What applies locally
An ARU is a self-contained dwelling associated with eligible detached, semi-detached or street-townhouse housing, either within the main building or within an accessory building.
St. Thomas, ON suite & ADU rules
Permission first. Construction second.
St. Thomas publishes a 2026 additional residential unit guidebook for homeowners.
Main home
Secondary / ADU
One property · more than one approval layer
Local rule · reviewed 8 October 2026
What the municipal rules say
St. Thomas publishes a 2026 additional residential unit guidebook for homeowners.
Important limits and exceptions
The guide is not a zoning approval for a parcel. Check the local lot and zone, access, water/sewer service, parking, building code and permit before creating an internal or detached unit.
Before work begins: confirm the lot’s actual zoning, mapped overlays, legal parcel characteristics, servicing and applicable building permit conditions with the municipality.
Indexing: City guide: enacted rules summarized; parcel permit not verified. This page is information, not municipal permission for a specific address.
Property address check
Check a St. Thomas property by address.
Enter a street address. We’ll match it to St. Thomas and show available municipal planning information that requires independent verification.
Uses Natural Resources Canada’s national Geolocator to match the address. Any planning result is preliminary and must be checked against the current municipal bylaw and permit office.
Dedicated suite/ADU sourceReviewed 2026-10-07
The local suite route in St. Thomas
Open the official St. Thomas suite source ↗Neighbouring communities in Central Ontario can implement additional housing differently. Keep the municipal portion of the check specific to St. Thomas.
Ontario: the provincial layer
Ontario additional residential unit framework ↗What the local source tells you
Source reviewed October 7, 2026. Confirm the current municipal page and bylaw before relying on a property-specific result.
Can you build here?
Here is the municipal framework; parcel eligibility is not verified in St. Thomas.
This is the simple build-direction summary. The exact property still has to meet its zoning, site, servicing and permit requirements.
Internal additional unitConditional — verify
Detached garden / backyard unitConditional — verify
DuplexProperty-specific
TriplexProperty-specific
FourplexProperty-specific
Before you build: confirm the exact property, zoning and permit path with St. Thomas.
Next planning steps
Local rules still need verification before pricing before you request a quote.
This preliminary guide does not answer whether a particular parcel is approved. The next two steps are budgeting and contractor scoping; neither replaces municipal approval.
1 · BudgetEstimate renovation costs in St. ThomasOpen the matching Home Cost Canada city page, then adjust the project and scope.Open cost planner →2 · ContractorFind a local contractorHomeSelect is a separate contractor-matching service. Use it after the zoning and permit path are understood.Start contractor match →
Planning sequence: rules → budget → written scope / contractor. Cost models and contractor matching do not determine whether the municipality will approve the work.
How this guide was verified
Guide verification: Official-source research summary. This guide provides linked municipal research; a complete enacted-bylaw, zoning-map and amendment cross-check has not been documented for this municipality.
Property confidence: Not assessed. City-wide guidance does not confirm permission for a particular parcel. Check official zoning, overlays and permits. How verification works →
Municipal evidence check — October 12, 2026
Checked against municipality-published material: The City publishes its 2026 ARU Guidebook and defines internal, attached and detached ARUs for qualifying residential properties.
Outstanding: Check the guidebook against adopted zoning, number-of-unit and lot design requirements and property permits; a guidebook is not a full legal signoff.
Verification status: Targeted municipal-source check completed. This is not an independent certification of all enacted bylaw amendments, zoning maps or any individual property.
Official St. Thomas sources
St. Thomas — official local guidance ↗Ontario — provincial framework ↗Official municipal source checked (Oct 2026) ↗
Municipal adoption / zoning evidence reviewed October 8, 2026 ↗
Reviewed October 8, 2026. Check the current bylaw and the mapped parcel directly with municipal planning before constructing or legalizing housing.