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 Local Laws 126 and 127 (December 2024) now allow ADUs in all 1-2 family homes across the five boroughs. The city is also accepting applications for its basement apartment legalization program, which could bring an estimated 100,000+ illegal basement units into compliance.

Chicago: ADU Program Goes Citywide

After years as a 5-zone pilot, Chicago's ADU ordinance expands to all neighborhoods in April 2026. The city is also launching pre-approved plan sets with 6 designs to speed permitting. This makes Chicago one of the most ADU-friendly major cities in the Midwest.

California: Grants and Continued Expansion

California continues to lead on ADU policy. SB 1211 (multifamily ADU expansion to 8 units) is now fully in effect. A new state-funded grant program offers up to $40K for low-income homeowners building ADUs. And the unpermitted ADU amnesty program has been extended through 2026.

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.

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 SB 1117 continues to preempt local ADU restrictions. The trend is clear: cities across the country are embracing ADUs.