It has just occurred to me why do we commonly sit FFL's 150mm above floor level just because DPC is at this level? Is there a reason we don't use have outside dpc higher than inside especially in cavity wall construction? Is this not what we invariably do anyway around the level access opening? Also is this why bottom of timber frames are not level with FFL so no timber in splash zone at level access? Your never going to get the bottom of a suspended floor anywhere near ground level without house sitting 600mm high once beams insulation and screed is accounted for.
Excuse me if i'm being stupid it just occurred to me every house seems to be 6" above ground, even when no local risk of flooding.