The adatom site is identified and determined as the main structural element of Sb-induced surface reconstructions of Si͑113͒ by means of x-ray standing waves, x-ray photoelectron spectroscopy, and low-energy electron diffraction ͑LEED͒ in combination with density functional theory calculations. The analysis yields that the Sb adatom site can be found prevalently at Sb coverages below 1 ML. With increasing coverage, the relative amount of Sb residing in adatom sites is reduced in favor of mainly Sb tetramer formation, leading to a complex mixture of ͑2 ϫ 2͒ reconstructions at coverages above 1 ML. The observation of ͑1 ϫ 2͒ LEED patterns can be explained by the formation of small antiphase domains of ͑2 ϫ 2͒ reconstructions. Upon annealing, partial desorption of Sb leads to the formation of a missing-row structure with a ͑1 ϫ n͒ LEED pattern.