Attaching a ledger board - only partial rim joist

Question

Last year I removed the rotting deck that was on the back of my house and this year I am replacing it. The previous ledger board was bolted directly against the shingles in the position indicated by the red lines. I was intending to place the new one in the same location.

Today I planned to attach the flashing and ledger board. I removed a double-layer of cedar shingles, the tar paper beneath them and the fiber board under that - and was surprised to discover I was looking into my house. I moved further and found a rim joist that covers part of the floor joists, although it doesn't look particularly sturdy and is between the joists rather than capping them.

Any thoughts on how I should proceed?

I can remove further shingles, but I didn't want to make the hole bigger until I had a better understanding of what to do.

Answer 1

The way I see it, you have two options to make things correct:

1. put blocking between them and a header joist over them to tie it together (It would be the equivalent of a 1-1/2 inch cantilever). But you'd have to deal with siding over the little bump-out
2. cut back the joists 1.5 inches and put in a rim joist and splice it to the other joist with a tie plate. Cutting back the joists will be a real pain.

I'd be tempted to just put in the blocking and sheet over it with something pretty good like half inch laminate, however I'm pretty sure that wouldn't pass an inspection.

Answer 2

Is that basement behind there? It looks like there's an oil tank. How did you fill the tank when the deck was there? If that was my house I think I'd put some kind of joist blocking/bracing in everywhere there isn't any deck or no deck. Under the circumstances free-standing would probably be the better plan. Why aren't you placing the deck level with the inside floor?

Answer 3

Under the International Residential Code (IRC), a rim joist substitutes for lateral blocking. See IRC R502.7. In the absence of a rim joist you should install blocking (or a rim joist). There's a prescribed nailing schedule at item 15, 23, 27, and 30 under IRC R602.3. The purpose of the rim board or blocking is to prevent all of the joists from flopping over sideways all at once under a wind or seismic load.

Attaching a ledger below the plane of the floor can be a problem under the IRC's deck ledger details. Those details all show fasteners anchored in the rim joist and fix fastener location constraints, where your ledger's bottom lag screws may miss the rim board. When arguing with the inspector, just remember that these details are dictated under the IRC's "vertical supports" section. A lag screw in a wall stud below the rim joist has the same load path down to the foundation that the rim board lag screw had. IRC R507.9.1.4 invites arguments like this.

Following IRC R507.9.2, you also need special purposed lateral support to prevent the deck from pulling away from the structure. The stagger in your ledger's elevation looks like ordinary deck tension ties will work.