Greenhouse foundation - Deeper dive into how to use the j-bolts to secure your foundation: 1 - Close up of a J-bolt and the bolt & washer. 2 - Setting the J-bolt in the concrete block showing about how much of the threads should be above the sill plate so it can be bolted down. 3 - J-bolt ready to have concrete added to the hole. After adding the concrete make sure the hook is fairly straight (vertical) before the concrete sets. 4 - The sill plate is bolted down.