Previous models of the surface structure of ferroelastic domain walls have neglected one potentially important consideration. This is the effect of a volume strain coupled to the order parameter. Such a coupling affects the structure of the domain wall both in the bulk and at the surface. In the bulk only certain components of the strain tensor can relax in response to the stresses generated within the domain wall by this coupling without disrupting the continuity of the lattice. However, at the surface a more general relaxation is possible. This has an asymmetric effect on the domain wall surface structure, causing it to widen at one surface and narrow at the opposite surface.