Secondary Glazing and Ventilation

The two kinds of ventilation a room needs

Background ventilation is the small continuous airflow that carries moisture and stale air away, usually through trickle vents or the natural leakage of an old window. Purge ventilation is the fast air change you get by opening a window wide. Secondary glazing can remove both if it is specified carelessly, so the survey records what each room currently relies on before anything is ordered.

• Background: trickle vents and leakage
• Purge: opening the window wide
• Both are recorded at survey
• Extract fans handle kitchens and bathrooms

Trickle vents in a secondary unit

Where the primary window carries trickle vents, we fit matching vents in the head of the secondary frame so the path is continuous. Where the primary has no vents and the room relied on draughts, we discuss whether to add vents, since removing the leakage that was doing the job will change how the room behaves. Vents can be closable, so noise sensitive rooms can shut them at night and open them by day.

Escape windows and openable units

Any window designated as a means of escape keeps an openable secondary unit with a handle that releases from inside without a key. Fixed panels are never fitted over an escape window. Hinged casements are the usual choice there, because they clear the whole opening in one movement rather than needing a panel to be lifted out and put somewhere.

Rooms that need extra care

Bathrooms, kitchens, utility rooms and any bedroom where washing is dried indoors produce far more moisture than the rest of the house. In those rooms, sealing the window without checking the extract fan is how a condensation problem gets moved to a wall or a wardrobe. Nurseries and bedrooms of anyone with respiratory conditions also warrant a deliberate ventilation plan rather than a default.