Accessory dwelling units

A smaller, independent home on the same lot as a single-family house — internal, attached, or detached. ADUs increase affordability and diversify the housing stock without drastically changing neighborhood density.

Legalize housingUpdated Apr 2026

What it does: Legalizes accessory homes on single-family lots
Works at: City · State
Cost to government: ~$0 — homeowners build, cities permit
Momentum: Chapter wins in MD & Hawai'i

Why it matters

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 misconception to defuse early: ADUs aren't commercial rentals taking over the block — most house elderly parents, adult children, and caregivers. And well-designed ADUs increase property values and neighborhood desirability, not the reverse.

Craft the policy

What separates versions that produce homes from versions that produce headlines.

Include

By-right development
Streamlined, expedited permitting: an ADU that meets the existing rules for a single-family lot is approved. Aim for minimal restrictions.
Example language: “Any accessory use or accessory structure permitted within all residential zoning districts shall be permitted by right.” — Richmond, VA
Bare-minimum restrictions beyond size
A maximum size relative to the primary dwelling is a reasonable rule; nearly every additional requirement renders ADUs unaffordable. Keep the list short enough that projects stay financially viable.
Example language: “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.” — Arizona HB 2720

Avoid

Aesthetic requirements
Matching-design-and-materials rules eliminate development opportunities. The value of the housing outweighs a visual mismatch.
Affordability mandates
Inclusionary requirements on a homeowner project reduce the ability to recoup the investment — and discourage construction entirely.
Unnecessary expenses & fees
Eliminate development fees, or limit them to actual staff effort. Materials, labor, and legal costs already add up.
Local and HOA discretion
Discretion is how projects get delayed, denied, or inflated in cost. Use objective, clear standards instead.
Owner-occupancy requirements
They add paperwork, reduce rentability, and discourage construction.
Parking minimums
Added cost and space requirements that make many ADUs infeasible outright.

After it passes — implementation checklist

1Set a clearly defined, near-future effective date — cities can't be allowed to delay or refuse adopting compliant rules
2Identify the enforcement mechanism: an appeals process or legal recourse when projects are wrongly denied
3Award attorney's fees to the prevailing party in disputes

Make the case

“Well-designed ADUs increase property values and neighborhood desirability.”

“Most ADUs house elderly parents, adult children, and caregivers — not commercial rentals.”

“ADUs maximize existing infrastructure instead of consuming green space — and the small, energy-efficient units are environmentally friendly by design.”

Likely allies — and why they show up

Casita Coalition: The ADU movement's subject-matter experts
AARP: Multigenerational living and aging in place
REALTOR & homebuilder associations: More value and more small-scale construction per lot
Planning associations: Gentle density that fits existing plans
Homeowner & neighborhood associations: Wealth-building for current residents
Strong Towns & Sierra Club: Incremental infill on existing infrastructure

Wins & momentum

—Howard County, MDYIMBY Maryland advocated by-right ADUs, unlocking thousands of potential unitsYIMBY-backed
—Kauai County, HIHawai'i YIMBY won ADU legislation with an occupancy increaseYIMBY-backed
—Honolulu County, HIOne ADU plus one Ohana unit allowed per lot — keeping Hawaiian families from being displaced to the mainlandYIMBY-backed

Research & resources

GuideOvercoming barriers to ADU developmentEnterprise Community Partners
ExplainerADU basicsAmerican Planning Association
ResearchADUs and the housing crisis · 7 communities that got ADU policy rightMercatus Center
Why onerous requirements bite — and who fixed them
ResearchADU reform in MassachusettsPioneer Institute
DataZoning maps with ADU filtersNational Zoning Atlas

Related playbooks

Parking reform

End mandatory parking minimums — a hidden tax that adds tens of thousands of dollars to every new home.

Yes in God's backyard

Let churches and faith institutions build homes on land they already own.

Single-stair reform

Legalize the small, family-sized apartment buildings most of the world builds — one stair, up to six stories.

Bringing this to your city council?

You don't have to make the case alone. Our chapters have passed policies like this before — join one, or start one, and bring the movement with you.

Become a member Find your chapter

All solutions