirement:

The owner of the zone lot on which an ADU use is maintained must occupy either the primary dwelling unit or the ADU as the owner’s legal and permanent residence

Background Report FINAL.indd (denvergov.org)

AUSTIN

Development and Setback Requirements:

Buildings must be separated by a minimum of 10 feet (front to back and side to side) of primary structure

Max height:

30’ or two stories

Lot Size Requirement:

Minimum lot size for ADUs on SF-3 zoned lots is 5,750 square feet. Find your zone below.
Property Profile (austintexas.gov)

Square Footage Requirement:

Maximum size of an ADU is 1,100 square feet or 0.15 FAR whichever is smaller.

Parking Restriction:

One parking space must be provided for the ADU in addition to the main structure parking.

Rental Opportunities:

Use as a short-term rental is limited to a maximum of 30 days per year for ADUs constructed after October 1, 2015. Type 2 short term rental where the owner doesn’t live there is not allowed.

Owner Occupancy Requirement:

The property owner is not required to live on the property where an ADU(s) is located

Key Sources:

document.cfm (austintexas.gov)
https://www.austintexas.gov/page/accessory-dwelling-units

MINNEAPOLIS

Development and Setback Requirements:

No detached accessory building or open parking space shall be located closer than six (6) feet from the habitable space of a dwelling of any type, except that detached accessory dwelling units may be located closer than six (6) feet from an open parking space. Detached parking garages serving residential uses and detached accessory dwelling units shall be located entirely to the rear of the principal residential structure.

Max height:

20 feet with some conditions

Lot Size Requirement:

Not mentioned, some sources say none

Square Footage Requirement:

The gross floor area of a detached accessory dwelling unit, including any areas designed or intended to be used for the parking of vehicles and habitable floor area on all levels, shall not exceed one thousand three hundred (1,300) square feet or sixteen (16) percent of the lot area, whichever is greater. In no case shall the gross floor area exceed one thousand six hundred (1,600) square feet or exceed the gross floor area of the principal dwelling, whichever is less. c. When a lot includes a detached accessory dwelling unit, the combined floor area of the footprint of the detached accessory dwelling unit, and all other accessory structures and uses designed or intended to be used for the parking of vehicles, shall not exceed six hundred seventy-six (676) square feet or ten (10) percent of the lot area, whichever is greater, not to exceed one-thousand (1,000) square feet.

Parking Restriction:

There is not a minimum or maximum parking requirement for the principal structure or for the accessory dwelling unit No detached accessory building or open parking space shall be located closer than six (6) feet from the habitable space of a dwelling of any type, except that detached accessory dwelling units may be located closer than six (6) feet from an open parking space. Detached parking garages serving residential uses and detached accessory dwelling units shall be located entirely to the rear of the principal residential structure.

(2003-Or-017, § 3, 1-31-2003; 2013-Or-245, § 2, 12-13-2013; 2014-Or-120, § 4, 12-5-2014)

Owner Occupancy Requirement:

The property owner must reside in either the main house or in the ADU as their primary residence. This restriction must be recorded on the deed.

Rental Opportunities:

Not mentioned

Key Sources:

CHAPTER 537. – ACCESSORY USES AND STRUCTURES | Code of Ordinances | Minneapolis, MN | Municode Library

https://www2.minneapolismn.gov/media/content-assets/www2-documents/business/Accessory-Dwelling-Unit-Application.pdf

CHARLOTTE NC

Development and Setback Requirements:

The ADU shall be located in the rear yard and not be any closer than 15 feet to a rear property line within the required side yard dimension. If the ADU is located within a garage structure and the parcel abuts an alley the structure may be located 5 feet from the rear property line if the garbage is accessed from the alley.

Max height:

N/A

Square Footage Requirement:

The adu shall be limited to 50% of the principal structure and cover no more than 30% of the rear yard, though not to exceed 800 SF

Lot Size Requirement:

None available

Parking Restriction:

1 Space is required

Owner Occupancy Requirement:

The Adu and Principal dwelling shall be owned by the same person.

Short Term Rental:

Not Mentioned

Permit_AccessoryStructure.pdf (charlottenc.gov)
AccessoryDwellingUnits.pdf (charmeck.org)

PITTSBURGH

Development and Setback Requirements:

No mention in presentation

Max height:

30 feet or two stories

Square Footage Requirement:

120 – 800 SF

Lot Size Requirement:

None

Parking Restriction:

Parking is not required for ADUs

ADU Time restraints:

ADU’s may not be leased for terms shorter than 30 days.

Owner Occupancy Requirement:

Yes

PowerPoint Presentation (pittsburghpa.gov)

How to make a change in your city and community

1.) Have in-roads with people who make the policies

It may be worthwhile to use your connections or build new ones with policy-makers.

This was the case with Pittsburgh’s ADU Pilot Program.

There was a prominent architect in the Pittsburgh area working with the Bloomfield-Garfield Corporation and the Department of City Planning to both establish an ADU Pilot program and get his own designs approved. He thought it might be a nice opportunity to move on an ADU project and that they could get people locally educated on the benefits of ADU’s.

https://www.wesa.fm/development-transportation/2018-06-11/how-granny-flats-could-create-more-affordable-housing-in-pittsburgh
https://bloomfield-garfield.org/about/

2.) Use change.org for petitions

Change. Org Petitions appear to have had some impact in facilitating new ADU Policy. See this successful petition from Los Angeles from a few years ago.

Petition · Yes In My Back Yard! I WANT MY ADU! · Change.org

and one was also being used to support ADU legislation in Raleigh.

3.) Apply for a conditional use permit

Below is a post explaining the Conditional Use Permit Process.

Conditional Use Permit: Everything You Need to Know – My Site Plan

While this is by no means a guarantee, it has been successful. In a discussion with a planning manager from the Salt Lake City Planning Department, they said that they do occasionally approve Conditional Use Permits for ADU’s. It may be worth a try in your community. An example of one project that was approved using this approach can be found in the link below.

http://www.slcdocs.com/Planning/Planning%20Commission/2022/04.%20April/Staff%20Report%20PLNPCM2022-00091%20ADU%20617%20E%20Driggs%20Ave.pdf

4.) Rezoning if appropriate

Similar to Conditional-Use permits, the but it does have precedent. A City-Council member in Denver reached out to three neighborhoods in Denver to see if this was something they were interested in and the community was later rezoned. It may be the other way around, and you may have to reach out to them, so I posted a helpful link below on that as well.

3 more Denver neighborhoods get ADU rezoning – Axios Denver

How to Get Elected Officials to Listen: 11 Steps (with Pictures) (wikihow.com)

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