What does it cost to extend a roofline for a second-storey addition in Ottawa?

Rebuilding or extending the roofline is one of the most structurally significant parts of a second-storey addition. Whether you are raising the whole roof, extending part of it over a partial addition, or tying a new upper roof into the existing one, the approach you choose affects cost, schedule and how the house looks when it is done.

Full roof removal and rebuild. Adding a complete second storey usually means taking off the existing roof and building a new one on top of the new walls. That includes demolition, new engineered trusses or rafters, sheathing, underlayment, the roofing itself, fascia, soffit and flashing. As broad perspective, the roofing part of a full second storey can range from roughly $40,000 to $80,000 depending on roof area, pitch and material. Treat that as perspective, not a quote.

Partial extensions. When the second storey covers only part of the house, the new upper roof meets the old lower roof. Those junctions create valleys, step flashing and waterproofing details that take careful work, so the cost per square foot is usually higher even though the total is lower.

Structural engineering. A structural engineer designs the new roof and checks the load path down through the existing house, including snow and wind loads for this location. The engineer's drawings are part of your building permit application. Ask whether engineering is in the contractor's quote or billed separately.

Material choice. Architectural asphalt shingles are the common choice and usually cost the least up front. Standing-seam metal costs more to install but is chosen by many people for its long life. Ask for both options priced on the same roof area, and get the product and workmanship warranty terms in writing.

Insulation. The new roof is part of the addition's energy compliance under SB-12. The verified addition table value for a ceiling with an attic is R-60. A ventilated attic with blown insulation reaches that fairly easily. Cathedral ceilings, often wanted in an upper-floor bedroom, need deeper rafters, exterior rigid insulation or spray foam to perform well. Your designer will confirm the assembly that meets the drawings.

Timing. Opening the existing roof needs a weather window long enough to frame and dry in the new structure quickly. Many builders plan this phase for the warmer months. Winter roof openings are possible, but they need temporary weather protection and heating, which adds cost. Ask each contractor how long the house will be open and what their weather plan is.

The permit fee for the addition is $12.75 per $1,000 of construction value (minimum $117) under the 2026 schedule. To compare itemized quotes, browse roofing contractors and addition builders in the Ottawa Construction Network directory.

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

• Justyn Rook Contracting
• RenoMotion Inc.
• Diamond renovations
• Elie The Carpet Guy Inc.
• Demontigny Carpentry