Deck ledger fastener spacing formula

Need help to understand the ledger fastener spacing formula.
“On-center spacing of ledger fasteners in inches = 100 ÷ joist length in feet”

On a 10 feet long ledger board, how many fasteners should I see?

Have you looked at the decking bible?

My understanding is that a 10 ft. ledger would need fasteners spaced 10 in. apart (100 ÷ 10 = 10).

A 5 ft. ledger would need fasteners spaced 20 in. apart (100 ÷ 5 = 20).

So the number of fasteners should be 12 (120 in. ÷ 10) & 4 (60 in. ÷ 20) in the examples above.

Marcel, the fastener spacing is joist span/length dependent, not ledger length.

It actually is that a ledger supporting 10 ft JOISTS would require fasteners spaced 10 inches apart, or a ledger supporting 5 ft JOISTS would require fasteners spaced 20 inches apart.

It’s a quick estimate of the LOAD being carried on the ledger due to the joists it supports.

Be careful using that math! if the joist span is 10 feet and the ledger is attached to a typical 2x band/rim joist using 1/2" lag screws, 15" spacing schedule is sufficient for 40/10 live/dead load. If a 1/2" thru-bolt is used, the spacing could be almost doubled.

Hey, can you please direct me to the “decking bible”?

That was my understanding, it doesn’t mean I was right.:wink:

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Here are the free graphics I made showing current IRC 2018 requirements:


Great graphics, Randy!..Thanks!

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Randy’s The Best!

Very nice, Randy. Thanks for taking the time to do this!

This is great stuff! Thank you!