Here the home was built (1974) with a concrete slab about 2 inches below the wood siding. Then the addition of cemented flagstone brought the clearance down to zero in many spots.
Now the question has arisen: are there any exceptions to the 8-inch-above-grade rule, such as installation of a vapor barrier, or if there were some type of drains or drainage canal installed around the edge of the building?
Any cementatious material like that should not be in direct contact with wood siding as it will hold moisture, leading to wood rot. Some form of moisture barrier or flashing should have been used.
Just saw something like this yesterday. That may not be hardiplank exactly but it looks like fiber cement. Here’s a snip from the James Hardi instructions for installation over flat surfaces. You need 1-2”, it looks like. (Why don’t thy just say 2”?! Is it 1” or is it 2”? A minimum shouldn’t be a range of numbers, IMO)