I want to build a new wooden or vinyl deck over an existing concrete deck and hoping to do so without removing any existing concrete. The original deck must not have had proper footings installed because the deck slopes towards the house…. causing all water run off to drain towards the house and cyclically increases the slope with time. There’s enough space, between the top of the old concrete deck and the new proposed deck to include support joists, that won’t interfere with the entry way but I will still need to place some type of material between both decks that is rigid enough to be sloped and act as a water buffer…any ideas?