Deck Ledger Board: Size, Bolt Spacing and Flashing, From the DCA6 Table

A deck ledger board is the horizontal piece fastened to the house that carries one side of the deck. Get its size, fasteners and flashing right and the deck stays up. This guide gives you the ledger board size, the lag or bolt spacing for your joist span, how the flashing goes on, and the walls where you cannot use a ledger at all. Every number comes from a row of the free AWC¹ DCA6 deck guide.

What a Deck Ledger Board Does

The ledger carries the vertical load of the deck’s joists on the house side, so the house wall acts as one of the beams. It also ties the deck to the house against sideways movement, in tandem with the hold-down devices.

Why failures happen at the ledger

We have no failure statistics to quote here, and we will not make any up. The weak points are easy to name, though. The load passes through a handful of fasteners into the house band, and any water that gets behind the board sits against that band. A ledger that is too small, fastened too far apart or nailed with the wrong hardware has little margin, and flashing that leaks makes it worse over the years.

What you check first

Before you plan a ledger, look at the wall it will sit on. The band joist must be solid lumber or engineered lumber of a known depth, and the outer wall must not be a type the guide rules out. We cover those walls under “Where a Ledger Is Not Allowed” below.

Deck Ledger Board Size and Material

Size is the easy part, since the guide gives a short rule. The ledger must be at least as deep as the deck joists and no deeper than the house band, and it must be at least a 2x8.

The minimum

In DCA6¹ the ledger is pressure-treated lumber, No. 2 grade, in a size no smaller than 2x8. The same guide asks for joists and rims that carry guard posts to be a 2x8 or deeper, so a 2x8 is the working minimum throughout the deck.

Match the joist depth, stay inside the band

If your deck joists are 2x10, use a 2x10 ledger. That keeps the joist hangers sitting on a full-depth board. The ledger cannot be deeper than the band joist it is fastened to, so a 2x10 band limits the ledger to a 2x10.

Wood treated with copper

Pressure-treated lumber often carries copper in the treatment. The guide says not to use aluminum flashing against copper-treated wood, and it asks for metal flashing at least 0.019 in thick. Pick a flashing metal that is compatible.

Deck Ledger Bolt and Lag Spacing

The spacing table is the heart of ledger design. It lists the distance between fasteners by joist span, for a 1/2 in fastener through up to 15/32 in of sheathing. The fasteners are staggered, one high and one low, along the board.

Lumber band rows, by joist span

Joist span here is the distance the deck joists run from the ledger to the beam. These rows are for a 1-1/2 in lumber band, and the spacing is in inches on center.

Look up the column that matches your joists. A 12 ft joist span with lag screws means a screw every 15 in, and with plain bolts every 29 in.

Engineered lumber and a 2x8 band

If the house band is engineered lumber, the table changes. A 1 in LVL band, with either lag or bolt, runs 24 in at a 6 ft span and 8 in at 18 ft. A 1-1/8 in LVL band runs 28 in down to 9 in. For a house band that is a 2x8 with bolts, the commentary tightens the spacing to 32, 24, 19 and 16 in for spans of 6, 8, 10 and 12 ft. Know what your band is made of before you read a row.

Stagger, edges and ends

Stagger the fasteners so one sits near the top of the ledger and the next near the bottom. The commentary confirms a 2 in distance from the loaded edge. The distance from the ends of the board is in a figure that we could not read in full. Our designer puts the first fastener 4 in from each end, which is our choice and not a published figure, so check what your reviewer wants.

Pilot holes and the fastener tip

Lag pilot holes are 1/2 in in the ledger and 5/16 in in the band, and the screw tip must pass fully through the band. Do not use lead anchors. For a concrete or masonry band, the guide points you to the maker’s instructions for 1/2 in expansion or adhesive anchors.

Deck Ledger Flashing and Siding

Flashing is what keeps a ledger from rotting the wall behind it. Of everything on this page, it is the step most people skip or do halfway.

Take the siding off first

The ledger bolts to the band joist, not to the siding. The guide asks you to remove the siding where the ledger goes, so the board bears on solid framing. Fastening through siding leaves a gap that traps water.

Continuous flashing and a drip edge

The guide asks for continuous flashing with a drip edge over the top of the ledger. The metal should be at least 0.019 in thick, and not aluminum when the lumber is copper-treated. The usual practice, and our advice rather than a DCA6¹ figure, is to lap the wall’s water barrier over the top of the flashing so water runs outward, not behind it.

What to keep out of the joint

Do not fill the gap behind the ledger with sealant and call it flashed. Sealant ages, and water finds the crack. Follow the order in the guide, and ask your building department if it wants a detail drawn for your wall type. Our deck drawings for permit guide shows the ledger and flashing sheet.

Where a Deck Ledger Is Not Allowed

The prescriptive guide rules a ledger out on some walls. If your house has one of them, the answer is a deck that stands on its own posts, or a full engineered plan. The same ledger rules apply to a pergola on the house, with the extra question of whether the wall has a band at rafter height, which our pergola attached to house guide covers. A solid-roof patio cover on the house wall follows the same ledger rules, and our patio cover attached to house guide covers it.

Walls the guide prohibits

DCA6¹ prohibits a ledger on brick or stone veneer, on hollow masonry, on a floor overhang or bay window, on a truss ribbon board, and on an I-joist band less than 1 in thick. A veneer wall cannot carry the load, and a cantilever or ribbon board was not built for it.

The alternative: a freestanding deck

A freestanding deck carries all its own weight on a second beam and posts beside the house. DCA6¹ does not give a lateral table for that, since it assumes the house resists the sideways load. Our designer allows a freestanding deck up to 8 ft high with knee braces both ways at the corner posts, and blocks anything higher. That limit is our design choice. Read the DCA6 explained guide for what the guide leaves out.

When to ask an engineer

If your wall is on the prohibited list and you want it attached, the deck falls outside the tables, and a reviewer may ask for a stamped design. We prepare plans to DCA6¹ and IRC R507 prescriptive tables, not engineer-stamped. Check with your building department.

Lateral Load Devices at the Ledger

A ledger carries weight, but sideways forces need their own connection. These are the hold-down devices, and they sit near the ledger on the deck edge.

The DCA6 rule

For an attached deck, the guide calls for two hold-down tension devices rated at least 1,500 lb within 2 ft of the deck edges. The wall they attach to needs 3/8 in panel sheathing, and the devices cannot go into brick veneer.

The 2021 county alternative

Two county guides that use the 2021 IRC show a different option: four devices rated at least 750 lb. We use the DCA6¹ version in our designer. If your county prints the four-device version, show it on your lateral sheet. Check with your building department.