We have clay shale underneath our house, and the company that built homes in this area ignored that important issue. These homes in this area were built in 1955 without the proper foundation, so we always get cracks on our walls as the ground shrinks and stretches with the rain.
Some years ago, I had a contractor put metal plates between the floor's rafters and the foundation. It helped about 80%, and the cracks are now limited to our living room, and nothing on the exterior. I recently did the patch work in our living room, because we have family and friends coming to our home for the all day New Year's meal. My brother in law who lives in San Francisco said he's bringing the crabs and sashimi, and my sister in law brings the teriyaki chicken.