The anchoring is just as important as the rest of the structure of the safe room. Concrete pads are usually 4-inches thick, and they have plenty of mass and weight to secure the unit. Torshel only uses HILTI expansion bolts, and Epoxy Anchors (3/4- inch diameter by 4, ¾- inch length) -one every 12”. Once installed, each bolt withstands 10,000 pounds of pullout pressure. Depending on the size of the shelter, the installation will require between 13 to 50 bolts.