In this paper, the HZ-length of different groups is studied. By definition, this is the length of HZ-localization tower or the length of transfinite lower central series of HZ-localization. It is proved that, for a free noncyclic group, its HZ-length is ≥ ω + 2. For a large class of Z[C]-modules M, where C is an infinite cyclic group, it is proved that the HZ-length of the semi-direct product M ⋊ C is ≤ ω + 1 and its HZ-localization can be described as a central extension of its pro-nilpotent completion. In particular, this class covers modules M , such that M ⋊ C is finitely presented and H 2 (M ⋊ C) is finite.