So much humidity in home over the winter
You get condensation because the windows (and evidently part of the ceiling, unless that's just a roof leak) are the most poorly insulated part of the building, so they cool below the dewpoint of the interior air.

Bay windows are particularly bad as they are a fairly large expanse of window stuck out into the cold, and not infrequently the non-window parts of the bay are not well-detailed from an insulation point of view. They also have a lot of joints making potential cracks to leak cold air.

Active ventilation can help remove some of the interior moisture (from whatever sources), but since your investigation has shown poor insulation, solving poor insulation is probably a good idea as part of the overall fix.


If you happen to be using an unvented gas heater for your heat, that
alone will add a huge (generally unacceptably huge) amount of water
to the indoor air (and replacing it with a vented heater will help
immensely.) Indeed, most houses are quite dry through the winter with
normal heat, which is why I mention that, as I half-suspect it.
If you have a gas range and your range hood is either not running
when you operate the range, or one of those useless range hoods that
does not actually exhaust air (merely recirculating it through a
filter) that will add water to the air.
Bathrooms without fans, or with unused or ineffective fans also add
water to the air.
Improperly vented clothes dryers or hanging laundry to dry in the
house add water to the air...


For a quick, inexpensive approach on the windows, consider using "window shrink film kits" for the winter. They effectively make an interior "storm window" and both reduce air leaks and radiative heat loss. If done carefully they don't look bad.