How Much Does a Prefab Garden Suite Cost in Ontario?

Most prefab and modular garden suites in Ontario cost between $225,000 and $380,000 all-in in 2026 — the factory-built structure plus everything the site needs: foundation, servicing trenched from the main house, delivery and placement, connections, and permits. Advertised factory prices are usually much lower because they cover only the building itself. The honest comparison is always the complete, occupied suite on your lot, which is why we quote prefab projects all-in the same way we quote custom ones.

Factory price lists typically cover the structure: panels or modules, windows, and interior finishes to some specification. What they exclude is everything that turns a building into a legal dwelling on your specific lot — design adaptation and permit drawings, the permit itself, excavation and foundation, water, sewer, and hydro trenched from the main house, crane or delivery logistics, connections, decks and steps, and landscaping repair. Those site costs commonly add $80,000 to $150,000 to a factory price, which is why all-in quotes are the only ones worth comparing.

Usually, yes — prefab suites start around $225,000 all-in versus roughly $285,000 for a comparable custom build, and the factory schedule compresses on-site construction to about 10 to 16 weeks. The savings come from factory efficiency and repeated, refined designs. The trade-off is flexibility: prefab works best when a standard plan suits your lot and needs. Awkward lots, tight access that a module cannot navigate, or specific layout needs (like a fully accessible in-law suite) often favour custom. A feasibility review tells you which path fits your property.

Yes — exactly the same permits as a custom build. A prefab suite is a dwelling, so it needs a building permit, zoning compliance (Toronto's 60 m² limit, setbacks, angular planes, emergency access, and tree protection all apply), staged inspections, and occupancy sign-off. Permits typically take 2 to 4 months. The factory schedule does not shorten the approval stage — it shortens construction after the permit is issued, which is where the prefab timeline advantage really lives.

Once permits are issued, on-site work typically runs 10 to 16 weeks: foundation and servicing first, then delivery and placement of the structure, then connections, finishing, and inspections. Add the 2 to 4 month permit stage up front and a prefab project commonly lands around 5 to 8 months end to end — a meaningful saving versus the 6 to 10 months of a custom build, and with less on-site disruption for you and your neighbours.

Yes, with the same tools as any garden suite: since 2025, insured-mortgage rules let qualifying homeowners refinance up to 90% of their property's as-improved value specifically to add a secondary suite, a HELOC or conventional refinance typically covers the balance, the Multigenerational Home Renovation Tax Credit can return up to $7,500 for qualifying family builds, and development charges are waived for additional residential units in most municipalities. Lenders will want a fixed-price contract for a permitted project — which an all-in prefab quote provides. Confirm current program terms before budgeting.