Deck Ledger Fastener Spacing (IRC R507.9)
On-center spacing, fasteners for the ledger length, and a span/table check.
Example
You enter
- Joist span (ft) 15
- Ledger length (ft) 16
- Fastener type lag
You get
- Spacing (in) 11
- Fasteners for ledger 19 (staggered top and bottom rows)
Checked against published worked examples from: Journal of Light Construction (JLC), Deck Builder.
Details, formula, and sources
ScopePer IRC R507.9; the spacing is user-supplied from the adopted table for the fastener/span row.
Formula or tableFastener count = ceil(ledger_length_ft x 12 / on-center spacing) + 1 (no gap exceeds the spacing); spans <= 18 ft are within the IRC table, beyond require an engineered connection.
Source and editionIRC §R507.9 deck ledger connection provisions, by name.
Free accessFree read-only at codes.iccsafe.org; the AHJ-adopted edition governs.
What governsEstimate. AHJ and licensed structural engineer govern.
API field namesjoist_span_ft, ledger_length_ft, fastener, spacing_in, fastener_count
- Spacing user-supplied from the adopted IRC R507.9 table; bolt edge-distance and stagger apply; bottom-of-ledger spacing excludedIRC R507.9