What is the best roof style for an addition on a century home in Ottawa?

Adding onto a century home calls for careful attention to the roofline, because the wrong roof style can make even a well-built addition look like an afterthought. Many of Ottawa's older homes have steep gable roofs, hip roofs or other forms typical of their era. Your addition's roof needs to respect that character while meeting the Ontario Building Code (OBC) for structural loads and energy performance.

For many century homes, a gable roof is the most natural choice. It matches the dominant roofline of many Victorian, Edwardian and early 20th-century houses. Ideally, the pitch should closely match the existing roof. A steep pitch also sheds snow well, which reduces the ice dam risk that lower-slope roofs face in a cold climate with frequent freeze-thaw cycles.

If your house has a hip roof, a matching hip or cross-hip on the addition keeps the look consistent. Hip roofs are strong and sit well in the wind, but they involve more framing and more complicated roofing, so they usually cost more than a simple gable. Ask contractors to price both if you're unsure.

A shed roof can work well for smaller single-storey additions, such as a sunroom or a kitchen bump-out, especially when the addition sits below the main roofline. It is common on older homes where a full gable would overwhelm the house or block upper-floor windows, and it is usually the simplest roof to frame. The main watch-outs are the low pitch, which needs roofing suited to low slopes, and the junction with the house wall.

Heritage rules may apply. If your property is designated or sits in a Heritage Conservation District, the City must approve alterations including the construction of an addition, and your roof design will be part of that review. Check your property's status with the City before you finalize the design.

The connection between the existing roof and the addition is where most problems happen. A poorly detailed valley or wall junction can leak within a few winters. Ask your contractor how they will run self-adhered ice and water membrane in the valleys and along the junction, and how step flashing and counter-flashing will be installed where the addition meets the existing wall. On older houses, the existing roof framing may also be undersized or uneven by modern standards, so expect the contractor to open it up and assess it.

Whatever the style, the roof structure must be designed for snow loads under the OBC, including drifting where a lower addition roof sits beside the taller house. Your designer or a professional engineer will size the rafters or trusses. You can browse addition contractors in the Ottawa Construction Network directory, ask to see older-home additions they have completed, and compare itemized quotes.

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

• 613Bins
• RenoMotion Inc.
• Prism Services
• Dreamwood Construction & Renovations
• Somar Contracting Inc.