Garden Suites in Durham Region: Oshawa to Clarington, Checked
Oshawa, Whitby, Ajax, Pickering and Clarington all allow a unit in a detached building on a serviced urban lot. Whitby and Pickering share a catalogue of pre-reviewed designs and Whitby will refund fees until December 31, 2026. Oshawa caps a backyard unit at 60 m² and 4.5 m tall.
At a glance
Whitby’s refund needs a complete permit application by December 31, 2026 and registration by March 31, 2027. The Town says there will be no extensions.
Yes, on most Durham house lots with municipal water and sewer. In Oshawa the backyard unit is limited to the smallest of 8% of the lot, 50% of the house’s coverage, or 60 m², and 14 ft 9 in tall. Whitby charges $268 to register and refunds permit fees and school board charges on detached ADUs if your complete application is in by December 31, 2026. Whitby and Pickering share six pre-reviewed designs.
We Don’t Build in Durham. We just hate watching money get wasted.
We are a builder based in Tiny Township. We build garden suites in Simcoe County and around Georgian Bay through ICFhome.ca. Outside Simcoe, we sell lot reports, permit packages and builder calls. We are not quoting your Whitby backyard.
We have built 300+ custom homes since 1979. The bad garden suite projects we hear about rarely fail on the building. They fail on a sewer that runs the wrong way, a parking space that doesn’t fit, or a deadline that passed while the drawings sat on someone’s desk. Durham has one of those deadlines coming up.
What each town calls it
- Oshawa: “accessory apartment” and “accessory dwelling”; a property with one is a registered “two-unit house”.
- Whitby: “Additional Dwelling Unit” (ADU), with “detached ADU” for the backyard.
- Pickering: “Additional Dwelling Unit”, same as Whitby.
- Ajax: “Additional Residential Unit” is the provincial term; confirm the Town’s wording with Building Services.
- Clarington: “additional dwelling unit” in its Official Plan, and “garden suite” for a temporary unit on rural land.
Durham Garden Suite Rules compared
What each town publishes for a unit in a detached building. Where a number is not published on the town’s own pages, we say so. We would rather leave a blank than send you to a designer with a wrong number.
| Town | Max size | Max height | Setbacks | Parking | Fees / registration |
|---|---|---|---|---|---|
| Oshawa | Smallest of 8% of lot, 50% of house coverage, or 60 m² ground floor | 14 ft 9 in (about 4.5 m) to peak, most cases | 2 ft (about 0.6 m) most cases; not in front yard | 2 for house + 1 per accessory unit | Permit per By-law 33-2009; registration automatic with permit |
| Whitby | 75 m² GFA; one ADU per accessory structure (By-laws 8141-24 and 8143-24) | 4.5 m in Residential zones (8141-24); 5.5 m in other zones and under By-law 5581-05 (8143-24) | 1.2 m interior side and rear; 3.0 m exterior side. ADU structure excluded from lot coverage | Not published — check by-law | Registration $268; fees refundable under HAF |
| Pickering | Not published — check zoning | Not published | Not published | Not published | Not published — check with Building Services |
| Ajax | Not verified — check with the Town | Not verified | Not verified | Not verified | Not verified |
| Clarington | Smaller than the main house floor area | 5.25 m in Urban Residential zones; 6.5 m in Agricultural or Rural Residential zones | Zone front and exterior side yards; 1.8 m rear and interior side. Accessory building max 10% of lot or zone coverage, whichever is less | Not published | Registration required (OP policy 6.3.9) |
Last checked October 2026 · Sources: Oshawa Accessory Apartments, Whitby ADUs, Pickering pre-approved designs, Clarington OPA 129
What You Can Build in each town
Oshawa: small, low, and clearly written
Oshawa’s accessory apartments page is one of the plainest in Ontario, which we appreciate. On urban lots zoned R1 to R5 with municipal water and sanitary sewer, you can have up to three units, with no more than one in an accessory building.
- Size: the most restrictive of 8% of the lot area, 50% of the house’s lot coverage, or 60 m² (646 sq ft) of ground floor area.
- Height: roof peak no higher than 14 ft 9 in from grade, in most cases. That is a one-storey building.
- Setbacks: 2 ft in most cases. Not in the front yard, or the minimum exterior side yard on a corner lot.
- Parking: 2 spaces for the house, plus 1 per accessory unit, each 2.75 m by 5.75 m. With two units, at least two spaces need clear street access (no tandem).
- Landscaping: at least 50% of the front yard and exterior side yard stays landscaped open space.
Do the 8% math early. On a 450 m² lot, 8% is 36 m². That is a studio, not a one-bedroom. If your house only covers 100 m², the 50% rule caps you at 50 m² no matter how big the lot is.
Lots without municipal services can only add a unit inside the house, not in an accessory building, and only with at least 11 m of frontage (Section 5.12 of Zoning By-law 60-94). Check CLOCA regulated areas and MTO controlled areas before you design.
Whitby: the deadline town
Whitby allows ADUs in certain single detached and semi-detached homes, under zoning amendments 8141-24, 8142-24 and 8143-24. The Town’s ADU page sends you to a Planning Inquiry to confirm your lot, and it does not publish the detached size and height limits. Ask for them in writing.
What Whitby does publish is money:
- Registration: $268. If the unit is discovered through a complaint: $534. Transfer to a new owner: $107.
- Development charges do not apply to an ADU that meets O. Reg. 454/19. Education development charges from both school boards do apply to every detached ADU.
- Under the Housing Accelerator Fund incentive, Whitby will reimburse the ADU building permit fee, registration inspection fee, curb cut fee, below-grade entrance fee and the education development charges on detached ADUs. Minor variance fees are not covered.
Whitby’s registration by-law is 8156-25. The Town runs a fire inspection only for ADUs that existed before July 14, 1994; new units go through building permit inspections, an ESA or licensed electrical contractor certificate, and an exterior inspection by Enforcement Services.
Pickering: shares Whitby’s design catalogue
On November 20, 2025, Pickering announced pre-approved detached ADU designs pre-reviewed by both cities under the Building Code. The designs use heat pump HVAC and are built to higher snow loads. You still apply for a building permit, and it is checked against your lot’s zoning and site conditions. Pickering’s own size, height and setback limits for a detached unit are in its zoning by-law; its announcement does not list them.
Ajax: ask before you assume
We could not verify Ajax’s detached-unit numbers from the Town’s website for this update. The provincial floor applies: on a serviced urban lot, up to three units including one in a detached building. Everything else, from height to parking, comes from the Ajax zoning by-law. Email the Town’s Building Services with your address and get the limits in writing before you pay for drawings.
Clarington: town lots, moraine lots and garden suites
Clarington covers Bowmanville, Courtice and Newcastle, plus a lot of countryside on the Oak Ridges Moraine and in the Greenbelt. That is why its rules split. Its Official Plan amendment, OPA 129, says:
- A unit is allowed in a detached accessory building on the same lot, and the building must be “secondary in size and scale” to the house. It cannot be severed.
- On the Oak Ridges Moraine (Prime Agricultural, Rural and Hamlet), one additional unit only, and only inside a single detached house. None in Natural Core or Natural Linkage areas.
- In the Greenbelt Protected Countryside, one additional unit, inside the house or an accessory building that existed (or had a permit) before July 1, 2017.
- No additional units on hazard lands, including the Lake Ontario regulatory shoreline.
- Units must be registered with the Municipality.
OPA 129 was written in 2021 to implement the earlier Bill 108 rules. Bill 23 later raised the provincial floor on serviced urban lots to three units, so check Clarington’s current zoning for urban numbers. For a rural lot, Clarington also has garden suite criteria in the same policy, including adequate water supply and sewage disposal. That is a temporary-use permission, not a permanent unit. Our temporary garden suite guide explains how those work.
The Whitby and Pickering Catalogue: what you get, what you don’t
The Whitby and Pickering ADU Regional Design Catalogue lists six detached designs: five from three local design firms and one from CMHC’s national Housing Design Catalogue.
| Design | Size | Layout | Source |
|---|---|---|---|
| Model 20 (peaked roof) | 264 sq ft | 1 bed, 1 bath | Local designer |
| ADU Model 8-2 | 409 sq ft | Studio, 1 bath | Local designer |
| Floor plan 230024 | 450 sq ft | 1 bed, 1 bath | Local designer |
| ADU Model 9-4 | 473 sq ft | 1 bed, 1 bath | Local designer |
| Model 30A (flat roof) | 484 sq ft | 1 bed, 1 bath | Local designer |
| Accessory Dwelling Unit 01 | 634 sq ft | 1 bed, 1 bath | CMHC Housing Design Catalogue |
Last checked October 2026 · Source: Whitby and Pickering ADU Regional Design Catalogue
You buy the design from the designer, not the town, and the catalogue does not publish prices. The page says the purchase includes “applicable foundation and HVAC plans” and that you contact the designer for a site plan. The Town asks that you do not alter the design.
Here is what a pre-reviewed design does not do for you: it doesn’t check your zoning, place the building on your survey, design the grading so your neighbour’s yard stays dry, route the sewer and water from the house, or size your electrical service. Those are the parts that go wrong. Note that a 634 sq ft design will not fit under Oshawa’s 60 m² footprint cap either, so don’t assume the catalogue travels across the town line.
Development Charges, Incentives and deadlines
Development charges. Ontario’s Development Charges Act exempts a second unit in an ancillary building where the main house has no more than two units. Whitby states it plainly: DCs do not apply to an ADU that meets O. Reg. 454/19, but education development charges apply to every detached ADU. Assume the same pattern in the other four towns and confirm on your permit invoice. More detail on our development charges page.
Whitby’s fee refund is the one to plan around. Read the conditions carefully, because the Town says there are no exceptions or extensions:
Permit issued on or after April 1, 2024
Your ADU building permit must fall inside the program window, and you must be the registered owner.
Complete application by December 31, 2026
Not started, complete. Whitby suggests submitting at least two weeks early. Any minor variance must already be final and binding.
All fees paid
You pay first and get reimbursed. One incentive application per ADU permit.
Register and sign by March 31, 2027
Register the ADU with By-law Services and return the signed Incentive Agreement. Miss it and you repay the incentive by April 30, 2027.
| Town | DC on qualifying detached unit | Incentive | Deadline | Pre-approved plans |
|---|---|---|---|---|
| Oshawa | Provincial exemption — confirm | None found | — | No (City says hire a qualified designer) |
| Whitby | Exempt (O. Reg. 454/19); education DCs apply but are refundable under HAF | HAF fee reimbursement | Complete permit app Dec 31, 2026; registration Mar 31, 2027 | Yes, shared catalogue (6 designs) |
| Pickering | Provincial exemption — confirm | None found for owners | — | Yes, shared catalogue |
| Ajax | Provincial exemption — confirm | Not verified | — | Not verified |
| Clarington | Provincial exemption — confirm | Not verified | — | Not verified |
Last checked October 2026 · Sources: Whitby ADUs and HAF incentive, Oshawa Accessory Apartments
Racing Whitby’s December 31 deadline?
Our Urban Pre-Approved Wrapper takes a catalogue design and adds the site plan, grading coordination, forms and heat loss you still need. From $1,499.99 + HST, fixed quote first.
Durham’s Pipes Belong to the Region
In Durham, water and sewer are run by the Regional Municipality, not your town. Your town issues the building permit; the Region owns the pipe in the street. That is why Oshawa notes that curb cuts on regional roads need Durham Region’s approval, not the City’s.
- No services, no backyard unit. Oshawa only allows an accessory building unit where there is municipal water and sanitary sewer. Rural Clarington and north Pickering lots on wells and septic are a different process entirely.
- Lateral depth decides the floor height. If the house drain is shallow and the suite is at the back of a deep lot, gravity may not work. A sewage pump is a real cost and a real maintenance item.
- Shoreline and moraine. Lake Ontario shoreline lots in Pickering, Ajax, Whitby and Clarington can be hazard land. Clarington bans additional units on hazard lands outright. Check with CLOCA or TRCA early.
- Electrical service. A heat pump suite out back plus a house on a 100 amp service usually means an upgrade. Price it before you sign anything.
If your rural lot qualifies for a temporary garden suite on private services, septic design has to come from a qualified designer; we send that to SepticReplacement.ca. For the stamped heat loss and HVAC design every permit wants, see OntarioHeatLoss.ca.
Common Mistakes in Durham
Missing the Whitby window by a week
“Submitted” is not “complete”. If the Town sends your application back for a missing heat loss on December 29, you may be out.
Treating the catalogue as a permit
A pre-reviewed design still needs a site plan, grading and servicing for your lot. Those are where the surprises live.
Using a Whitby design in Oshawa
Oshawa’s 60 m² and 14 ft 9 in caps rule out some catalogue designs. Check the numbers before you buy plans.
Forgetting school board charges
Whitby charges education DCs on every detached ADU. Outside Whitby’s refund program, budget for them.
Parking that blocks itself
Oshawa wants spaces with clear street access, not tandem, once you have two or three units. A single-car driveway rarely works.
Building on the moraine like it is a subdivision
Clarington’s Oak Ridges Moraine and Greenbelt policies are much tighter than its town rules. Find your designation first.
Rules of thumb before you spend a dollar
- Get your town’s detached-unit numbers in writing for your address.
- Do Oshawa’s three-way size math (8% / 50% / 60 m²) even if you are not in Oshawa. It is a good reality check.
- If you are in Whitby, work backwards from December 31, 2026 and leave a month of slack.
- Ask for the sewer lateral depth and water service size before you place the building.
- Price the site work before the building. Our servicing cost guide shows where it goes.
Find out if your Durham lot works, in 48 hours.
Our $399 + HST Garden Suite Feasibility Report checks zoning, size, height, servicing and conservation authority flags for your address. The fee is credited toward permit plans.
Durham Garden Suite FAQ
How big can a garden suite be in Oshawa?
Oshawa limits a unit in an accessory building to the most restrictive of 8% of the lot area, 50% of the house’s lot coverage, or 60 m2 of ground floor area. The roof peak can be no higher than 14 ft 9 in from grade in most cases, with setbacks of 2 ft in most cases.
What is the Whitby ADU incentive deadline?
Your complete building permit application must be submitted by December 31, 2026, and the ADU must be registered and the incentive agreement signed by March 31, 2027. The permit must have been issued on or after April 1, 2024. Whitby says there will be no exceptions or extensions.
What fees does Whitby refund for a detached ADU?
Under its Housing Accelerator Fund incentive, Whitby reimburses the ADU building permit fee, registration inspection fee, curb cut fee, below-grade entrance fee and education development charges on detached ADUs, where they apply. Minor variance fees are not eligible.
Are there pre-approved garden suite plans in Durham?
Yes, in Whitby and Pickering. Their shared ADU Regional Design Catalogue lists six detached designs from 264 to 634 sq ft, five from local designers and one from CMHC. You buy from the designer, and the purchase includes foundation and HVAC plans. You still need a site plan and a permit.
Do I pay development charges on a garden suite in Durham?
Municipal and regional development charges are generally exempt for a qualifying second unit in an ancillary building. Whitby confirms this and notes education development charges still apply to all detached ADUs. Confirm the full permit invoice with your town.
Do I have to register a garden suite in Oshawa or Whitby?
In Oshawa, completing the building permit automatically registers the property as a two-unit house, and the certificate arrives within 60 days of the permit being closed. Whitby charges $268 to register, $534 if the unit is found through a complaint, and $107 to transfer the registration.
Can I build a garden suite on a rural Clarington lot?
Possibly, but not under the same rules as town lots. On the Oak Ridges Moraine the Official Plan allows one additional unit only inside a single detached house, and none in Natural Core or Linkage areas. Clarington also has garden suite criteria for temporary units, which require adequate water supply and sewage disposal. Talk to Clarington planning first.
What are the garden suite rules in Ajax?
We could not verify Ajax’s detached-unit limits from the Town’s website for this October 2026 update. Provincial law allows up to three units on a serviced urban lot, including one in a detached building. Ask Ajax Building Services for the zoning limits for your address in writing.
Will you build my garden suite in Durham Region?
No. We build in Simcoe County and around Georgian Bay. In Durham we sell the $399 + HST feasibility report, permit packages and paid builder calls, so you can hire a local builder with a checked lot and a clear scope.