When diagnosing if a home has foundation settlement problems, exterior cracks are one of the most visible signs you will notice.
When foundation settlement has occurred, stair-step cracks are commonly seen in brick and concrete block. In addition, long horizontal cracks may also be seen on brick home and horizontal cracking widens with increasing settlement.
As the problem gets worse, you may also begin to notice vertical cracking. Vertical cracking gets wider at the top than at the bottom due to wall rotation. when settlement occurs it is because the footing broke due to a void or insufficient support underneath. When the footing cracks, it settles and the home begins to lean in one direction. The crack that starts at the footing will gradually inch its way up the foundation wall as the footing sinks and the home leans. This is often why settlement cracks are very narrow down at the footing and become wider up higher.
Furthermore, because doors and windows are the weakest point in a wall, cracks extending from doors and windows are also very common.
Whether you see a crack that is horizontal, vertical, cracks in your brick that look like stair steps, theses visible signs should not be ignored. The problem can get worse over time and over time it will be more costly to get the repairs done.
Excerpt from: "Foundation Settlement, Chapter 1: Diagnosing Foundation Settlement", Foundation Supportworks, Got Tech. July 2014