Controlling Condensation with Secondary Glazing

Why Condensation Forms

Condensation forms when warm, moisture-laden room air contacts a cold surface. Windows are the coldest surface in most rooms during winter. Single-glazed windows can reach temperatures close to the external temperature on cold days, creating ideal conditions for condensation.

How Secondary Glazing Prevents Condensation

Secondary glazing eliminates condensation by keeping the inner pane (the secondary pane facing the room) warm. Because the secondary pane is insulated from the cold external glass by the air cavity, its surface temperature stays well above the dew point of the room air. No cold surface, no condensation.

Cavity Ventilation

A small amount of moisture may occasionally enter the cavity between primary and secondary glazing. We manage this by incorporating a discrete ventilation path between the cavity and the room, allowing any moisture to disperse rather than condense in the cavity. This is standard practice in all our installations.

Particularly Effective For

• Victorian and Edwardian sash windows with single glazing
• North-facing windows with limited solar gain
• Bedrooms and kitchens with higher humidity
• Ground floor and basement properties
• Properties near water or in high-humidity areas

When Condensation Persists

If condensation persists after secondary glazing is installed, it is usually forming on the secondary pane itself — which may indicate the cavity ventilation needs adjustment, or that the internal humidity is extremely high and requires additional ventilation or dehumidification.