What do I do if only a section of the wall is a parting wall?

If only a section of the wall is a parting wall, for instance, if there is a garage behind half the wall but not the other half, you can split the wall using the blue handles. Simply drag and drop the blue handle to the point where the wall needs to be split. You can then select whether the other side of this wall is a heated or unheated space. In the example, you would select one half of the wall as unheated space and the other as outside.