I want to attach a beam every 10' to basement wall that's block for the decks we are adding on new construction. basement hole was dug to wide for post unless I set them 6' deep to reach virgin soil. how long does the ledger board need to be for a 4" beam? I hear I need to drill all the way thru the block (8") to support the board. using 2-2"x8"x10' for a 4" beam with post set at 8' and a 2' overhang. deck joist will be 2"x8"x10' 16"oc if they can span that far with the trek deck boards.