  Given a finite cocommutative Hopf algebra $A$ over a commutative regular ring
$R$, the lattice of localising tensor ideals of the stable category of
Gorenstein projective $A$-modules is described in terms of the corresponding
lattices for the fibres of $A$ over the spectrum of $R$. Under certain natural
conditions on the cohomology of $A$ over $R$, this yields a stratification of
the stable category. These results apply when $A$ is the group algebra over $R$
of a finite group, and also when $A$ is the exterior algebra on a finite free
$R$-module.
