The reliable way to answer “can I build an ADU here?” is to identify the parcel and follow the rules of the authority that governs it. A municipality’s ADU summary can help you screen a project, but it does not establish that a particular property qualifies.
1. Identify the parcel and the decision-maker
Start with the street address or parcel number in the official municipal or county property map. Confirm the municipality, zoning authority, and any separate planning, conservation, heritage, or agricultural authority. A postal city name may not be the zoning jurisdiction. Where state or provincial law changes local zoning powers, read that rule together with the local code rather than treating either source as the whole answer.
2. Translate the project into the local definition
ADU is a useful search term, not a portable legal classification. Portland describes an ADU as a smaller independent home on the same lot as a main home and recognizes interior conversions, additions, accessory-structure conversions, and detached construction. Toronto distinguishes a garden suite in an ancillary building from a laneway suite beside a public lane. The District of Columbia’s guidance links the Building Code term “accessory dwelling unit” to the zoning term “accessory apartment.” Other authorities use terms such as secondary suite, coach house, or additional residential unit. Match the proposed unit’s facilities, location, relationship to the main dwelling, and project state to the local definition before applying a zone rule.
3. Read the actual use rule for the zone
Check the current zoning designation and the applicable use table or by-law section. Record whether the proposed form is permitted, permitted with stated conditions, subject to discretionary review, not permitted, or not established by the available source. Do not infer permission from a residential label, a neighboring property’s unit, an online listing, or a summary for another city.
4. Test the conditions that can change the screen
Check the primary dwelling type and status, unit count, lot measurements, overlays, access and servicing, and any prior approval or permit history. A state-level permission may preserve local environmental or wastewater limits. An existing structure may need a different route from a new proposal; physical presence or tax records do not prove that a unit was legally permitted. Private covenants and HOA rules are separate from public zoning and may impose additional constraints.
5. Record a qualified answer
Keep the conclusion tied to its evidence: the parcel identifier, authority, zone, exact source and section, source date or rule status, project form, and unresolved conditions. If the map, legal definition, amendment status, or parcel record is uncertain, report “not established” and ask the authority for confirmation. Do not turn an incomplete screen into a yes or no.
After the zoning screen, check project-form eligibility, lot and unit-count rules, and any overlay qualification.