ADU Laws That Changed in 2026 — State-by-State Breakdown

The ADU landscape is shifting faster than ever. In 2026 alone, multiple states have passed landmark legislation making it easier for homeowners to build accessory dwelling units. From Massachusetts requiring all municipalities to allow ADUs by right, to New York City legalizing basement apartments, here is every major change you need to know.

Massachusetts: ADU By Right Statewide

The Affordable Homes Act §8 is the biggest ADU reform in the Northeast — ever. Effective February 2025, all 352 Massachusetts jurisdictions must now allow ADUs by right in single-family zones. No special permits. No variance hearings. This opens up ADU development for millions of homeowners who previously faced years of red tape.

New York City: Basement ADU Legalization

NYC's City of Yes (Local Laws of December 2024) now allows ADUs in many 1-2 family homes across the five boroughs — though major exclusions apply (historic districts, certain low-density R1A/R2A/R3A zones outside the Greater Transit Zone, flood-prone basements/cellars), and the owner must occupy one unit at initial occupancy. The city is also accepting applications for its basement apartment legalization program.

Chicago: ADU Program Goes Citywide

After years as a 5-zone pilot, Chicago's City Council voted in September 2025 to make the ADU ordinance permanent, effective April 2026. ADUs become as-of-right citywide in multifamily (RT/RM) zones, while single-family (RS) zones still require the local alderperson to opt in — so coverage is citywide but not uniform. The city is also launching pre-approved plan sets to speed permitting.

California: Grants and Continued Expansion

California continues to lead on ADU policy. SB 1211 (multifamily ADU expansion to up to 8 detached units) is now fully in effect. The CalHFA ADU Grant (up to $40K for predevelopment costs) is currently paused — funds were fully allocated in December 2023 and there is no confirmed relaunch as of 2026, and CalHFA warns that anyone promising to secure it now is running a scam. The unpermitted-ADU amnesty pathway (AB 2533) remains available.

Seattle: End of Single-Family Zoning

Seattle has eliminated single-family zoning entirely, allowing up to 4 homes per lot in Neighborhood Residential zones. The ADU/DADU distinction has been removed, simplifying the permitting process. Washington state's HB 1337 continues to reshape ADU policy statewide.

New Statewide Laws: Virginia, Montana & Arkansas

The statewide push kept going in 2025–2026. Virginia's SB 531 (signed April 2026, effective July 1, 2027) will require localities to permit ADUs by right in single-family zones and caps the permit fee at $500 — though localities that already had an ADU ordinance before January 1, 2026 (such as Arlington and Alexandria) are exempt and keep their existing rules. Montana requires one ADU by right on any single-family lot statewide (SB 528, effective 2024), and its 2025 follow-up SB 532 removed the size cap and added expedited review. Arkansas' Act 313 (effective January 1, 2026) requires cities to allow ADUs by right, with no added parking, no owner-occupancy mandate, and permit fees capped at $250.

Denver, Phoenix, and More

Denver now allows ADUs on all residential lots citywide. Phoenix expanded ADU-allowed zones to cover all single-family residential areas. Arizona's HB 2720 requires larger cities to permit ADUs (one attached plus one detached) by right on single-family lots. The trend is clear: cities across the country are embracing ADUs.