Dean: Thank you for contacting Porch. A sinking structure could be caused by soil and or drainage issues. Since you asked this question under plumbing services possibly you know there is a pipe leak causing erosion and resultant movement of the garage. Best action is to get a plumber out to evaluate and determine the source of the leak and repair, then a foundation repair contractor can evaluate and determine the method to correct the sinking structure. You can locate a local pro at this webpage https://pro.porch.com/near-me/plumbers or call us at 1-855-707-0141 to get started. For a foundation repair contractor you can go to this webpage and input your zip code: https://pro.porch.com/near-me/foundation-repair.