Hi, We are planning a KDB on a canal block in SEQ. We have plans to build a single story 270m2 house. Our problem is that due to council flood levels we need our FL roughly 600mm above our original FL (current old house). Prior to hiring a Hyd Engineer, our 1st slab design was going to be 600mm block and back filled slab. But due to the Hyd report (flooding assessment) the block would require too much excavation to compensate for the solid slab added to the block. The team then proposed a steel bearer and joist system that would elevate the house and therefore require no excavation. We have since received estimates on this system ($40K over the original cost of the concrete slab). We are now trying to justify why a steel bearer and joist system would be $40K more then the concrete slab on ground? Has anyone had this experience or would anyone like to share their thoughts on why the the bearer and joist system came in so high? Also what are the pro`s and con`s on both systems?

Note: reason`s for the steel sub floor system instead of timber is that we are in a high termite prone area and on a salt water canal. Our old house we live in has also been home to termites for years!