I simply want to know how many bolts I need to put in per foot, and how they're spaced. The ledgers for each house floor are 2x8s with joists every 1'.

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Unless you're talking about a deck (where you can find details on ledger fastening in the International Residential Code), you hire an approved source as defined by a building official with jurisdiction over your project.

The approved source would need the specifics of your structures, old and new, and he would follow the prescriptions of the IBC to compute an anchoring layout based on sources from outside the code. There is no table (unless this is a deck) in a common code for ledger fastening. That anchoring layout will depend on the loads, the adequacy of what I assume are bearing walls, the particular fasteners, geometry of the connections, and on and on.

You couldn't possibly believe that you've provided sufficient information for anybody to compute a legitimate layout. An approved source must carry insurance to compensate you if his specifications result in injury or death. You shouldn't trust people on the internet with nothing at stake to provide such specifications.

Lots of similarly detailed decks were falling off of houses. That's why there are deck ledger details in the International Residential Code (see https://awc.org/codes-and-standards/is-your-deck-safely-connected-to-your-house/). There aren't tables for every scenario, just the very, very common scenarios. If you have an adventurous building official, then he might acknowledge that decks and your add-on have the same live load and loading conditions (if they have the same loading conditions), letting you use the IRC's deck ledger tables. I'm skeptical that you'll find a building official like that.


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