The figure below depicts the basic structure of a single or multi-family house.
Additional walls can be added if further differentiation is necessary.
The vertical walls are assumed to be the same in the whole building.
Source: Schulte, Lukas. April 2019. „Model implementation and simulation of a multi-family house of different levels of detail for evaluation in hardware-in-the-loop experiments“. RWTH Aachen University, E.ON Energy Research Center, Institute for Energy Efficient Buildings and Indoor Climate.