ADU Size Limits by State: Maximum Square Footage Rules Explained

How large an ADU can be depends on a two-layer rule system: the state sets a minimum floor (states must allow at least this large), and the local government can allow up to that floor or more — but cannot go below it. Here is where the major ADU states stand.

California: up to 1,200 sq ft

California Government Code 65852.2 requires local governments to allow detached ADUs of at least 800 sq ft regardless of lot size or floor area ratio limits. Most jurisdictions allow up to 1,200 sq ft for detached ADUs and 500 sq ft for JADUs. Some jurisdictions allow larger ADUs by local ordinance.

Washington: up to 1,000 sq ft minimum floor

HB 1337 (2023) requires Washington cities to allow ADUs of at least 1,000 sq ft or 50% of the primary dwelling's size, whichever is smaller. Cities may allow larger ADUs by local ordinance.

Oregon: 900 sq ft on smaller lots, 1,200 on larger

• Lots under 2,500 sq ft: ADU may be up to 900 sq ft.
• Lots 2,500–5,000 sq ft: ADU may be up to 1,200 sq ft.
• Lots over 5,000 sq ft: ADU may be up to 1,200 sq ft or 50% of primary dwelling, whichever is less.

States without statewide preemption

In states like Texas, Georgia and most of the Southeast, ADU size limits are entirely set by local zoning codes — no statewide floor exists. Size limits often range from 400 to 1,000 sq ft with wide variation by city and zoning district.

ADU laws are evolving rapidly. Always confirm current maximum sizes with your local planning department.