on page Inspecting a Deck, Illustrated - InterNACHI is this “rule of thumb”. “On-center spacing of ledger fasteners in inches = 100 ÷ joist length in feet.” This implies to me that for a deck that is 15’ x 15’ the formula would read 100/15=6.67 so for a 15’ ledger you’d need 15x12/6.67=27 ledger fasteners. Is this correct?
then it says there shouldn’t be any in the 5’ at the ends so for the end spacing you’d have to deduct 5" per side so actually the equation would be something like ((15x12)-10)/6.67= 25 ledger fasteners. If this is incorrect, can anyone clarify this for me?