Q: I need to attach a deck to a home with an I-joist floor system. Can I attach the ledger to the engineered-wood rim joist?
A: Mike Guertin, a builder and remodeler in East Greenwich, R.I., and a presenter at JLC Live, responds: If the rim joist is structural—in other words, designed to transfer compression loads between the subfloor sheathing and the mudsill or plate below—then a deck ledger can be attached to it. The American Wood Council's "Prescriptive Residential Wood Deck Construction Guide" (DCA6) contains a prescriptive ledger-fastening table (Table 5), similar to the one in the IRC, that includes spacing requirements for attaching a deck ledger to 1- or 1 1/8-inch engineered-wood rim boards with 1/2-inch lag screws and 1/2-inch through-bolts. Manufacturer prescriptive ledger tables for proprietary structural ledger screws—such as FastenMasterLedgerLok, Simpson Strong-Tie SDWH and SDWS, and GRK RSS — also list engineered rim-board types. Most building officials will accept the DCA6 as well as manufacturer's tables for connecting ledgers to an engineered rim board.
But not all engineered floors are framed with structural rim boards. When I was framing floors with I-josts in the late 80s, engineered rim board was not available, and we closed the rim with either an I-joist or 3/4-inch plywood ripped to the I-joist height. Deck ledgers cannot be attached to these I-joists or nonstructural plywood rims. If you can view the rim board from inside the house, you may be able to find spray-on labeling that identifies it as structural. Otherwise, to determine whether a rim joist is structural, drill a 1-inch-diameter hole—in a location that can be flashed over if needed—all the way through the rim board to ascertain its thickness. If it is 1 inch or 1 1/8 inches thick, it's considered structural and you can proceed with fastening the ledger according to the tables mentioned above. If the rim closure is nonstructural, however, the simplest solution is to construct a freestanding deck—set footings, posts, and a beam 1 foot or so from the house to bear the deck load ordinarily carried by a ledger. If a freestanding deck is not a viable option, the best alternative is to have an engineer design the ledger attachment, and have that approved by your local official.