Current seismic codes assume a triangular distribution of base shear for isolated buildings similar to their fixed-base counterparts. In this paper the validity of such distribution is investigated for isolated structures having electrometric isolators. So different models of isolation systems are selected that cover a wide range of electrometric isolators with low to high stiffness and damping. The results of non-linear time-history analysis on these models show some conservatism in code-specified distribution compared with the observed distribution of story forces. Also a new formula is proposed instead of the triangular distribution to make a better estimation of real behavior of seismic isolated buildings.