How should I prepare my wall and mount a deck ledger to it?

Question

I'm replacing a deck that the previous owner installed because it was sagging. When I pulled the old ledger board, I realized it wasn't really anchored well to the rim joist at all. Upon further inspection it seems that the stack up is odd - it seems the rim joist was only covered with 1/2 rigid foam, then T1-11 for sheathing, then the vertical panel siding. Some of the sheathing is a bit rotted and came off with the old ledger.

How should I go about waterproofing this? I got some flat back flashing and some z flashing, but does the back flashing go under the foam? Do I need to repair the sheathing? Should I cut the sheathing and foam and just lag the ledger directly to the rim joist? This is in Midwest USA, so rain and freezing/thawing are issues.

Answer 1

How should I go about waterproofing this?

Really, the only flashing would be under your siding (and any water barrier membrane, which you don't have). Z-metal over the old siding and over the ledger should do. If you want to protect the original siding, rim, etc., you could apply a rubber flashing to that entire area, under the Z-metal and the new ledger, as in the example you posted.

Does the back flashing go under the foam?

Putting flashing behind the foam leaves the foam vulnerable. That wouldn't be appropriate.

Do I need to repair the sheathing?

Probably not, unless you have a splice or mounting hardware right there. Two-by lumber should span that little gap without issue. Otherwise just fill it roughly with whatever half-inch scrap you have around.

Should I cut the sheathing and foam and just lag the ledger directly to the rim joist?

Lagging to the rim is no longer considered a valid way to mount a rim joist due to failures. Many jurisdictions will fail inspection over that. Instead, look for appropriate building hardware, such as through bolts or dedicated hangers. What you choose will determine whether you need to remove the foam, since it's compressible.