Tony from Montreal has problems with cracks in his walls.
All of the cracks followed drywall joints just above the corners of windows and doors.
Tony thought it was his electrical radiant heating in the ceiling that was causing the problem. This could be partially true, but more likely it is related to poor dyrwall placement and radical swings in humidity from summer to winter.
Drywall joints should never follow the corners of windows or doors
The corners of these wall penetrations are the places in the wall with the most stress. Drywall joints right at these stress points will amost always crack.
Window or doors should be cut out of the piece of drywall, or joints should be located over and under windows and over doors, but never in the corners. Hence dyrwall should be notched out for the corners, even if if this is going to waste some drywall. Follow this link for a video on techniques on cutting drywall, plus how to cut the notch for windows and doors, called "Chairing the board" (making a chair form out of it).
Humity swings can increase the stress
In the winter, the house tends to dry out partially because of the heating, but mostly because of cold air blowing through household cracks, picking up moisture and blowing out the other side. One of the quickest ways to raise the wintertime humidity in a house is to "air seal" -- weather-stripping and caulking. (This will also save a lot on the heating bill.) With humidity swings evened out, the cracks should minimize and can then be properly patched with drywall tape and drywall compound that might now be able to withstand further wall movement.
When drywall fails at the joints between pieces it often causes the delamination of the joint tape, not any real damage to the drywall itself. Follow this link for a video on repairing drywall delamination.