  We use a novel physical space method to prove relatively non-degenerate
integrated energy estimates for the wave equation on subextremal
Schwarzschild-de Sitter spacetimes with parameters $(M,\Lambda)$. These are
integrated decay statements whose bulk energy density, though degenerate at
highest order, is everywhere comparable to the energy density of the boundary
fluxes. As a corollary, we prove that solutions of the wave equation decay
exponentially on the exterior region.
  The main ingredients are a previous Morawetz estimate of Dafermos-Rodnianski
and an additional argument based on commutation with a vector field which can
be expressed in the form
$r\sqrt{1-\frac{2M}{r}-\frac{\Lambda}{3}r^2}\frac{\partial}{\partial r}$, where
$\partial_r$ here denotes the coordinate vector field corresponding to a well
chosen system of hyperboloidal coordinates.
  Our argument gives exponential decay also for small first order perturbations
of the wave operator. In the limit $\Lambda=0$, our commutation corresponds to
the one introduced by Holzegel-Kauffman.
