What is the cost of a full second-storey addition versus a partial one in Ottawa?

If you are building up rather than out, you face a basic choice: a full second storey over the entire footprint of the house, or a partial second storey over only part of it. The cost difference depends on structure, roofline complexity and how much interior finishing is involved.

As broad perspective, a full second storey over a typical bungalow footprint can range from roughly $250,000 to $450,000 depending on size, structural work and finishes, and a partial second storey usually costs less in total. Treat those as perspective, not a quote.

Cost per square foot can be higher on a partial addition. You still pay for structural engineering, roof tie-ins and mechanical connections whatever the size, and those fixed costs are spread over less floor area. The junction between the new upper level and the remaining old roof also adds flashing, insulation and weatherproofing details that a full second storey avoids.

Structural engineering is critical for both. The existing foundation and walls must carry the new load. A structural engineer will check whether footings and walls need reinforcement, and that finding can change the budget more than anything else. If the house sits on sensitive clay such as Leda clay, footing sizes must be engineered. A full second storey can spread the load more evenly than a partial one, which sometimes simplifies the structural solution.

Permits and energy rules. A second-storey addition needs a building permit. Under the 2026 schedule the fee is $12.75 per $1,000 of construction value (minimum $117), so a $300,000 valuation would be about $3,825, though the City confirms the valuation. The addition must also meet SB-12 for additions, through a compliance package or the addition table, which includes an attic ceiling at R-60 and above-grade walls at R-19 plus R-5 continuous insulation. Check your zoning's height limit before design work starts. Contact Building Code Services if you have questions.

Temporary living arrangements. A full second storey usually means removing the existing roof, so many families move out during framing and weather-tightening. Ask your contractor how long the house will be open and put that cost in your budget. A partial addition may let you stay, though it will be disruptive.

Timing matters. Winters regularly reach well below -20°C, so many contractors prefer to open roofs between late spring and early fall. Starting a full roof removal late in the year usually means paying for more weather protection.

To compare itemized quotes for both approaches, you can browse addition contractors in the Ottawa Construction Network directory.

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Looking for experienced contractors? The Ottawa Construction Network connects homeowners with qualified professionals:

• Luxe Painting and Renovations
• JC Carpentry
• JMY Renovations
• Vanguard Environmental
• Speedy Pete's Inc