IRC Ledger Bolting Pattern

This is a good video on IRC Ledger Bolting Pattern

Nice Perry, Thanks for posting.

It is a good video. The problem is the majority of decks out there will not conform to either pre-2009 or post-2009 IRC standards. I was a carpenter in So CA and Colorado (customs and large tract work) from 1971 to 2003 and never knew that ledger bolting standards existed. There was best practices which was the same in both states and was accepted by the many carpenters I met and worked with over the years.

The best practice that was common during those years in those places was 1/2-inch lags every 24" staggered up and down with two at each break (per ledger) and at the ends.

That’s not a bad formula Kenton. The problem with it is that it doesn’t correspond to load. The potential load on a deck is proportional to its area (the greater the deck area, the more people can be on it at once). The area of a deck is proportional to both it’s joist length (widen the deck and you increase the area proportionally).

InterNACHI’s formula takes potential load into consideration:

Internachi’s ledger fastener spacing formula doesn’t determine the correct spacing between fasteners. It provides a rule-of-thumb that determines a point at which a deck with substantially fewer ledger fasteners may be unsafe by taking potential load into consideration, something most other practices fail to do.

True, but it would depend on the load actually carried by the ledger fasteners, which will vary depending on the understucture design. The forces are both vertical load (fastener shear), and fastener withdrawal.

I’m just saying that anyone calling out a ledger fastened according to what was widespread best practice may get powerful arguments from the agent and seller saying the ledger was fastened according to what was accepted practice at the time in a particular area. Especially in those track homes where you can have 200 homes, 5 models, each with a reverse, and with decks all built the same way.

It’s a lot easier on newer construction that was supposed to be built to code.


Ledger fastening is important because statistically, most fatal deck collapses can be attributed, in part, to ledger fastening. A post failure often causes the deck to twist first and creates a sliding board effect where the occupants then slide off, but where the deck is still partially connected to the house. It’s a slower event. A ledger failure is more instantaneous and often causes the deck to pull from the house on the front posts, thus dropping, or worse, throwing the occupants to the ground.

The other injury-causing defect is the rail. People, by nature, gravitate toward the outer rail of a deck during a party, lean on it, and when it fails, it takes everyone who is leaning on it with it to the ground.