  We study the influence of sample termination on the electronic properties of
the novel quantum spin Hall insulator monolayer $1T'$-WTe$_2$. For this
purpose, we construct an accurate, minimal 4-orbital tight-binding model with
spin-orbit coupling by employing a combination of density-functional theory
calculations, symmetry considerations, and fitting to experimental data. Based
on this model, we compute energy bands and 2-terminal conductance spectra for
various ribbon geometries with different terminations, with and without
magnetic field. Because of the strong electron-hole asymmetry we find that the
edge Dirac point is buried in the bulk bands for most edge terminations. In the
presence of a magnetic field, an in-gap edge Dirac point leads to exponential
suppression of conductance as an edge Zeeman gap opens, whereas the conductance
stays at the quantized value when the Dirac point is buried in the bulk bands.
Finally, we find that disorder in the edge termination drastically changes this
picture: the conductance of a sufficiently rough edge is uniformly suppressed
for all energies in the bulk gap regardless of the orientation of the edge.
