Cornwall: questions buyers ask
What records explain additional residential units at a Cornwall home?
Section 3.4 of the City's Zoning By-law 2022-001, in the December 2025 office consolidation, and the City's building permit page.
Sources checked October 29, 2026
The rule in Cornwall
Up to 3 homes on a lot
Cornwall zoning by-law 2022-001 s.3.4: permits up to three dwelling units on a serviced lot with a single detached, semi-detached, duplex, link or row house (three in the house, or two in the house and one in an ancillary building; up to four in a semi-detached house with none in an ancillary building), each with one parking space; no basement unit in the floodplain or natural heritage zones.
From Cornwall by-law 2022-001 s.3.4, checked 29 Oct 2026
- The recordAdditional residential units
- Where to read itZoning; Zoning By-law 2022-001, December 2025 office consolidation and 1 more
- The free check reads itPick “Extra units allowed”
What the record shows
Section 3.4 of Zoning By-law 2022-001 says that where public or private water and sewer services are available, a single detached, semi-detached, duplex, link-detached or row house may hold one or two dwelling units if its ancillary buildings hold no more than one unit between them, or three units if no ancillary building holds one; an ancillary building may hold one unit if the house holds no more than two. A semi-detached house may hold up to four units if no ancillary building holds any. An additional unit's floor area may not exceed the main home's, lot occupancy is capped at 45% unless the zone allows more, each unit needs one parking space (tandem parking with the main home's space is allowed) and no new driveway may serve the unit alone.
A unit in an ancillary building needs a rear yard of at least 3 metres, may sit no closer to the street than the main building, and a garage that holds one is limited to a 60 m² footprint; no unit may be added where a garden suite exists. A basement unit is not permitted in the Environmental Constraint Floodplain or Natural Heritage zones, or on the lands the by-law lists as subject to flooding. The City's building permit page lists installing an accessory apartment among the work that needs a permit. A permission in the zone does not make an existing basement apartment lawful; the building permit and its inspections are the records that do.
Where to read it yourself
- Zoning: the City's zoning page, with the interactive zoning map and the by-law's sections
- Zoning By-law 2022-001, December 2025 office consolidation: section 3.4, ancillary residential uses (PDF)
- Building Permits: the City's page on work that needs a permit, an accessory apartment included
What OfferDue covers in Cornwall
Extra units allowed is in the free check as a summary of the City's rule, from our hand-kept table of city rules, and the full report reads the lot's zone where the City's zoning map is open data we can use; where it isn't, the report's line says where the City publishes it. Neither is confirmation that a particular unit holds a permit or may be occupied.
Free check: pick “Extra units allowed” See the sample report
Public-record information, not legal, financial, insurance or inspection advice. Records change and can be incomplete, and this page describes the records, not any particular home. What we cover, city by city.