Best Practices: Decks - Ledgers
As a Northern Utah Home Inspector, I find that the attachment of deck ledgers is of utmost importance in the prevention of deck failures, death, and injuries. This is another segment in a series provided by the Journal of Light Construction trade magazine, and while all of the information presented isn’t mandated by the building codes, several of the specifics greatly exceed the code and this is why they are deemed “Best Practices”. If you are going to build a deck, or have one built, then I highly recommend that you take the safer “Best Practices” approach. It may cost more on the initial investment of the build, but the “Best Practices” detailing will provide years of trouble free peace of mind while you enjoy time on your deck.
Journal of Light Construction (JLC) - Deck Ledgers
Improper sizing and fastening of the ledger board is the single biggest cause of deck failures. The details show methods for fastening the ledger to the band joist directly or through sheathing, with either lag screws or bolts. Also shown are flashing and spacing details that promote drainage and protect the structural members and fasteners from moisture.
In the best case, the ledger is through-bolted to a band joist, and the band joist is laterally braced to other components in the floor frame of the primary structure (see Bracing). When this isn’t feasible, other methods are available (see Ledger Support Alternatives).
Solid-sawn two-by, preservative-treated southern pine or hem-fir is typical for ledger boards. A ledger should be a minimum of 6 inches deep and at least the same thickness as the deck joists. Choose the straightest board available or a deck ledger.
Ledger Fastener Placement
Fasteners should be hot-dipped galvanized or stainless steel and staggered along the ledger face according to code (see illustration and tables). Make sure that ledger fasteners won’t fall on the joist layout. Fasten through any spacers used to hold the ledger off the sheathing.
Structural fasteners are available that meet or exceed the shear design values of 1/2-inch lags. They typically come either coated or in stainless steel, require no pre-drilling, and can be driven with an impact driver or a 1/2-inch drill at low speed. Manufacturers provide size and spacing charts that will meet code, depending on the materials used and the maximum joist span of the deck.
Notes: The tip of the lag screw should fully extend through the inside face of the band joist. The maximum gap between the face of the ledger and the face of the wall sheathing is 1/2 inch. Flash the ledger to prevent water from contacting the band joist. Stagger lags and bolts (see LOCATE illustration). Deck ledger should be minimum 2x8 PT #2 grade lumber or other approved material. When fastening solid-sawn PT ledgers to 1-inch-thick (min.) engineered rim joist, use an engineered attachment. Wood structural panels, gypsum boards, or rigid foam are permitted as sheathing; the maximum distance between the face of the ledger and the face of the band joist/rimboard is 1 inch.
Ledger Support Alternatives
Where access to house floor framing is uncertain, supporting the ledger with posts offers a sound solution (see illustration). Another alternative to connecting a ledger to the band joist is to build a freestanding deck. In this case, it is critical to anchor posts to piers to prevent uplift (see Connections), and to brace all posts in both directions, as shown. To prevent racking of deck joists, use diagonal bracing fastened to the underside of the framing members.
Supporting a ledger with posts is a good option when a deck is to be built next to a brick-veneer, stucco, or concrete wall. A strong post-to-beam connection and through-bolting to the wall provide resistance to lateral forces. Where posts bear on below-grade footings, use treated lumber rated for use in permanent wood foundations and structural building poles.
Michael Chotiner is a contributing editor to JLC.