Sarnia zoning for small homes

Backyard suite

A separate home in the yard of a house: garden suite, laneway suite or coach house, including prefab, modular or container units used this way.

Allowed · Sarnia’s term: “detached additional dwelling unit (ADU)”

The City's Building Services takes building permit applications for new detached additional dwelling units, including converted detached garages. The posted zoning by-law text has no detached-ADU standards, so the general accessory building rules are the closest written limits (see notes). Ontario's Planning Act (s. 35.1) overrides zoning provisions that would prohibit one unit in a building ancillary to a house on serviced urban land. [1][2]

Servicing: A septic assessment may be required for properties on septic (County of Lambton building services) [3]
Maximum height: Accessory buildings in Residential zones: 1 storey and 5.0 m (3.5 m with a flat roof) (s. 3.1(2)(d)). Not confirmed to be the standard applied to detached ADUs. [4]
Approvals: A building permit is required to create an additional dwelling unit, even if no construction is proposed; the unit cannot be occupied until it passes an occupancy inspection [3]

Ontario-wide rule

Ontario law stops municipalities from banning one residential unit in a building ancillary to a detached house, semi-detached house or rowhouse on a parcel of urban residential land, as long as the lot has no more than three units in total. Municipalities still set most other zoning rules, but provincial law limits parking requirements, minimum unit size, lot coverage and separation distances. These units are also exempt from development charges and parkland dedication. [2][5][6]

Tiny home on a foundation

A small house as the main home on its own lot. The key rule is any minimum dwelling size.

Allowed · Sarnia’s term: “single detached dwelling”

The general regulations and the residential and rural zone sections read set no minimum floor area for single detached dwellings. Some site-specific exceptions do, e.g. UR1-49 and UR1-50 require at least 158 m². [7][8]

Minimum dwelling size: No general minimum. Site-specific UR1-49 and UR1-50: 158 m² (185 m² for two-storey in UR1-50) [9]

Ontario-wide rule

Ontario law sets no minimum total size for a house that is the main dwelling. The Building Code sets minimum room areas, so the smallest compliant dwelling is roughly 17.5 m² by the Province's own estimate. Municipalities may still set minimum floor areas for main dwellings in their zoning by-laws. The provincial ban on minimum sizes covers only additional residential units. [2][10][11][12][13][14][15]

Tiny home on wheels or park model

Living full-time in a tiny home on wheels or a park model home.

Allowed with limits · Sarnia’s term: “mobile home / park model home”

Using a travel trailer, tent trailer or motor home as a dwelling unit is prohibited in all zones. Mobile homes and park model homes are permitted in the Private Residential Community 1 (PRC1) zone. [16]

Where allowed: PRC1 zone permits mobile homes, modular homes and park model homes on community lots of at least 300 m² (s. 13.1, 13.2.2) [17]
Temporary garden suite: Council may pass temporary use by-laws under Planning Act s. 39, for up to 10 years for a garden suite (s. 3.46). Section 38 (Temporary Use Zone) shows site-specific temporary garden suites, e.g. UR2-T1. [4]
Approvals: s. 3.49(1) prohibits use of a travel trailer, tent trailer or motor home as a dwelling unit [4]

Ontario-wide rule

Ontario has no single rule for living full-time in a tiny home on wheels. A unit on wheels can count as a 'building' that needs a permit and must meet the Building Code once it stays in one place, is hooked up to services or is anchored. Park model trailers are recognized only as seasonal recreational buildings. Municipalities may allow a portable garden suite under a temporary-use by-law for up to 20 years, with extensions of up to 3 years each. [15][10][2][12][11]

Bunkie or sleeping cabin

A small sleeping building with no kitchen, usually beside a cottage or house.

Not addressed · Sarnia’s term: “accessory building”

The by-law does not mention bunkies or sleeping cabins. General accessory building rules apply, and s. 3.1(2)(k) says no accessory building may be used as a dwelling unit.

Maximum size: Accessory buildings in RR1 and RU1 zones: 5% maximum combined lot coverage (s. 3.1(3)(d)); other Residential zones: 10% (s. 3.1(2)(f)) [4]

Ontario-wide rule

Ontario law has no rule written specifically for bunkies or sleeping cabins. Whether one needs a building permit depends on the Building Code Act's definition of 'building' and the Code's shed exemption. That exemption covers only storage-use sheds, so it does not cover a structure used for sleeping. Municipal zoning rules for accessory buildings still apply. [12][10][2][18]

Official links

Last confirmed October 2026.

Notes and caveats

The by-law is posted as separate section PDFs with no overall consolidation date; the latest amendment cited in Sections 2–3 is By-law 49/2025. Conflict: s. 3.1(1) and 3.1(2)(k) of the posted text still say no accessory building may be used as a dwelling unit, and s. 3.10(4) only allows a 'secondary dwelling unit' inside the main dwelling (minimum 35 m²). The City's ADU page and 'New Detached ADU' building permit package (uploaded 2026-09) still accept detached ADUs, presumably under the Planning Act's provincial permission for additional units (Bill 23), so the zoning standards for detached ADUs (size, setbacks) could not be confirmed. A new comprehensive zoning by-law (final draft) went to a special Council meeting on 2026-05-11; the Speak Up Sarnia page and a web search found no evidence it has been passed, and the City still presents By-law 85 of 2002 as current. If passed, these answers may change. Sections read: 01, 02, 03, 05 (RU1), 06 (RR1), 07 (UR1), 08 (UR2), 12 (SR1), 13 (PRC1), 34 (W1), 38 (T).

Sources

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Sarnia zoning for small homes

Backyard suite

Ontario-wide rule

Tiny home on a foundation

Ontario-wide rule

Tiny home on wheels or park model

Ontario-wide rule

Bunkie or sleeping cabin

Ontario-wide rule

Official links

Sources

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