[ipsento606]

> Maybe some of my difficultly understanding is being American

In the UK, in winter, ambient exterior air is both fairly cold (let's say 40F) and extremely humid, often around 80% relative humidity.

Houses are both poorly insulated and poorly ventilated. Heating is (relatively) very expensive.

Most housing units don't have clothes dryers, and it's common to dry clothing indoors on wire racks.

The net result is that you end up with extremely humid indoor air in the 55F-65F range, while the exterior walls and windows of the building never really heat up properly.

It's a recipe for condensation on the interior surfaces of those walls and windows.

You can fix this either by heating the building enough that the exterior walls actually heat up beyond the dew point (which few people can afford to do), or by keeping windows open in winter to provide some ventilation (which makes the already-poorly-heated building even less comfortable).