Behavioural economics are, amongst other things, concerned with the influence of social norms on behaviour. There has been empirical research on spillover effects across norms, but the need for a suitable theoretical framework has sometimes been neglected. This has led to confusions about the extent norm spillovers can have and the structural limits they inherit. This work presents a model based on Granovetter's model of thresholds which helps identifying the dynamics of norm adherence and long-run equilibria. This model also allows to address the question of the influence norms may have on the adherence of other norms and the limits thereof.