Deck Ledger Board: Size, Bolt Spacing & Flashing

What a deck ledger board is

A ledger board is the length of lumber fastened flat against the house that carries the deck’s inner end; the joists hang from it in hangers. The 2021 IRC makes it at least a 2x8 nominal, of pressure-treated southern pine, incised pressure-treated hem-fir or approved naturally durable lumber, No. 2 grade or better.

Two limits come with it: a ledger may not carry the concentrated load of a beam or girder, and it may not be supported on stone or masonry veneer.

Ledger bolt and lag screw spacing

The code spaces half-inch fasteners by the length of the joists the ledger carries: longer joists put more of the deck on each foot of ledger, so the fasteners move closer. It gives three columns: lag screws through no more than half an inch of sheathing, bolts through half an inch, and bolts through up to an inch.

A 16-foot ledger carrying 12-foot joists takes lag screws no more than 15 in apart, starting 2 in from each end: that is 14 lag screws, or 8 bolts at 29 in.

The fasteners are hot-dipped galvanized or stainless steel. A lag screw’s tip must pass fully beyond the inside face of the band joist. The half-inch columns allow wood structural panel or solid lumber sheathing; the one-inch bolt column also allows gypsum board, fiberboard and foam, and up to half an inch of stacked washers can stand in for sheathing.

Snow loads

Where the fasteners go

The code sets minimum distances from each edge of both boards, and the fasteners stagger from the top to the bottom along the ledger.

Deck ledger flashing

The code requires approved corrosion-resistant flashing where a deck attaches to a wood-frame wall, lapped shingle-fashion so water cannot reach the wall cavity or the framing, and carried out to the face of the wall finish. The ledger table repeats it: flash the ledger to keep water off the house’s band joist.

Metal flashing must be corrosion-resistant and at least 0.019 in thick. Vinyl or other plastic flashing has to be an approved nonmetallic material compatible with the house and the decking, and flashing tape, a self-adhered membrane, must meet AAMA 711.

Deck rim joist and the house band joist

The ledger fastens to the house’s band joist, the board that rims the house floor. It must be 2-inch nominal solid-sawn spruce-pine-fir or better, or an engineered rim board at least 1-inch nominal, bearing fully on the house structure.

At the deck’s outer edge, the rim joist across the joist ends keeps them from rolling. Fasten it to each joist end with three 10d nails or three No. 10 wood screws 3 in long; joist hangers or blocking used instead must be at least 60 percent of the joist depth.

Tying the deck to the house sideways

The ledger carries the deck’s weight; a separate connection keeps the deck from pulling away. The code’s two options are hold-down tension devices in two places within 24 in of each end of the deck, each rated for at least 1,500 lb, or in four places at 750 lb each.

Brick, stone and other walls

Because a ledger may not hang on stone or masonry veneer, a deck beside a brick-veneer wall needs another way to carry its house side. The code allows other framing that meets the R301.5 loads; one route is a beam on posts along the wall, sized from the deck beam span chart.

Deck ledger board FAQ

Sources & method

1. International Code Council. 2021 IRC Chapter 5 Floors, Section R507 Exterior Decks. 2021 IRC
2. International Code Council. 2021 IRC Chapter 7 Wall Covering (Section R703.4 Flashing). 2021 IRC