UPDATE 2: Foundation & Plumbing
The new garage/ADU will be supported by frost footings. The footings guard against settling and slippage that can damage the new structure. They also keep posts and beams from direct contact with the earth. Going below the frost line helps prevent soil movement due to frost called “frost heave”.
Clean fill is brought in for backfill and to prep for the new slab. Sand helps the new Garage concrete slab in a couple of ways. First, it creates a good drainage plane over our sub-soil/existing soil, and it also aids in creating a level surface for the new slab. We’re replacing the excavated soil because it contains roots and stones that would prevent it from compacting, which could create voids and sinkholes, leading to foundation erosion. The soil removed at excavation is taken away and repurposed or used in re-grading the yard as needed.