The required anchor bolt layout is shown in Figure 2, Drawing No. 11465-C. Tower height is increased, in 20 foot increments, by adding new sections to the base of the tower structure. Each additional section is stronger and heavier, with a larger spread between the tower legs. Foundation size also increases with tower height. The most common foundation consists of a single large, square concrete pad with three anchor groups, illustrated in Figure 3. The pad must be deep enough to extend below maximum frost depth. The actual size of every foundation depends on wind conditions at the turbine site, local frost depth and soil conditions at the tower site.