I am planning to install fiber cement siding over rigid foam sheathing. This is the plan: 2x4 wall, 1/2 OSB sheathing, 2" XPS sheathing, housewrap, and fiber cement siding. The question that I have and am trying to research an answer is, Is it necessary to use vertical furring over the 2" XPS before installing fiber cement siding or can the siding be installed directly over the XPS? The siding will be primed and factory finished on all sides. Thanks.