How much does it cost to build an attached garage addition onto my Ottawa home?

Building an attached garage addition in Ottawa typically runs between $55,000 and $120,000 for a standard single-car garage, and $85,000 to $180,000 for a double-car addition. These figures reflect Ottawa's 2025-2026 construction market, including materials, labour, permits, and the foundation work needed for our climate.

The biggest cost driver is the foundation. Ottawa's frost line sits at roughly 48 inches (1.2 metres), and the Ontario Building Code requires your footings to extend below that depth. This means you're excavating significantly deeper than builders in milder climates, and the concrete volume adds up quickly. A full-depth foundation for a two-car attached garage can run $18,000 to $35,000 on its own, depending on soil conditions and whether you hit rock or high water table, both of which are common in neighbourhoods like Barrhaven and Kanata.

Structural tie-in to your existing house is another major line item. The new garage wall has to connect seamlessly to your home's framing, and the roofline needs to integrate properly so water doesn't pool at the junction. Flashing, weeping tile extensions, and waterproofing where the new foundation meets the old one typically add $5,000 to $12,000 depending on complexity. If your home has a brick or stone exterior, matching the masonry and tying the new garage into the existing facade pushes costs toward the higher end.

Other costs to budget for include the building permit from City of Ottawa Building Code Services, which runs $1,500 to $4,000 depending on the scope, plus electrical hookup for lighting, an opener, and at least one or two dedicated outlets. If you want a heated garage, adding a gas line and unit heater or in-floor radiant heat will add $3,000 to $8,000. Most homeowners also invest in proper insulation even for an unheated garage, since the shared wall with your house needs to meet code requirements for thermal separation anyway.

Get at least three detailed quotes from contractors who have experience with attached additions specifically, because the structural integration is more complex than a detached build. Ask to see their WSIB clearance certificate and make sure they pull the permit through the City rather than asking you to do it yourself, which can be a red flag.

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