Windows covered in condensation

[UKBloke]

Thanks, that makes more sense.

 

[crank39]

It happens overnight because 2 people between them can expel upto 1 pint of water, this moisture will float around till it finds a cold surface to condensate on. You need to ventilate with either trickle vents OR put the window on night vent, but its cold and it defeats the object of double glazing, well welcome to my world, as a service engineer I have this conversation daily with our customers

 

[foxhole]

Why does this happen in unoccupied rooms?

It’s all on same floor air is circulating .

 

[UKBloke]

This is a bedroom window this morning, one person sleeping in here.
It’s odd that it’s worse at one end.

 

[pcaouolte]

This is a bedroom window this morning, one person sleeping in here.
It’s odd that it’s worse at one end.

Which end of the window is nearest to the sleeping person's head? Water vapour tends to condense on the first cold surface that it reaches.

 

[ronniecabers]

The condensation is due to excess water vapour , as mentioned created by simply breathing, cooking , bathing etc... A warm room will hold more moisture in the air so rooms with no heating will attract condensation. Doors closed on bedrooms will not allow moisture created from breathing when sleeping to dissipate.
As goes your existing windows, as mentioned the age of them suggestd they are just simple clear glass , rather than any of the energy saving types available today ( typically diamant/ warm edge spacer +argon gas / planitherm ( low e glass ). Your older sealed units will be getting colder than modern units due to cold transference ( warm edge spacer stops this) from the outside pane and no heat retention from the inner pane ( heat retention is what the argon gas and low e glass do ). Now if you fit modern units you should get less condensation on your sealed units BUT bear in mind your excess water vapour has not disappeared its still there and just finding another cold spot to condensate on. Trickle Vents may help but again they are not the ultimate solution, purge ventilation ( opening windows ) is by far the best way to dispell excess moisture but that's far from ideal in winter .
suggest leaving your bedroom door ajar overnight to move some of the moisture you are expelling when sleeping out of the bedrooms , it will only move it around the house , so the following morning I suggest opening the windows for an hour or so if the weather allows.
Don't get me wrong trickle vents will help but they won't solve the issue entirely. I have trickle vents and modern sealed units , along with Georgian bars ( as per ops picture) ... I sleep with my door closed (as I have annoying cats ! ) ... I still get condensation on my windows , albeit much less than I used to but I open my windows every morning to allow that excess moisture to leave the property

 

[^woody^]

Vents won't help.

You have old units and the cause is the thermal bridge from the aluminium spacers.

You may be producing high humidity elsewhere, so check your use of extract fans or moisture production, but this is a common issue with older frames and units.