How much does a home addition cost in London, Ontario?

A home addition in London, ON typically costs $150–$300 per square foot, depending on complexity. A 400 sq ft main-floor addition runs $60,000–$120,000. A second-storey addition over an existing footprint typically costs $180,000–$350,000 for a full floor.

Home Addition Cost in London, Ontario (2026 Complete Guide)

With Ontario home prices remaining high, many homeowners in London, Woodstock, Stratford, St. Thomas, and surrounding communities are choosing to expand their existing homes rather than move. A well-planned home addition adds the space you need while significantly increasing your property value. Here's what it costs in 2026 and what to expect.

Home Addition Cost Overview for London & Southwest Ontario

Addition Type	Cost Range	Notes
Main-Floor Room Addition (400 sq ft)	$60,000 – $120,000	New bedroom, family room, or home office
Garage Conversion to Living Space	$35,000 – $65,000	Insulation, HVAC, flooring, drywall
Sunroom / 3-Season Room	$25,000 – $55,000	Glass walls, basic HVAC, foundation
Full Second-Storey Addition	$180,000 – $350,000+	2–4 new bedrooms, bathrooms, structural work
Rear / Side Addition (600 sq ft)	$90,000 – $170,000	Extends main floor footprint, requires foundation

What Drives the Cost of a Home Addition in Ontario?

1. Foundation Work

Any addition that expands your home's footprint requires a new foundation. This is one of the most significant costs — typically $15,000–$40,000 depending on size, soil conditions, and whether a full basement under the addition is desired. Homes in London, Woodstock, and most Southwest Ontario communities are built on clay soil, which can add complexity.

2. Structural Engineering

A second-storey addition requires engineering drawings and may require reinforcing the existing structure. Structural engineering fees typically run $3,000–$8,000. This cost is non-negotiable — any reputable contractor in Ontario will require stamped engineering drawings before starting a second-storey addition.

3. Roofline Integration

Blending the new addition's roofline with the existing home is both an architectural challenge and a significant cost driver. A simple shed roof is most affordable. Matching an existing peaked or hip roof adds cost but looks far better and protects resale value.

4. HVAC Extension

Extending heating, cooling, and ventilation into the new space typically costs $4,000–$12,000 depending on whether your existing system can handle the added load or needs to be upgraded.

Most Popular Home Additions in Southwest Ontario

Main-Floor Master Suite Addition

Adding a main-floor primary bedroom with an en-suite bathroom is the most popular home addition in London, Woodstock, and surrounding communities — especially for aging-in-place planning. A 400 sq ft addition with bedroom + en-suite typically costs $80,000–$130,000.

Second-Storey Addition

For families who need more space but have a small lot, building up is the answer. A full second-storey addition adds 2–4 bedrooms and 1–2 bathrooms. This is the most complex and expensive type of addition, but it can double your home's living space without sacrificing yard area. Most common in London's older neighbourhoods where lots are too small to build out.

Rear Family Room Addition

Extending the back of the home to add a larger kitchen-dining-family room open concept is extremely popular in Hamilton, Brantford, Guelph, and London. This type of addition typically costs $90,000–$170,000 for 500–700 sq ft.

Home Addition Costs by City Near London, ON

London, ON: $150–$280/sq ft for main-floor additions
Woodstock: $140–$260/sq ft
Stratford: $145–$265/sq ft
St. Thomas: $135–$255/sq ft
Guelph: $160–$300/sq ft
Hamilton: $155–$290/sq ft
Kitchener / Waterloo: $160–$295/sq ft

Does a Home Addition Increase Property Value?

Yes — a well-executed home addition in Southwest Ontario typically returns 50–80% of its cost in added home value immediately, with the remainder captured at resale. A second-storey addition that takes a 3-bedroom bungalow to a 5-bedroom two-storey home can add $200,000–$400,000 in market value in London's current real estate market, often significantly exceeding the construction cost.

How Long Does a Home Addition Take?

Permit approval: 4–12 weeks depending on city and complexity
Main-floor room addition: 3–5 months total
Rear or side addition: 4–6 months total
Full second-storey addition: 6–10 months total

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Frequently Asked Questions

A home addition in London, ON typically costs $150–$280 per square foot. A 400 sq ft main-floor addition runs $60,000–$120,000. A full second-storey addition typically costs $180,000–$350,000 depending on scope and finishes.

A main-floor room addition takes 3–5 months including permits. A full second-storey addition typically takes 6–10 months from permit application to completion.

Yes, all home additions in Ontario require a building permit. Expert Renovation handles the full permit process — design drawings, submission, and city coordination — on your behalf.

In most cases, adding on is significantly cheaper than moving when you factor in land transfer tax, realtor fees, moving costs, and the premium you'd pay for a larger home in Ontario's market. A $150,000 addition typically costs far less than the $300,000–$500,000 price gap between your current home and a larger one.