The boundary wall method (BWM) is a general purpose procedure to treat boundary value problems for wave equations, specially Helmholtz’s (the case addressed here). Similarly to most protocols for boundary value problems, the BWM may be computationally demanding for large borders C, at which the wave function must satisfies determined boundary conditions. Also, although an exact approach, it is rarely amenable to closed solutions. The BWM employs the Green’s function G 0 of the embedding domain V of C. However, in many instances — like for C modeling a billiard — the specific V is not really fundamental and thus one has a certain freedom to choose distinct domains and so G 0 ’s. Here we consider this characteristic of the BWM and show how to obtain some analytical results and solve numerically semi- infinite waveguides by exploring proper Green’s functions. Explicit calculations for Dirichlet and leaking boundaries for rectangular, triangular and trapezoidal structures are presented as well as scattering states within semi-infinite rectangular waveguides.