ADU plans in Ontario
ADU plans for Ontario homeowners.
Ontario allows detached ADUs and junior ADUs on single-family lots. We design to the city’s standards and manage the submittal.
Building an ADU in Ontario
What to know before you start.
Based on the city’s published ADU information as of October 2026. Rules change; we confirm the requirements for your address before design.
- Ontario’s handout sets the maximum detached ADU size at 850 sq ft for a studio or one bedroom, and 1,000 sq ft for two or more bedrooms.
- Detached buildings need 6 ft of separation.
- The city does not offer its own standard ADU plan, so most projects use custom plans.
- Permits are filed through the city’s Citizen Portal.
Sources: City of Ontario: ADUs, and the HCD ADU Handbook.
Our ADU package
One flat fee, permit-ready.
- Site visit and measurements
- Layout and elevations you approve first
- Architectural, structural and MEP plans
- Title 24 energy and CALGreen documents
- Submittal to Ontario and plan-check corrections