1.   If the crack appears only in winter, it could be as simple as drying caused by reduced indoor humidity.

2.   Remember that reducing indoor humidity is important if condensation is a problem.

3.   The colder it is outside, the drier the air is inside because more heat is used, and heat lowers the indoor humidity level.

4.   This central humidifier is controlled by a room-mounted humidistat to monitor the outdoor temperature and automatically adjust the indoor humidity level.

5.   --Control indoor humidity, because dust mites particularly, but also cockroaches, thrive in humid conditions.