Bill 23 changed coach houses in Ottawa. What used to be a planning-committee fight is now a permitted use across nearly all residential zones, provided the lot meets the rules. The result is a steady stream of homeowners in Glebe, Westboro, Hintonburg, Manotick, and Sandy Hill calling about a coach house in the back yard.
The question is no longer "can I" but "what shape." Here are the five coach house layouts I have built repeatedly in Ottawa, with real square footage, the cost drivers behind each, and which lot conditions each one fits. The right layout depends on lot width, lot depth, the existing primary house, and whether vehicle access already runs to the rear.
1. The 600 sq ft compact one-bedroom (single storey)
Best ford7ae87f">Best ford7ae87f">Best ford7ae87f">Best ford7ae87f">Best for: lots 30 to 40 feet wide, with at least 20 feet of rear yard depth available. Cost drivers6ac">Cost drivers6ac">Cost drivers6ac">Cost drivers6ac">Cost drivers: slab-on-grade foundation, simple gable roof, one full kitchen and bath, services run from the primary house. The smallest footprint we build, and the most reachable total for most homeowners.
The compact single-storey is the smallest practical coach house. 20 by 30 feet outside dimensions, one bedroom, one full bathroom, an open kitchen-living-dining great room, and a small entry vestibule. The roof is a simple gable, the foundation is a slab on insulated grade, and there is no second floor.
This layout fits older infill lots in Centretown and Hintonburg where the rear yard is shallow. It works because it stays below the 6.4 metre height limit for accessory dwellings, sits within typical 1.2 metre side yard setbacks, and does not require a parking variance.
This is the lowest-cost coach house we build. It is not the cheapest per square foot (the smaller footprint means the kitchen and bathroom drive a higher per-foot cost), but the total dollar number is reachable for most homeowners.
2. The 900 sq ft over-garage two-bedroom
Best for: lots with existing rear-yard parking pad or driveway running through to the back. Cost drivers: the clear-span structure over the garage doors, two-storey framing, full unit fit-out upstairs.
The classic carriage house. Two-car garage on the ground floor, a 900 to 1,100 sq ft two-bedroom unit upstairs with the kitchen and living room running along the back wall and the bedrooms along the front.
This is the layout that pays for itself fastest. The ground-floor garage replaces a vehicle storage need, the upstairs unit commands strong two-bedroom rent in Ottawa, and the structure occupies the same lot footprint as a freestanding garage.
The structural challenge is the 22-foot clear span over the garage doors. We use engineered floor joists (typically 14-inch TJI or open-web steel) and a flush-frame header above the doors. The structural engineering letter is required on this style and is itemized in the quote.
3. The 1,200 sq ft two-storey three-bedroom
Best for: larger Manotick, Kanata, and rural Ottawa lots over 60 feet wide. Cost drivers: full two-storey freestanding structure, two bathrooms, larger footprint, likely Minor Variance.
The full three-bedroom coach house works on the larger suburban lots that can absorb a second freestanding home. Two storeys, 30 by 20 footprint, three bedrooms upstairs, full living-kitchen-dining downstairs, half-bath on the main floor, full bath upstairs.
This is the layout for multi-generational families. Adult children moving back to Ottawa, aging parents who want independence on the same property, or owners who want the option to fully separate the rental at some future date.
The zoning catch is that on most R1 and R2 zones the maximum gross floor area for an accessory dwelling is capped at 80 square metres (about 860 square feet). A 1,200 square foot coach house often requires a Minor Variance application, which adds 4 to 8 weeks plus the City's application fees. We check this against By-law 2008-250 before issuing any quote.
4. The 700 sq ft accessibility-focused single-storey
Best for: aging-in-place planning, families with mobility needs. Cost drivers: accessibility features (wider doors, curbless shower, accessible kitchen), single-storey footprint, graded path of travel.
A single-storey coach house designed from day one with accessibility built in. 36-inch interior doors, a curbless walk-in shower, lever-style hardware throughout, an accessible-height kitchen with a roll-under sink option, and a path of travel from the primary house to the coach house door at no greater than 1:20 grade.
This layout is increasingly common with families who plan to move a parent into the coach house in 5 to 10 years. Building it accessible from the start costs about 8% more than the standard layout. Retrofitting accessibility later costs 35% more and rarely produces as clean a result.
For specific design and code points, see our accessibility renovation page. The OBC requirements for visitable units in accessory dwellings are also called out in our coach house service page.
5. The garden-suite duplex (two units in one coach house)
Best for: investor owners on larger lots, multi-generational families with two distinct households. Cost drivers: two separate services, two heating systems, fire-rated separation between units, more complex drawings and longer build.
Bill 23 in Ontario allows up to three residential units on most existing lots, including the primary house and accessory dwellings. A duplex coach house contains two separate units (typically one bachelor on the ground floor and one one-bedroom upstairs, or two side-by-side one-bedroom units on a wider lot).
The financial case is the strongest. Two rental units producing combined income against a single build, which on current mortgage rates covers debt service with margin to spare. It is the highest-revenue coach house layout we build.
The complications are real. Two separate electrical services from the meter base, two heating systems (or zoned), separate water shut-offs, fire-rated separation between units (1-hour fire wall and floor assembly), and OBC §9.10 fire code compliance throughout. The architectural drawings get more complex. The permit fee is higher (calculated on total floor area). The construction is longer.
Servicing the coach house: the buried cost most quotes miss
The coach house structure itself is one cost. Running services to it is another. Water, sewer, and electrical from the primary house or street to the coach house can add substantially to the project depending on distance, soil conditions, and whether the trench has to cross existing landscape or hardscape. We always quote services as a separate line item with the actual route surveyed before the number is set. The contractors who quote coach houses without a serviced-cost line are the contractors whose final invoices come in well over. The other big-ticket extra is heating: the most economical approach is a separate cold-climate heat pump (Mitsubishi or Daikin hyper-heat) per coach house unit, sized for the volume, which we itemize as its own installed line.
How long does it actually take?
- Lot feasibility review: 48 hours (free with us)
- Architectural drawings (BCIN-stamped): 8 to 14 weeks
- Structural engineering letter: 2 to 4 weeks (parallel)
- Permit submission via MyServiceOttawa: 1 day to submit, 8 to 16 weeks for review
- Construction start to finish: 6 to 11 months depending on layout
- Total from first call to occupancy: 12 to 18 months
The honourable-mention layouts
Two layouts I do not recommend but get asked about often:
- The studio-only coach house (under 400 sq ft): too small to comply with OBC minimum room dimensions for a separate dwelling, and produces a unit that rents for less than the construction cost can support.
- The detached studio attached to a deck or pergola: usually fails permit because it does not meet the structural separation requirements between the dwelling and the accessory structure.
The coach house that succeeds is the one that fits the lot, fits the by-law, and is built for what the homeowner actually plans to do with it. The coach house that fails is the one designed to maximize square footage at the expense of either constraint.
What separates a good coach house design from a bad one
The answer is the relationship between the primary house and the coach house. The successful projects treat the two buildings as a pair, with intentional sightlines, privacy screening, and architectural language that pulls them together. The unsuccessful ones treat the coach house as a standalone box dropped in the back yard, ignoring the fact that the primary house's master bedroom now looks straight into the coach house kitchen window.
Spend the design phase getting that pair right. The bedroom-to-bedroom sightline matters. The fence and landscaping matter. The path between the two buildings matters. Build a coach house that respects the existing house and the existing house gets better. Build one that ignores the existing house and you have just bought yourself a 30-year zoning headache.
For the full breakdown of how we plan, permit, and build coach houses in Ottawa, see our coach house builder Ottawa page.