Cities urgently need new housing, whether its due to aging stock or an influx of residents. Accessory Dwelling Units (ADUs) are an increasingly popular choice for cities looking to increase density, while also providing homeowners revenue options and developers additional choices on how to approach density in populated areas. In 2023, for example, Seattle saw a 250% increase in ADU permit requests - almost 1000 units.
What is an ADU?
An ADU, also called an in-law unit, mother-in-law unit, secondary dwelling unit, granny flat, or carriage house, is a secondary housing unit on a single-family residential lot. It is self-contained and includes all the basic facilities needed for day-to-day living, independent from the main home, such as a kitchen, sleeping area, and a bathroom. ADUs can be internal to the main house (often in a basement), directly adjacent to the main house as an addition, or detached in a yard or lot.
How are cities and states approaching ADUs?
There are a several requirements that local and state governments define when integrating ADUs into their housing stock. Those decision points and limitations include:
Structural Definitions
- Size limitations in square feet
- Height Restrictions, which can differ between attached and detached units
- Property line setbacks, that may differ from rules for the main building
- Number of Occupants and occupancy rules, (ie: does the owner need to live on site)
- Safety considerations, such as egress requirements and fire safety
- Sustainability Requirements, such as energy efficiency and water conservation measures
- Parking requirements, such as number of spots, on or off-street parking, or exemptions due to proximity of public transportation
Design standards meant to keep the integrity of a community can include:
- Landscaping
- Design compatibility, such as architectural style
- Historic district requirements, like window type and door placement
Process
- Permitting process
- Zoning
- Incentives
- Additional approvals, such as meeting historical requirements, HOAs and public hearings
Where do citizens get stuck when trying to understand ADU requirements?
City codes are complicated, difficult to navigate, and refer frequently to state and international code books. Citizens are not equipped to dive into specific requirements, nor do they necessarily understand terms like “setbacks” or “egress”, making it difficult for them to know what to look for.
To solve this issue, many cities are making checklists for citizens to help them navigate what is needed in their area. The City of Boston, for example, worked across multiple departments to create a checklist for citizens that explains the specific codes and requirements needed for an ADU to meet code requirements. This collaboration required work across the Fire Department, Inspectional Services, Housing, Planning, and the New Urban Mechanics, who created a comprehensive view, taking the guesswork out of development.
Many cities and counties are following similar methods, while others are looking to provide an easy to implement, standardized plan that can be built while taking the guess work out of requirements.
Get started with ADU requirements!
ADUs can be a huge benefit to cities looking to expand their housing stock while also benefiting their citizens. Providing citizens and developers with clear guidelines is a fast way to create density. To get ready:
- Determine building code and zoning requirements. Understand what existing local and state codes allow, and check what other cities are doing that can apply to your community. We used Fordje’s Code Clarifier to see how various cities are implementing ADUs into their housing stock, as well as differences between those cities due to unique needs and characteristics. We then dove deeper on city websites.
- Provide a comprehensive checklist that interested parties can use to easily understand what is needed and if this type of development is possible on their parcel.
- Let people know! Get the word out and share what’s possible so your local community can get involved.
