Deck ledger fastener spacing

DCA6-2015 Table 5 gives seven published connection details across seven joist-span buckets. Read down to your connection and rim joist, across to the joist span the ledger carries, and that cell is the on-center spacing.

Sixteen inches on center is a decking rhythm, not a ledger specification, and it lands on the wrong side of the table at both ends of the range.

Take a 16-foot ledger. Carrying a 15-foot joist span with ½" lag screws into a 1-½" lumber band, Table 5 calls for 11" on center — 19 lag screws. A 16" layout puts in 13. That is 6 fasteners short on the one connection in a deck that has no redundancy — when a ledger lets go, the floor goes with it.

It runs the other way too. At a joist span of 6'-0" or less, a ½" through-bolt into a lumber band is permitted at 36" on center. A 16" habit there drills 2.25 times the holes the code asks for, in the band joist you least want perforated.

The spacing is one cell of a detail. These conditions are printed with the table and govern alongside it.

• The deck ledger must be a minimum 2x8 pressure-treated No. 2 grade lumber, or an approved equivalent.

  DCA6-2015 Table 5 fn.5, p.15

• The tip of the lag screw must fully extend beyond the inside face of the band or rim joist. That governs the screw length; the table does not.

  DCA6-2015 Table 5 fn.1, p.15

• The gap between the face of the ledger and the wall sheathing must not exceed ½".

  DCA6-2015 Table 5 fn.2, p.15

• Lag screws and bolts must be staggered — two rows along the run — per Figure 19.

  DCA6-2015 Table 5 fn.4, p.15

• The ledger must be flashed or caulked so water never reaches the house band joist. Rot behind a correctly bolted ledger fails the connection just as surely as too few bolts.

  DCA6-2015 Table 5 fn.3, p.15

• The stacked-washer detail allows up to a 1" ledger-to-band-joist gap, and is not permitted over gypsum or foam sheathing.

  DCA6-2015 Table 5 fn.7, p.15

• The tabulated LVL values are based on a 300 lb capacity for a 1" LVL rim and 350 lb for a 1-1/8" LVL rim.

  DCA6-2015 Table 5 fn.6, p.15

• A ledger connection also needs a lateral-load connection: hold-down tension devices in not less than two locations, within two feet of the edge of the deck, each with an allowable stress design capacity of at least 1,500 lb.

  DCA6-2015 p.17 [IRC R507.2.4]

Spacing along the run is only half the layout. The two staggered rows also have a minimum end distance from each end of the ledger, minimum edge distances from the top and bottom of both the ledger and the band joist behind it, and a minimum and maximum vertical separation between the rows. Those dimensions live in DCA6-2015 Figure 19, p.15 — the same page as the table — and in IRC Table R507.9.1.3(2).

The ledger and the band joist do not get the same top and bottom minimums, which is exactly why the pattern is staggered rather than mirrored: the upper row is placed for the ledger’s edge distance and the lower row for the band joist’s. Get the spacing right and the edge distances wrong and you have split the very member you are hanging the deck from.

Table 5 is for attaching a deck ledger to a solid wood band or rim joist through sheathing no thicker than 15/32". That is the only case it covers.

DCA6-2015 prohibits prescriptive ledger attachment to brick veneer, stone veneer, hollow masonry, and cantilevered floor overhangs, in the plainest language it uses anywhere: DO NOT ATTACH TO BRICK VENEERS. Attachment to solid concrete or masonry uses expansion or epoxy anchors, which Table 5 does not tabulate. In every one of those cases the honest answer is a designed connection from a licensed professional — or a freestanding deck that never touches the house.

Our sizing engine flags these substrates as DCA6-2015-prohibited-ledger and stops rather than returning a spacing, which is the same thing this page does when you enter a joist span past 18'-0". The reasoning behind those stopping points — the edition, the load basis, and every boundary of the prescriptive method — is set out on our code basis page.

How far apart should deck ledger bolts be?

It depends on the joist span the ledger carries and on what it is bolted to. Under AWC DCA 6-2015 Table 5 (p.15), ½" lag screws into a 1-½" solid-sawn lumber band joist run from 30" on center at a joist span of 6'-0" or less down to 10" on center at 16'-1" to 18'-0". The same lag screws into a 1" LVL rim tighten to 24" and 8" over the same range. There is no single correct number — the spacing is a table lookup.

Is 16 inches on center correct for deck ledger lag screws?

No. A flat 16" is non-conservative for longer joist spans and wasteful for short ones. On a 16-foot ledger carrying a 15-foot joist span, DCA6-2015 Table 5 calls for ½" lag screws at 11" on center — 19 fasteners. A flat 16" layout puts in 13. It errs the other way at the short end: at a joist span of 6 feet or less a ½" through-bolt into a lumber band is allowed at 36" on center, so 16" spacing there drills 2.25 times the holes the table requires.

How many lag screws do I need for a deck ledger?

Divide the ledger length by the table spacing and add one closing fastener at the far end. A 16-foot ledger carrying a 12-foot joist span, using ½" lag screws into a 1-½" lumber band joist, takes 15" on-center spacing — 14 lag screws.

Do deck ledger lag screws have to be staggered?

Yes. DCA6-2015 Table 5 footnote 4 requires the lag screws or bolts to be staggered per Figure 19 — two rows along the run, alternating between an upper and a lower row. The tabulated spacing is measured along the run, from fastener to fastener, not within one row.

What size lag screws does a deck ledger need?

DCA6-2015 Table 5 is published for ½" lag screws and ½" through-bolts only; it gives no values for other diameters. The length is governed by the assembly, not by the table: footnote 1 requires the tip of the lag screw to fully extend beyond the inside face of the band or rim joist. The ledger itself must be a minimum 2x8 pressure-treated No. 2 grade lumber (footnote 5).

Can a deck ledger be attached to brick veneer?

No. DCA6-2015 prohibits ledger attachment to brick or stone veneer, hollow masonry, and cantilevered floor overhangs, and states plainly "DO NOT ATTACH TO BRICK VENEERS" (p.15, p.17). Table 5 covers attachment to a solid band or rim joist only. Attaching to concrete or solid masonry uses expansion or epoxy anchors, which Table 5 does not tabulate, and a deck over any of the prohibited substrates needs a designed connection or a freestanding frame.