Drywall cracks because they are overloaded or because the structure has settled or heaved. Vertical and angled cracks are usually caused by settlement or heaving. Horizontal cracks are more likely to be caused by lateral pressure.
Settling is usually not uniform, certain parts of the structure will settle before others. A crack caused by a settling problem is generally located in the line between the ceiling and the wall, because of downward movement. Another common place for settlement cracks is along the top edge of a door frame. These cracks are usually diagonal and will continue the grow as the house settles.
Moisture can also form behind the drywall. If there was no vapor barrier placed behind the wall, moisture can be pulled in from outside, pass through the wall board and settle near the studs. Another problem is moisture reaching drywall screws. This causes the screw to rust and expanding rust will eventually cause drywall to crack.
Methods of Repair
The nature of the crack will determine the best mode of foundation repair or waterproofing that is needed to solve the problem. Possible solutions include underpinning, crack injection, wall plate anchors, helical tiebacks, drainage and gutter or downspout repairs. Often times water is often blamed for a structural issue – i.e. after a foundation has settled cracks will open and water will find a way into the living space. The lack of water can often be the cause of structural issues that do not get noticed until the wet season arrives and water starts infiltrating the foundation.
Water often causes foundation problems also and repairing the foundation without solving the real problem – water, can lead to future problems. This is often the case with standing water in the yard due to poor drainage. Hydrostatic pressure can build behind an otherwise stable wall and cause movement of this wall.