There is no single zone label that guarantees an ADU is allowed everywhere. The answer comes from the current use rule for the property’s zone, read with the authority’s definition of the proposed dwelling and its form. An attached addition, interior conversion, garage conversion, and new detached building can follow different rules on the same lot.
Match the parcel to the current use table
Find the parcel on the official zoning map, then use the current zoning code or by-law to check whether the local dwelling use is permitted in that district. Guidance pages are useful starting points, but use tables, planned-district ordinances, amendments, and parcel overlays may change the result. Save the exact zone, section or table, map date, and any effective date used in the check.
Check each project form separately
Do not carry permission from one form to another. Portland’s guidance distinguishes conversions inside a home, additions, accessory-structure conversions, and new detached ADUs. San Diego’s Information Bulletin 400 uses separate tables for ADUs and junior ADUs; its JADU definition is tied to space within a single dwelling or attached garage, and a JADU’s allowable zones are not identical to the broader ADU question. Boulder lists local districts where ADUs are allowed but notes that a property with a prior PUD approval may need a minor modification before a building permit. Ontario Regulation 462/24 describes covered additional-residential-unit configurations while preserving specified municipal by-law standards and parcel checks. The same distinction matters when comparing an accessory building with a self-contained dwelling.
Understand the kind of permission
Record whether the table says permitted, conditional, discretionary, prohibited, or unclear. A conditional use or variance is a process for asking the authority to assess a proposal; it is not a promise of approval. Higher-level rules may set a minimum opportunity or constrain local restrictions, while still preserving site, environmental, building, or service requirements. For example, Oregon’s ORS 197A.425 describes an ADU allowance for qualifying population, urban-growth-boundary, and zone contexts, while the 2025 Small Cities Housing Model Code requires the applicable city adoption or application to establish where its standards apply. Neither source alone decides an Oregon parcel. Ontario Regulation 462/24 likewise describes covered additional-residential-unit configurations while preserving specified municipal by-law standards and parcel checks. England’s planning-permission framework and the separate rules of Scotland, Wales, and Northern Ireland should not be collapsed into one “UK zone” result.
Check what zoning does not decide
Even where a use is allowed in principle, overlays, a prior approval, flood or heritage controls, primary-dwelling status, lot conditions, access, utility capacity, and building regulations can remain decisive. Existing construction may also require permit-history review. Keep those checks separate and route them to the authority that administers each rule.
For examples of local use-table matching, compare the San Diego ADU/JADU screen, Toronto garden-suite zones, and Winnipeg attached versus detached suites. For an individual property, confirm the present code and map with the responsible authority.