A recently completed extension to IEA BESTEST includes further work on tests suitable for the validation of ground coupled heat transfer modules within building energy simulation software. The model described here forms part of this work. A finite difference model was prepared and applied to ground coupled heat transfer in the environs of a building for a range of geometries and boundary conditions. The model was verified by demonstrating close agreement with an analytical solution and with two independent models; it is therefore fit for purpose. A fundamental modelling limitation, applying to ground coupled heat transfer, emerged from the work.