How do I prevent condensation in my four-season sunroom during Ottawa winters?

Condensation is a common problem in four-season sunrooms, and it gets worse as the weather gets colder. When the room is kept comfortably warm and the outdoor air is far below freezing, the inside surface of the glass gets cold. Moisture in the indoor air condenses on the coldest surfaces. Left alone, chronic condensation can lead to mould, rot and damaged finishes.

The most effective defence is glass that keeps its inside surface warm. High-performance insulated glass, typically triple-pane with low-E coatings and gas fill, stays much warmer on the room side than older double-pane or single-pane glass. Because condensation forms when a surface drops below the dew point of the indoor air, warmer glass means far less condensation. Warm-edge spacers help keep the edge of the glass, where condensation usually starts, from getting as cold.

Frames matter as much as the glass. Metal frames without a thermal break conduct cold to the inside and often show condensation or frost first. Ask for vinyl, fibreglass or thermally broken aluminum frames, and compare the rated performance of the complete window, not just the glass.

Indoor humidity is the other half of the equation. Cooking, showers, plants and people all add moisture, and a humidifier on your furnace can add more. A simple hygrometer lets you see how humid the house is. If you see condensation on cold mornings, lower the humidifier setting during the coldest weather and make sure bathroom and kitchen exhaust fans actually vent outside and are being used.

Air movement helps too. Still air sitting against cold glass condenses more readily than moving air. A ceiling fan on low can keep warm air circulating past the windows. If the room is heated with a ductless heat pump, place the indoor unit so its airflow sweeps across the glass wall. Heat from a warm floor rises along the glass, which is one reason in-floor heating suits glass rooms. Heavy blinds or curtains that trap cold air against the glass can make condensation worse, so leave a gap or open them during the day.

During construction, the hidden condensation inside walls and roofs matters even more than what you see on windows, because it can cause rot and mould that goes unnoticed for years. Ask your contractor how the air barrier and vapour control layer will be made continuous, especially at the connection to the house, and how the roof is detailed. The City's inspections review the work at set stages.

When comparing quotes from sunroom contractors in the Ottawa Construction Network directory, ask each to explain their glass specification and air-sealing details.

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

• Homeupgraders
• RenoMotion Inc.
• Elie The Carpet Guy Inc.
• The Fixer
• Transitions Renovations