Condensation on windows...but with low humidity levels

firsttimemover

Hi, I know there are numerous threads on internal condensation, particularly as the temperatures plummet, however most seem to point to high humidity levels.

However, after having condensation on our windows in the winter for the last couple of years, we have been particularly careful so far this year, making sure that the bathroom door is always shut during and after a shower and that the extractor runs for longer and the window is open until all the steam has escaped from the bathroom, as well as ensuring the kitchen door is shut when cooking and extractor hood running/window open when cooking on the hob. I've started working from home this year too, so the heating is on longer and temperatures more consistent throughout the day (most days) which I also thought might help.

We've been keeping an eye on the humidity levels and upstairs seems to be around the 40-45% mark, lower downstairs, however we are still getting bad condensation on the windows the morning. Noticeably more in our bedroom (presumably our breath) but this morning we even had condensation (albeit quite small amounts) on the windows in the lounge where the hygrometer is showing only 33% humidity, which everything I read seems to indicate is very low humidity.

The windows are double glazed, condensation seems to increase if we leave the bedroom window open slightly (at least on the open windows, presumably because it is a cooler surface). Is it the windows that need replacing (they are fairly old and don't have trickle vents), or is there something else I'm missing? I can't stand having to wipe down the windows each morning and fighting black mould around the window seals, but ideally don't want to go to the expense of replacing all the windows for the same thing to happen!

Any help/advice would be appreciated.