Short answer: every municipality regulates a detached backyard unit with the same eight measurements — rear setback, side setback, separation from the house, height, floor area, lot coverage, the access path, and parking — and every one sets them to different numbers. The province fixes a floor for two of them (4 m separation unless the by-law allows less; 45% coverage must be permitted). The rest is local. This guide explains each rule once, then puts the GTA municipalities we build in side by side, with a source for every figure in the table and a separate list of the figures we could not source.
The eight rules, and what each one is actually for
1. Rear setback. The minimum distance from the suite's rear wall to the rear lot line. Protects the neighbour behind you — their light, their privacy, their drainage. Ranges across the GTA from 0.6 m (Ajax, Oshawa, Whitby's general accessory rule) to 2.5 m (Brampton). Several cities increase it with height: Toronto adds 1.5 m where rear windows sit above 4.0 m and the rear lot is residential; Burlington's rises to 3 m for the portion of the building above 4.6 m (peaked roof) or 3.5 m (flat).
2. Side setback. Same idea, to the side lot lines. Often conditional on openings — a blank wall can sit closer than a wall with windows — and on whether the side abuts a street. Toronto's garden-suite side setback is the greater of 1.5 m or a share of lot frontage to a published maximum; Markham allows 0.5 m with a blank wall on lots under 4,000 m²; Oakville requires 1.2 m from an interior side or rear line and 3.5 m from a flankage line.
3. Separation from the main house. The distance between the suite's main wall and the house's main wall. This is the rule the province intervened on: O. Reg. 299/19, as amended by 462/24, says the unit "shall be at least 4 metres from another building or structure on the parcel if the other building or structure contains a residential unit," and a by-law permitting less prevails (O. Reg. 299/19 s. 4). That is why Toronto's laneway separation dropped to 4.0 m in July 2025 (By-law 847-2025). Cities may still require more for taller suites — Toronto requires 7.5 m for a suite taller than 4.0 m (By-law 849-2025) — and several require less: 3 m in Brampton, Ajax, Caledon and Oshawa; Oakville uses 2.0 m as the threshold below which the suite takes the main building's yards.
4. Height. Usually measured to the ridge or to the main-wall top, often with two tiers: one height close to the house, a taller one further away. Toronto: 4.0 m within 7.5 m of the house, 6.3 m beyond (By-law 849-2025). Burlington distinguishes roof shapes: 7 m for a peaked roof, 6 m for a flat one (Burlington By-law 09-2026 handout). Richmond Hill allows two storeys and 7.5 m overall (By-law 143-24). A one-storey suite with a low-slope roof fits almost everywhere; a two-storey suite fits in a minority of cities and only on larger lots.
5. Floor area. The cap on how big the suite can be, sometimes absolute, sometimes a formula. This is where the cities diverge most: 15 m² for a permanent detached unit on a Markham lot of 500 m² or less — the general accessory-building limit, which is what governs after By-law 2026-44 deleted the old garden-home standard (Markham By-law 2024-19, s. 4.8.1.2(b)); 35 m² in most Brampton zones (Brampton garden suites); 80 m² in Burlington, Richmond Hill and Caledon's R1 group; 120 m² in Toronto, or 60 m² for one storey, and always less than the house (By-law 849-2025). Several cities also cap it as a fraction of the house — Caledon's R1-group cap is 80 m² and not more than the main dwelling's ground floor (By-law 2006-50 s. 6.4).
6. Lot coverage. The share of the lot all buildings together may cover. The province says "up to 45 per cent of the surface of the parcel is permitted to be covered by buildings and structures" (O. Reg. 299/19 s. 5). Toronto applies 45% for all buildings, or excludes the garden suite and limits ancillary buildings to 20% (Chapter 150.7); for a laneway suite, the building is excluded from the overall calculation but all ancillary buildings combined "may not exceed 30 percent of the lot area" (Chapter 150.8.60.70). Oshawa stacks three tests — 8% of lot, 50% of the house's coverage, 60 m² of ground floor — and applies the most restrictive (Oshawa accessory apartments). Oakville caps the detached unit itself at the greater of 5% of the lot or 42 m² (Oakville By-law 2014-014 Part 6, Table 6.5.3). Richmond Hill excludes the accessory residential building from the coverage calculation entirely (By-law 143-24 s. 3(t)).
7. The access path. A clear route from the street to the suite's door, with a minimum width, a minimum height, and in most cities a maximum length. This is a fire and emergency requirement applied through the Building Code, and it is rarely a variance item. Width ranges from 0.81 m (Oshawa) through 0.9–1.0 m (Toronto, Richmond Hill) to 1.2 m (Mississauga, Brampton, Vaughan, Ajax, Caledon). Toronto's published options for a garden suite are 45 m from the public street to the entry, or 90 m "along with at least one additional fire-safety measure, acceptable to the City of Toronto" — a sprinkler with an exterior strobe and interconnected alarms, or increased fire-protection materials with the same strobe and alarms — on a path at least 1.0 m wide by 2.1 m high (0.9 m if sprinklered); and "a fire hydrant must also be located within 45 metres of where a firefighting vehicle would park" (Toronto fire department access to a new garden suite). For a laneway suite the path is 0.9 m × 2.1 m, the 90 m option may run through the laneway, and the hydrant rule is the same (fire department access to a new laneway suite). Mississauga caps its 1.2 m × 2.1 m route at 45 m (Mississauga additional residential units). Richmond Hill also caps at 45 m (site plan guide).
8. Parking. Whether the suite needs its own space. Burlington and Ajax require none for the first unit; Oshawa requires one per unit on top of the house's; Caledon waives it near transit. Oshawa's rule that three units need four spaces, three with direct street access and not tandem, is the strictest on this page.
Two rules that are not on the list but stop more projects
Trees. Not a zoning rule, but a by-law in its own right, and in Toronto the one that fails more lots than setbacks do. "Starting September 1, 2026, changes to Toronto's Tree Bylaws come into effect," with stronger protections for existing trees (Toronto tree and ravine protection permits). A protected tree's root zone can make a setback-compliant position unbuildable.
Servicing. Whether water and sewer come from the house or need a separate municipal connection. Richmond Hill requires the lot to be separately serviced (Richmond Hill ARU page); Vaughan and Milton require municipal services at all; Burlington bars private well, cistern and septic (09-2026 handout, above). Not a dimension, but a yes-or-no that comes before any of them.
The cities, side by side
Every figure in this table has a live official source. "Zone" means the city does not publish a single figure and it comes from your zone.
| City | Separation from house | Max height | Rear / side setback | Floor-area or coverage cap | Path width · max length |
|---|---|---|---|---|---|
| Toronto (garden) | 4.0 m if ≤4.0 m tall; 7.5 m if taller | 4.0 m within 7.5 m of house; 6.3 m beyond; 2 storeys | 1.5 m rear (greater of 1.5 m or ½ height on lots >45 m deep); side per frontage formula | 120 m²; 60 m² one storey; < house | 1.0 m (0.9 sprinklered) × 2.1 m · 45 m (90 m with measures) |
| Toronto (laneway) | 4.0 m / 7.5 m (By-law 847-2025) | 4.0 m / 6.3 m at 7.5 m separation | per Ch. 150.8 | < house GFA; all ancillary buildings ≤30% of lot | 0.9 × 2.1 m · 45 m (90 m through the lane with measures) |
| Etobicoke | as Toronto garden | as Toronto | as Toronto | as Toronto | as Toronto |
| Brampton | 3.0 m | lesser of house or 4.5 m (7.5 m Hamlet/Estate/Ag) | 2.5 m rear; 1.8 m side | 35 m² (80 m² Hamlet/Estate/Ag) | 1.2 m · not stated |
| Oakville | 2.0 m threshold: below it, main-building yards apply | 4.0 m from grade | 1.2 m interior side and rear; 3.5 m flankage (By-law 2026-088) | greater of 5% of lot or 42 m² | not published |
| Burlington | 4 m | 7 m peaked / 6 m flat | 1.2 m → 3 m above 4.6 m peaked / 3.5 m flat | 80 m² (15% of lot in LN5/LN6); 45% lot coverage | 1.2 m · not stated |
| Hamilton | zone | zone | zone | zone | not published |
| Vaughan | 4.0 m | zone | zone | ≤ house GFA; 45% coverage or zone max | 1.2 m walkway · not stated |
| Markham (permanent detached ARU = accessory building) | 4.0 m if ≥15 m² | 4.0 m (lots ≤4,000 m²); 5.5 m larger | 1.2 m; 0.5 m blank wall | 15 m² (lots ≤500 m²); 60 m² larger; lane-accessed lots: greater of 15% or 40 m² | 1.2 m (temporary garden suite rule only) |
| Richmond Hill | 4.0 m main wall to main wall | 2 storeys; 6.0 m main wall; 7.5 m overall | 1.2 m rear; 1.2 m side | 80 m² building coverage; excluded from lot coverage | 1.0 × 2.1 m · 45 m |
| Caledon (R1 group) | 3 m min; nearest wall ≤10–15 m (RE/RR/A) | 4.5 m (R1 group); ≤ house (RE/RR/A) | 1.2 m rear and side (R1); 4.5 m rear / 3 m side (RE/RR/A) | 80 m² and ≤ house ground floor (R1); 110 m² (RE/RR/A); 45% coverage | 1.2 m (1.0 m along a wall) |
| Pickering | not published | not published | not published | not published | not published |
| Ajax | 3.0 m from any building | 4.5 m; 6.1 m above a garage | 0.6 m any lot line | < house ground floor; aggregate accessory ≤ least of 60 m², 10% lot, zone coverage; 45% lot coverage | 1.2 m |
| Whitby | not stated | 4.5 m (general accessory rule) | 0.6 m interior/rear (general accessory rule) | not published | not published |
| Oshawa | 3 m | 4.5 m (5 m R1-G/R1-H) | 0.6 m interior side and rear | coverage: most restrictive of 8% lot / 50% house / 60 m² ground floor | 0.81 m · not stated |
Reading the table honestly
Three things stand out, and none of them is a sales point.
The spread is enormous. A permanent detached unit on a standard Markham lot is capped at 15 m²; Brampton's cap is 35 m²; Oakville's coverage cap of 42 m² bites on any lot under 1,100 m²; Toronto allows 120 m². If you own in Markham, Brampton or Oakville, the size you can build is set before the design starts, and it is small.
Height is the second filter. A one-storey, low-slope suite clears every city on this page. A two-storey suite clears Toronto (beyond 7.5 m from the house), Richmond Hill, and Burlington (7 m peaked) — and that is roughly the list of cities that publish a figure allowing it.
The access path is the quiet one. Nobody plans a project around a 1.2-metre strip down the side of the house, and it is the measurement most likely to be missing. It also tends not to be a variance item: the city does not grant relief from fire access.
How we use these rules
We measure the lot before we draw the suite. That means the survey first, the by-law for the zone second, and a position on the lot that clears every row in the table for that city, including the path and the trees, before a floor plan is chosen. Where a pre-approved plan fits inside that envelope — Toronto, Mississauga, Richmond Hill, Caledon, Pickering and Whitby publish them — we use it. Where it does not, the suite is drawn to the envelope rather than the envelope argued toward the suite. See pre-approved garden suite plans.
The permit process that follows is in garden suite permits in Ontario. The cross-city tracker, maintained by-law by by-law, is garden suite rules across the GTA. For Toronto and Mississauga lots, the measurements above are the ones the feasibility check runs against your address.
Disclaimer: Figures cited are market estimates provided for information only and are not a quote. Municipal rules, fees, and programs change — always verify current requirements with your local authority. Modular X provides exact pricing only after a site-specific feasibility review.