A deck ledger is the board bolted to the house that carries half the deck's weight, and its fasteners carry that weight in shear while resisting the deck's constant attempt to pull away from the building. Ledger failure is the classic catastrophic deck collapse: the deck peels off the house with people on it. Fastener type, size, and spacing are the engineering that prevents it, and they follow from the loads with no room for improvisation.
What loads the fasteners see
Ledger fasteners handle two demands at once. Gravity loads from the deck, people, furniture, snow, bear down on the ledger and load the fasteners in shear. Lateral loads, the deck racking and pulling away from the house, load them in withdrawal and tension. The spacing rules in building codes account for both, which is why ledger fastening schedules look denser than intuition suggests: they are not just holding the board up, they are holding the deck to the building.
The total load grows with the deck's tributary area, the portion of the deck whose weight the ledger supports. Deeper joist spans mean more tributary area, more load per foot of ledger, and tighter fastener spacing. Long spans do not just need bigger joists; they need more ledger bolts.
Fastener types that qualify
Through-bolts with washers, hot-dip galvanized or stainless, are the traditional gold standard: they clamp the ledger to the house framing with positive, inspectable connection. Structural lag screws of adequate diameter, properly installed into solid framing, are the common modern alternative. Proprietary structural screws rated for ledger applications offer a third option, with manufacturer-specified spacing that must be followed exactly.
What does not qualify: nails, deck screws, or any fastener not rated for the structural loads involved. The ledger is structural framing, and its fasteners are structural fasteners. Corrosion resistance is mandatory; a ledger bolt that rusts through in a decade is a delayed failure. Match the fastener metal to the flashing and treatment chemicals, since dissimilar metals and corrosive treatments eat fasteners.
Spacing rules and edge distances
Code-prescribed spacing patterns stagger fasteners in two rows along the ledger, with spacing that tightens as joist span increases. A typical pattern might call for fasteners every 16 inches on center in a staggered arrangement for moderate spans, tightening for longer spans. Follow the code table for your joist span and load; do not interpolate casually or extend spacing because the pattern looks dense.
Edge distances matter as much as spacing. Fasteners too close to the ledger's top or bottom edge split the board; too close to the ends split it lengthwise. Maintain the code's minimum edge and end distances, pre-drill pilot holes to the correct diameter, and stagger the rows so fasteners do not line up in a single splitting plane. A split ledger at a fastener line has lost that fastener entirely.
What the ledger fastens to
Fasteners are only as good as what they bite into. The ledger must attach to solid structural framing: the house's rim joist, wall studs, or concrete foundation, never to siding, sheathing, or brick veneer alone. Each of those substrates has its own fastening requirements and spacing rules; a ledger bolted to sheathing is decorative, not structural.
Verify the substrate before laying out the pattern. Probe or open up to confirm rim joist location and condition, especially on older homes where the rim may be undersized or deteriorated. Rotten or undersized framing behind a new ledger is a failure waiting for a party.
Flashing: the fastener's bodyguard
Water is the ledger's slow enemy. Flashing above the ledger directs water out over the board instead of behind it, where trapped moisture rots the ledger, the house framing, and the fasteners' substrate. Install metal flashing tucked under the siding and over the ledger top before the ledger goes up, and never rely on caulk as the primary water defense.
Inspect flashing and fasteners as maintenance, not just at construction. Look for rust streaks, soft wood at the ledger line, and fasteners that have loosened. A deck's ledger connection should be re-examined every few years; the fasteners you cannot see are holding up the deck you stand on.
Ledger fastening is structural work with life-safety stakes: rated fasteners, code spacing for your span, proper edge distances, solid substrate, and flashing that keeps it all dry. Size it by the book, install it carefully, and inspect it periodically. The deck stays attached to the house, which is the entire job.
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