The ledger connection is where most deck failures start. It is the board that ties the deck to the house, and when it pulls away, the deck comes down with it. The IRC's deck section, R507, spells out how that connection has to be made. Here are the basics a deck builder needs to bid and build it.
Fasteners: lags or bolts, never nails (R507.2)
- Fasten the ledger to a 2-inch nominal band joist with ½-inch lag screws or bolts with washers.
- Space them as the code's ledger fastener table requires. The spacing gets tighter as the joist span gets longer.
- The ledger itself should be at least a 2x8 of pressure-preservative-treated lumber.
- Nails and ordinary deck screws are not permitted for the ledger-to-band-joist connection.
- Fasteners must be hot-dipped galvanized or stainless steel, and lag screw tips must extend fully past the inside face of the band joist.
Flashing, and what you cannot attach to
Flash the ledger (R703.4) so water cannot get behind it into the house rim joist. Hidden rot at the rim is how a sound-looking ledger fails years later. The ledger also may not be attached over exterior veneer such as brick or stucco. Where the wall cannot take a ledger, the usual answer is a freestanding deck on its own beam and posts.
Lateral-load connection (R507.2.3)
Vertical ledger fasteners keep the deck from dropping. A separate requirement keeps it from pulling away from the house: hold-down tension devices at no fewer than two locations per deck, each rated for at least 1,500 pounds, installed in line with the joists and anchored into the house framing. Section R507.2.4 allows an alternative using four devices installed from the exterior. These are separate line items from the ledger bolts.
Guards and their loads (R312.1.1 and R301.5)
Guards are required where an open side is more than 30 inches above the floor or grade below, measured at any point within 36 inches of the edge. Guards and handrails must resist a 200-pound concentrated load applied in any direction at the top, and in-fill openings cannot pass a 4-inch sphere (R312.1.3). Those loads drive post spacing and connection hardware, so guard posts are a hardware line, not just a lumber line.
Permit: an attached deck is not exempt (R105.2)
The model IRC exempts a deck from a permit only if it is 200 square feet or less, no more than 30 inches above grade at any point, not attached to the dwelling, and not serving the required exit door. A ledgered deck is attached, so it fails the third test whatever its size. Local adoptions vary. The Montgomery, Alabama amendment in Ask Donnie's data keeps that four-condition exemption, while other cities remove the deck exemption entirely.
Line items to price on a ledgered deck
- Remove siding at the ledger location and verify the band joist.
- Ledger board, pressure-treated, at least 2x8.
- Ledger flashing.
- Ledger lags or bolts with washers, counted from the spacing table for your joist span.
- Lateral-load hold-down devices, at least two.
- Joist hangers and connectors.
- Footings, posts (for example 6x6) and the beam.
- Joists, decking and fasteners rated for treated lumber.
- Guards and stairs where the deck height requires them.
- Permit and inspections.
Section numbers move between editions
The numbers above follow the 2015 IRC, which the cited library answers use. The deck section was reorganized in 2018 (the lateral-load connection, for example, became R507.9.2), and states and cities amend the code. Confirm with your local building department which edition they enforce before you set the ledger.
Price the connection, not just the boards. Ledger bolts, flashing, hold-downs and guard post hardware are what make the deck stay on the house.