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Modular Homes & Garden Suites in St. Catharines, Ontario
Factory-direct modular homes and backyard suites for St. Catharines and the Niagara Region. Here's what St. Catharines's accessory-dwelling-unit by-law allows in your backyard, what it costs, and the rules that apply.
What you can build in St. Catharines
Full modular homes — from $175,696. 29 models from 560 to 1,405 sq ft, 1–3 bedrooms — factory-built to the Ontario Building Code and set on a permanent foundation (a real, permanent house, not a “trailer”).
Backyard suites (ADUs) — from $96,244. 7 compact models built for garden-suite and in-law-suite use, sized to fit what St. Catharines's by-law allows.
All homes are CSA-certified (A277 modular / Z240MH manufactured), finished in the factory, and delivered ready for foundation and hook-up. What's the difference between modular, manufactured, and mobile? →
Find your backyard suite — 3 quick questions
We'll narrow the models that fit a typical St. Catharines backyard allowance to the ones that fit your life. No email needed.
1 · Who's it for?
2 · What layout?
3 · What size feels right? (St. Catharines lots typically allow up to ~860 sq ft)
St. Catharines caps a detached suite at 80 m² (≈860 sq ft); on smaller lots the 10% accessory-coverage limit often binds first. Your exact lot may allow more or less — get the real number for your address in seconds.
Check your exact St. Catharines address →Can you put a garden suite (ADU) in your St. Catharines backyard?
Often, yes — St. Catharines permits a detached Additional Residential Unit on most serviced residential lots. The specifics, from City of St. Catharines Zoning By-law 2013-283 s.2.2.1 (added by By-law 2024-032, April 2024):
| Max size | 80 m² (≈860 sq ft). On smaller lots the 10% accessory-building lot-coverage cap (all accessory structures combined) often binds first. |
|---|---|
| Max height | 4.5 m (≈15 ft) to the top of walls, up to 6.0 m (≈20 ft) to a gable/dormer peak |
| Setbacks | 1.2 m (≈4 ft) rear & side · 3.0 m (≈10 ft) separation from the main house. Not permitted in the front yard. |
| Units per lot | Up to 2 ADUs (both may be detached, or one inside + one detached). Also permitted in the agricultural zones where Section 13 allows. |
| Parking | 0.5 space per ADU (tandem permitted) — one space can cover two ADUs |
| Servicing | Municipal water & sewer |
| Conservation | Niagara Peninsula Conservation Authority (NPCA) on floodplain / watercourse / hazard lands |
Getting your building permit in St. Catharines
An eligible lot still needs a building permit before anything is delivered. Here's how St. Catharines's process actually works — verified against the St. Catharines building department's own pages.
How do you apply for an ADU building permit in St. Catharines?
Through BuildSTC (the City's online permit portal) (application portal ↗). Apply online through BuildSTC (residential new construction, additions, secondary suites), or by mail, the 24/7 City Hall drop box, or in person — residential applications need the permit form plus two complete sets of construction drawings. St. Catharines's building-permit page ↗
- Confirm zoning for the detached unit (size, height, setbacks, and the 0.5-parking-space-per-ADU minimum) — even the City's pre-approved designs don't cover site layout
- Assemble the package: the permit application form, two sets of construction drawings — or one of the City's pre-approved detached ADU design sets — and a site plan with dimensions and setbacks
- Submit through BuildSTC (or mail, drop box, or in person)
- The City reviews against the Building Code and Zoning By-law — the 10-day clock starts once staff confirm the submission is complete
- Pay the permit fee and any deposits, and the Chief Building Official issues the permit
- Book inspections through the portal as construction proceeds, ending with the final inspection
What does a St. Catharines ADU permit application need?
- Building Permit Application form
- Two complete sets of construction drawings — or the City's pre-approved detached ADU design set
- Site plan showing the unit's dimensions and setbacks
- For a factory-built ADU: the manufacturer's CSA-certified drawings and specifications alongside the site-specific drawings
- Proof of ownership / applicant authorization where applicable
How much does an ADU building permit cost in St. Catharines?
St. Catharines sets permit fees in its Rates and Fees Guide, but a current ADU figure couldn't be verified during the City's ongoing website migration — get an estimate from Planning and Building Services before budgeting. The bigger number to know: the ADU Community Improvement Plan grant covers up to 70% of costs to $80,000 for a detached unit (when an intake is open).
| Permit fee | Set in the City's Rates and Fees Guide — confirm the current residential rate with Planning and Building Services (905-688-5600) |
|---|---|
| ADU CIP grant (incentive, not a fee) | Up to 70% of eligible costs — max $40,000 interior / $80,000 detached, $80,000 combined per property; Urban Area CIPA properties only, intake-dependent |
How long does an ADU building permit take in St. Catharines?
Ontario's Building Code requires a decision on a complete house-class application within 10 business days. The City is explicit that the mandated review timeline starts only after staff confirm the application is complete.
Worth knowing before you apply
- St. Catharines publishes pre-approved detached ADU designs (including manufacturer models around 37–80 m²) that are Building-Code pre-reviewed — but the City is explicit they do NOT cover zoning/site layout, which is confirmed at permit stage
- The ADU CIP grant is Urban Area CIPA properties only, and the intake was reported CLOSED as of April 2026 pending new funding — verify current status at stcatharines.ca/CIP before counting on it
- Grant costs only qualify if incurred AFTER permit issuance, the grant application is due within 90 days of the permit, and the project must finish within 12 months — all hard deadlines
- Property-tax or City-charge arrears disqualify the grant, and a compliance audit precedes payment
- Lots near a watercourse, wetland, or floodplain may need Niagara Peninsula Conservation Authority review on top of the building permit
Fees and timelines are estimates from St. Catharines's published schedules, verified July 4, 2026. Rates and processes change — always confirm current requirements with the building department before you apply.
Grants & financing in St. Catharines
St. Catharines CIP ADU Grant — Up to 70% of costs (max ~$80,000 for a detached ADU) for properties in the Urban Area Community Improvement Plan — an incentive, not a requirement.
See every program → Ontario ADU Grants Directory
A modular or prefab home on a permanent foundation is financed like any house. CMHC Prefab Plus allows an insured mortgage with as little as 5% down on the first $500,000, with construction funds released in stages. How modular home financing works →
Thinking of the suite as a rental? Run the numbers →
St. Catharines modular homes — FAQ
Can you put a garden suite in St. Catharines?
Yes. St. Catharines permits up to two accessory dwelling units per lot (with a detached, semi, or townhouse dwelling) — subject to the size, height, and setback rules and a building permit.
How big can a garden suite be in St. Catharines?
Up to 80 m² (≈860 sq ft), though on smaller lots the 10% accessory-coverage cap often binds first. Check your address for the exact number.
Can you put a modular home in St. Catharines?
Yes. On land you own, a modular home on a permanent foundation is legal residential housing under the Ontario Building Code throughout St. Catharines, subject to standard zoning and permits.
How much does a modular home or backyard suite cost in St. Catharines?
Modular home models start at $175,696 and run to about $338,000 for the largest layouts; backyard ADU models start at $96,244. Site work, foundation, delivery, and permits are additional.
Can I get a mortgage on a modular home in St. Catharines?
Yes — on a permanent foundation it is financed as real property, including via CMHC Prefab Plus (5% down on the first $500,000).
Local rules summarized from City of St. Catharines Zoning By-law 2013-283 s.2.2.1 (added by By-law 2024-032, April 2024); verified by Modular Homes 400 and reviewed by James Clarke, REALTOR®. Always confirm current requirements with the City of St. Catharines before you build.