Trickle vents and ventilation when replacing windows

Tall grey tilt and turn window tilted open in a city apartment

In England, if your old windows had trickle vents, the new ones must have vents at least as large. If they did not, the room must be no less ventilated than before, which usually means fitting vents of about 8,000 mm² in each habitable room and kitchen and 4,000 mm² in bathrooms.

Why ventilation matters more with triple glazing

New windows are much more airtight than old ones. Background ventilation lets moisture and stale air out, which prevents condensation and mould on walls and in corners.

The rules in England

Approved Document F says a replacement window must not make ventilation worse. LABC guidance confirms that a disclaimer, or relying on a night-latch position, is not an acceptable substitute for vents.

What vents look like

A trickle vent is a slim slot with a closable cover, usually in the head of the frame. Acoustic vents are available for noisy roads.

Other ventilation

Extractor fans in kitchens and bathrooms, and mechanical ventilation systems in some homes, also count. We note what you have on survey and size the vents to suit.

Questions

Do I have to have trickle vents?

If your old windows had them, yes. If not, ventilation must be no worse than before, which usually means fitting them.

Do trickle vents let noise in?

Standard ones can. Acoustic trickle vents reduce that.

Sources

LABC: replacement windows and trickle vents

More guides

Get a free survey and quote

Free survey · written quote, no obligation