Types of Home Additions and Their Costs
1. Single-storey bump-out addition
An addition that extends the existing footprint of your home on one side. Most common for kitchens, main-floor family rooms, or primary bedrooms.
| Size | Typical Cost Range |
|---|---|
| Small bump-out (under 200 sq ft) | $50,000–$100,000 |
| Standard room addition (200–400 sq ft) | $80,000–$160,000 |
| Larger addition (400–800 sq ft) | $160,000–$320,000 |
2. Second storey addition
Adding a full upper floor above an existing single-storey home. Structurally demanding — often requires reinforcing the existing foundation and first-floor walls.
| Size | Typical Cost Range |
|---|---|
| Full second storey (1,000–1,500 sq ft) | $250,000–$500,000+ |
| Partial second storey (bedroom + bath) | $120,000–$250,000 |
Second-storey additions require the occupants to vacate the home during the most disruptive phases, adding temporary housing costs.
3. Garage conversion to living space
Converting an attached garage into a bedroom, office, or family room. Lower cost because the structure already exists — no new foundation required.
| Scope | Typical Cost |
|---|---|
| Basic garage conversion (no bathroom) | $25,000–$60,000 |
| Full living space with bathroom | $50,000–$100,000 |
Note: Garage conversions require zoning approval and must meet building code for habitable space (ceiling height, insulation, egress windows, etc.).
4. Basement apartment / in-law suite
Finishing an unfinished basement and converting it to a legal secondary dwelling unit (SDU). Legality rules vary by municipality.
| Scope | Typical Cost |
|---|---|
| Basic legal suite (1 bedroom) | $60,000–$100,000 |
| Full 2-bedroom legal suite | $80,000–$150,000 |
See our cost of a basement renovation guide for more detail.
5. Sunroom / three-season addition
A sunroom (often unheated or minimally heated) adds square footage and light without the full cost of conditioned space.
| Type | Typical Cost |
|---|---|
| Prefab sunroom kit (installed) | $15,000–$35,000 |
| Custom sunroom (conditioned space) | $35,000–$70,000 |
Full Cost Breakdown for a Standard Addition
For a mid-range 400 sq ft single-storey addition:
| Component | Cost | % of Total |
|---|---|---|
| Design and engineering (architect, structural) | $8,000–$15,000 | 8–10% |
| Permits and fees | $2,000–$6,000 | 2–4% |
| Excavation and foundation | $10,000–$25,000 | 10–15% |
| Framing (walls, roof structure) | $15,000–$30,000 | 15–20% |
| Windows and exterior doors | $6,000–$15,000 | 5–10% |
| Roofing and exterior finishing | $8,000–$18,000 | 8–12% |
| Insulation | $3,000–$7,000 | 3–5% |
| Drywall and taping | $4,000–$8,000 | 4–6% |
| Electrical | $5,000–$10,000 | 5–7% |
| HVAC extension | $3,000–$8,000 | 3–5% |
| Plumbing (if applicable) | $3,000–$10,000 | 3–7% |
| Interior finishing (flooring, trim, paint) | $8,000–$18,000 | 8–12% |
| General contractor overhead and profit | 15–20% of subtotal | 15–20% |
| Total | $80,000–$170,000 |
Cost per Square Foot by Province
| Province | Cost per Sq Ft (Standard Addition) |
|---|---|
| BC (Lower Mainland) | $350–$500+ |
| Ontario (GTA) | $300–$450 |
| Alberta | $250–$380 |
| Ontario (other cities) | $220–$350 |
| Quebec (Montreal) | $200–$320 |
| Saskatchewan/Manitoba | $200–$300 |
| Atlantic provinces | $180–$280 |
| Smaller cities / rural | −15–25% vs. urban estimate |
Factors That Drive Up the Cost
Complex roofline integration
Attaching a new roof to an existing home that has a complicated roofline (valleys, dormers, multiple pitches) adds significant carpentry cost. A simple shed roof or flat-roof addition is cheaper than matching a complex hip or gable roofline.
Heritage home or unusual construction
Homes built before 1960 may have non-standard framing dimensions, knob-and-tube wiring that needs updating, and masonry or plaster walls that complicate the integration. These add $15,000–$30,000 to most addition projects.
Plumbing in the addition
Adding a bathroom, kitchenette, or laundry adds significant plumbing cost, especially if the main drains and vents need extending.
Engineered beam requirements
Removing a load-bearing wall to open up the addition to the main house often requires LVL (laminated veneer lumber) beams or steel beams, plus engineering stamp. Add $3,000–$8,000.
Permits and Zoning
Before starting design work, confirm your municipality’s rules:
| Requirement | What to Check |
|---|---|
| Building permit | Required for all habitable additions |
| Setbacks | Minimum distance from property lines (typically 1.2–6m) |
| Lot coverage | Maximum % of lot that can be covered by buildings |
| Height restrictions | Particularly relevant for second-storey additions |
| Heritage restrictions | Some older neighbourhoods have design guidelines |
Permit fees are typically $5–$20 per $1,000 of construction value, or $2,000–$10,000 for a major addition.
Home Addition vs. Moving: Which Is Cheaper?
In high-cost markets like the GTA and Metro Vancouver, adding space is often cheaper than buying a larger home due to:
- Real estate commissions (typically 3–5% of sale price)
- Land transfer taxes (provincial + municipal in Toronto)
- Moving costs
- Price premium for larger homes
Rough comparison (Toronto example):
- Cost to add 500 sq ft: $175,000–$250,000
- Upgrade from 1,400 to 2,000 sq ft home: likely $300,000–$600,000 price difference + $40,000–$80,000 in transaction costs
In markets with smaller price gaps between home sizes, moving is often more economical.