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Legalize housing
Accessory Dwelling Units (ADUs)
Also known as ADUs, in-law suites, granny flats, backyard cottages, carriage houses, ohana units, casitas, guesthouses, second units, garage conversions
ADUs use existing infrastructure to add much-needed housing variety to established residential areas.
Written by YIMBY LawWhat Accessory Dwelling Units Do
An accessory dwelling unit (ADU) is a smaller, independent residential dwelling unit located on the same lot as a stand-alone single-family home. Internal, attached, and detached ADUs all increase housing affordability while also presenting attractive options to diversify housing stock without drastically changing neighborhood density.
Example legislation
Bills that carry this policy, passed and in progress.
- Passed
“Any accessory use or accessory structure permitted within all residential zoning districts shall be permitted by right.”
Read the billRichmond, VA’s Ordinance No. 2023-196 (2023)
- Passed
“An accessory dwelling unit shall be permitted up to at least 1,200 square feet and shall not be limited based on a percentage of the primary dwelling.”
Read the billArizona’s HB 2720 (2024)
Why localities should pursue accessory dwelling units
The problem
High-opportunity neighborhoods with strong access to jobs, schools, and transit are locked to one home per lot. Homeowners who could add a smaller, more attainable home — and the rental income that helps them afford the mortgage — are stopped by fees, discretion, parking rules, and occupancy requirements that make ADUs infeasible.
The fix
Allow ADUs by right with minimal restrictions beyond a size cap. ADUs use existing homes and infrastructure to add gentle density, help homeowners build wealth, give families private multigenerational space, and cost less to build than full-size homes — no new land, roads, or utilities.
The politics
Start with the housing need. Accessory dwelling units (ADUs) offer cities a practical way to add housing without changing neighborhood character dramatically. They create opportunities for homeowners to build additional homes for family members, renters, or aging parents, while making better use of existing lots and infrastructure.
Next, look at state law. Many states have already passed legislation requiring cities to allow ADUs, limiting local restrictions on their size, placement, parking requirements, and permitting processes. Where state law is strong, cities should focus on bringing local ordinances into compliance rather than creating additional barriers. Where state protections are limited, the first campaign may be at the state level to establish clear, consistent rules that prevent cities from unnecessarily restricting ADU development.
Build a broad coalition early. Homeowners, housing advocates, aging-in-place organizations, and small-scale builders can all make the case for ADUs from different perspectives. Emphasize the benefits that resonate locally: more housing options for families, rental income for homeowners, multigenerational living, and naturally affordable homes.
Timing matters, too. Cities should pursue ADU reforms when updating their zoning codes, responding to state mandates, or looking for ways to address housing shortages without major new infrastructure investments. Keep the rules straightforward, streamline permitting, and eliminate unnecessary costs. The goal is to make building an ADU a predictable, accessible option—not another complicated entitlement process.
The impact
Gentle density in high-opportunity neighborhoods
PEWADUs use existing homes and infrastructure to support smaller, more attainable housing in areas with strong access to jobs, schools, and transit. In doing so, they expand access to high-opportunity neighborhoods without requiring large-scale redevelopment.
Homeowner benefits
AARPADUs can provide rental income that helps homeowners afford their mortgages, manage everyday expenses, and build long-term wealth, all while providing much-needed housing in their neighborhoods.
Multigenerational living
Elemental GreenFor seniors who want to age in place, ADUs provide a separate, private living space on the same property as the main home that balances closeness with independence. Additionally, they offer financial benefits such as shared living costs for younger family members who can’t afford high housing prices in their area.
Affordable housing
Housing Solutions LabADUs are typically less expensive to build than large single-family homes because they maximize existing land and infrastructure. Since they are added to current properties, there is no need to purchase new land, build new roads or utilities, or construct costly features like parking structures or elevators.
“”Well-designed ADUs increase property values and neighborhood desirability.
YIMBY Law
Crafting the policy
ADU legalization is often the most politically viable form of zoning reform because it expands housing supply while directly benefiting existing homeowners. By granting property owners the right to add small secondary units, states can increase density in a subtle, incremental way. This broad appeal helps explain why policymakers are often more willing to remove local restrictions on ADUs than embrace other types of housing reform.
Must include
- By-right development
- Limited restrictions beyond size
Watch out for
- Aesthetic requirements
- Inclusionary and/or affordability requirements
- Unnecessary expenses & fees
- Local discretion
- Owner-occupancy requirements
- Parking minimums
Why each one matters
After it passes
Allowing ADUs by ordinance is ineffective without enforceable requirements. If cities can delay or refuse to adopt compliant rules, ADU development stalls.
- 1
Ensure legislation has a clear and close effective date
- 2
Identify the enforcement mechanism
An appeals process or legal recourse when projects are wrongly denied
- 3
Award attorney's fees to the prevailing party in disputes
Make the case
What to say at public comment, in a letter to council, or to a neighbor.
Neighborhood opposition can strongly influence elected officials and the policy process even when policies can benefit a neighborhood. When advocating for ADUs, framing is critical. Proposals should be positioned not simply as a gentle increase in density but also as a simple way to boost property values and increase neighborhood desirability.
Talking points
Say them at public comment, put them in a letter to your council, or send them to a neighbor. Copy any one.
Likely allies
The groups that tend to show up for it.
6 likely allies
- AARP
- Casita Coalition
- Homeowner & neighborhood associations
- Planning associations
- REALTOR & homebuilder associations
- Strong Towns & Sierra Club
Wins & momentum
Where it has already passed.
3wins since 2024
- 3
- 4
Related primers
Bringing this to your city council?
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