Ventilation in a glazed extension

Replacement windows normally need background ventilation, which in practice means trickle vents or an equivalent system. They look like a nuisance and they are there because Approved Document F requires air movement in a habitable room without the window being left open.

In an acoustic specification, the vent has to be an acoustic vent, or it undoes the performance of the glazing it sits in.

Purge ventilation is the quick blast that clears steam from a shower or smoke from a kitchen. It comes from an openable panel or an extract fan. On a folding door, one panel can be specified to open on its own for exactly this purpose.

Moisture finds the coldest surface in a room. In a glazed extension that is usually the perimeter of the glass or the head of the frame. Air movement, a small heat source and correct detailing reduce it far more reliably than a dehumidifier used after the event.

A mechanical ventilation system with heat recovery supplies fresh air and recovers heat from the exhaust air, which suits an airtight extension where opening the doors defeats the point. It needs ducting designed in early, so it is a decision for the drawings rather than for the electrician.