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This paper contributes to the classical problem of extracting properties of afinite group $G$ from the ring isomorphism class of its integral group ring$\mathbb{Z} G$. This problem is considered via describing the unit group$\mathcal{U}( \mathbb{Z} G)$ generically for a finite group. Concretely weobtain a new generic construction of units in $SL_1(\mathbb{Z} G)$ which areproven to extend, for natural classes of groups, with infinite index thecurrent known constructions. Moreover this new construction also exhibits newproperties, such as providing generically free subgroups of large rank. As anapplication we answer positively for several classes of groups the strongestform of the recent conjectures on the rank and torsion of the abelianisation$\mathcal{U}(\mathbb{Z} G)^{ab}$. To obtain all this, we investigate the groupring $R \Gamma$ of an extension $\Gamma$ of some normal subgroup $N$ by a group$G$, over a domain $R$. More precisely, we obtain a direct sum decomposition interms of various twisted group rings of $G$ and concrete information on thekernel and cokernel of the associated projections. Along the way we also launchthe investigations of the unit group of twisted group rings and of$\mathcal{U}( R\Gamma)$ via twisted group rings.

Units of twisted group rings and their correlations to classical group rings