We present a model based on continuum elasticity and energy minimization for the study of ferroelastic domain walls close to a surface. We focus on walls orthogonal to the surface, and predict a double-peak structure in the surface values of the squared elastic strain, which is directly related to the chemical reactivity. We also compute the height profile, which can be measured, in principle, e.g. with atomic force microscopy, and the strain distribution in the bulk. Our results are in good agreement with previous atomistic simulations, which had required a much bigger computational effort. The effect of the cubic anisotropy (C₁₂ + 2C₄₄)/C₁₁ on the surface structure of the intersection between the twin wall and the crystal surface is also explored.