Some building departments also publish their own codes which may differ somewhat from the IRC. Decks not connected to ledger need not have footings extending below frost line. 18.12 Allowable Glazing Materials. The span table used in our area for 2011 is the UBC 1997 code (left) for the minimum size of joists for decks. Fire resistant exterior siding 4. 9.4 Girders for single-story construction or supporting one floor shall be 4 by 6 inch for spans 6 feet or less, with girders spaced at 8 feet on center. Ledger board width must be => deck joist width but =