Deck Ledger Attachment: The Two Jobs the Code Asks It to Do
By Seamless Home Team, Home services operations · September 22, 2026
Quick answer
The residential code treats a deck ledger as two separate obligations. Vertical support is the fastener schedule: half-inch lag screws or bolts in two staggered rows, spaced on centre according to the joist span and the fastener type, from 30 inches apart at a 6-foot span down to 10 inches at an 18-foot span. Lateral connection is a different requirement met by rated hardware — either two devices rated at not less than 1,500 pounds within 24 inches of each end of the deck, or four devices rated at not less than 750 pounds. Fasteners carry the deck's weight down; lateral devices resist it pulling away from the house, and a ledger can be perfectly fastened and still have no lateral connection at all. Before any of that applies, three conditions have to be true: the ledger may not be supported on stone or masonry veneer, the band joist behind it must be solid-sawn 2-inch nominal lumber or an approved engineered rim board bearing fully on the structure, and the ledger may not carry concentrated loads from a beam or girder. Where any of those fails, the prescriptive tables do not apply and the connection has to be engineered.
Almost every deck that comes off a house comes off at the ledger, and almost every investigation of one finds fasteners that were the right size, in the right number, in roughly the right places.
That is not a contradiction. It is a description of what the code actually asks for, and of the half of it that gets built. Section R507.9 of the residential code gives the ledger two separate obligations, and they resist two different forces. Meeting one of them perfectly does nothing for the other.
The two jobs
| Vertical support | Lateral connection | |
|---|---|---|
| What it resists | The deck's weight pressing down | The deck moving away from the house |
| How it is met | A schedule of half-inch lag screws or bolts in two staggered rows | Rated hardware: 2 devices at ≥1,500 lb within 24 in of each end, or 4 devices at ≥750 lb |
| Where the numbers live | Table R507.9.1.3(1), keyed to joist span | R507.9.2 |
Vertical support is the part everyone builds, because it is the part that looks like attaching a board to a wall. Lateral connection is hardware with its own load path running back into the floor framing inside the house, and it is the part that gets value-engineered out of a deck by someone who looks at a row of half-inch lags and concludes the ledger is well attached.
A row of half-inch lags is well attached, in shear. It is not a lateral connection, and the code does not treat it as one.
Three conditions that void the table before you reach it
The fastener schedule is prescriptive, which means it comes with the conditions under which it was derived. Three of them disqualify a great many real walls, and each one sends the connection to an engineer rather than to a table.
The middle one is worth sitting with, because it is invisible. Nobody opens a wall to identify a band joist before pricing a deck. The result is a ledger bolted to whatever is behind the sheathing, on the assumption that a house has a band joist everywhere a deck might go. Where the floor above cantilevers — a bump-out, a bay, an overhanging second storey — the rim at that point is carrying itself out past the foundation and is not bearing fully on anything.
The spacing is a function, not a number
The most common error on a correctly conceived ledger is a single remembered figure applied to every deck. The table is keyed to three variables at once: the span of the joists bearing on the ledger, what the fastener is, and how thick the sheathing is between the ledger and the band joist.
| Joist span | ½ in lag screw | ½ in bolt, ≤½ in sheathing | ½ in bolt, ≤1 in sheathing |
|---|---|---|---|
| 6 ft and less | 30 in | 36 in | 36 in |
| 6 ft 1 in – 8 ft | 23 in | 36 in | 36 in |
| 8 ft 1 in – 10 ft | 18 in | 34 in | 29 in |
| 10 ft 1 in – 12 ft | 15 in | 29 in | 24 in |
| 12 ft 1 in – 14 ft | 13 in | 24 in | 21 in |
| 14 ft 1 in – 16 ft | 11 in | 21 in | 18 in |
| 16 ft 1 in – 18 ft | 10 in | 19 in | 16 in |
On-centre spacing from Table R507.9.1.3(1). Read across, not down: at a 14-foot joist span, lag screws go in at 11 inches and bolts at 21, and the deck with bolts is not under-built — it is a different fastener with a different capacity.
Two details in the same table decide whether the spacing means anything:
- Fasteners must be hot-dipped galvanized or stainless steel. Pressure-treated lumber is corrosive to ordinary fasteners, and a deck ledger is wet lumber held on by metal.
- Lag screws and bolts are staggered top to bottom along the run, in two rows, with a minimum 1⅝ inches between rows, not less than 2 inches from the top edge, not less than ¾ inch from the bottom edge, and not less than 2 inches from the ends. A single row at the mid-height of the ledger is the wrong pattern regardless of how many screws are in it.
Two drill bits, one screw
This is the detail that lets a correctly specified and correctly spaced connection fail anyway, and it takes about fifteen extra seconds per fastener to get right.
A half-inch lag screw needs two different holes:
- Half an inch through the ledger and through any sheathing, so the shank passes through freely and the head can draw the ledger tight to the wall.
- 5/16 to 3/8 inch continuing into the band joist, so the threads have wood to cut and can develop withdrawal resistance.
Drilling one half-inch hole all the way through is faster and it removes most of what holds the deck onto the house. The code adds two more conditions in the same breath: the tip of the lag screw must fully extend beyond the inside face of the band joist, and the screws must be full-body diameter rather than reduced-shank. A screw that is the right diameter, in the right place, at the right spacing, can still be short.
The flashing failure is slower and just as final
The ledger creates a horizontal ledge and a row of penetrations against the house, at the elevation where water runs down the wall. The code requires it to be flashed so water does not reach the house band joist — corrosion-resistant metal flashing, or an approved non-metallic material compatible with the substrate and the decking, integrated with the wall's water-resistive barrier.
An unflashed ledger does not fail on the day it is built. It fails several years later, and by then the fasteners are still correctly sized and correctly spaced, anchored into a band joist that has stopped being structural lumber. The inspection that would have caught it happened before the water did anything.
A note on the section number
If you have looked this up before and found it under R507.2, you were not reading an obsolete document. The deck ledger connection to band joist sat at R507.2 in older editions with its spacing table as Table R507.2; in current editions the same material sits at R507.9, with the ledger-to-band-joist detail at R507.9.1.3 and the table as Table R507.9.1.3(1).
The numbers in the table did not change. Only the address did. That is worth knowing because the usual reaction to a citation that does not resolve is to assume the requirement was revised, and here it was not — which means an old plan detail referencing R507.2 is describing the same connection the current code describes, and a jurisdiction citing R507.9.1.3 is not asking for anything new.
What this means before you build
Three questions, in order, and only the third one is about fasteners:
- What is behind the sheathing where the ledger lands? If the answer is veneer, or a cantilever, or "we'll find out," the prescriptive path is not available and that is a design decision, not a field decision.
- What is providing the lateral connection? If the answer is the lag screws, there is no lateral connection. It is a separate line item with separate hardware and it belongs in the quote.
- What is the joist span? That is what sets the spacing, along with the fastener and the sheathing thickness.
You can work through all three, plus the drilling, staggering and edge-distance requirements, in the deck ledger connection checker, which will tell you when the prescriptive tables have stopped applying rather than giving you a spacing that does not govern.
The bottom line
The ledger is the one connection on a deck where the code declines to let you use your judgement, and it declines twice: once on what carries the load down, and once on what stops the deck leaving. Most ledgers answer the first question well. The second question is answered by hardware that has to be bought, specified and installed on purpose, and the reason ledger separations look so uniform in photographs is that it usually was not.
If a deck is part of a larger project and you want the permit path, the inspection sequence and the trades sorted before anything is fastened to the house, tell us what you are planning. Coverage is confirmed per service area rather than promised as blanket availability.
Frequently asked questions
How far apart do deck ledger bolts go?
There is no single number, which is the most common source of error on this connection. The on-centre spacing comes from a table keyed to three things at once: the span of the deck joists bearing on the ledger, whether the fastener is a half-inch lag screw or a half-inch through bolt, and the thickness of the sheathing between the ledger and the band joist. For half-inch lag screws the spacing runs from 30 inches on centre at a joist span of 6 feet or less, to 15 inches at a 10-to-12-foot span, to 10 inches at a 16-to-18-foot span. Half-inch through bolts are permitted to sit further apart because they carry more: 36 inches at the short spans, narrowing to 19 inches at 16 to 18 feet with half-inch maximum sheathing, and to 16 inches where the sheathing is up to 1 inch. Using one remembered figure across every deck produces a connection that is correct for exactly one span.
Can a deck ledger be attached to brick or stone veneer?
No. The code states it directly: deck ledgers shall not be supported on stone or masonry veneer. Veneer is a cladding, not a structural element, and it is not tied to the frame in a way that can carry a deck. This is the single sentence that voids the most common retrofit assumption, because the veneer is what is visible and it looks substantial. The compliant approaches are to remove the veneer locally and land the ledger on the structural band joist behind it with an engineered detail for the resulting gap and the through-fastener length, or to avoid the connection entirely with a freestanding deck carried on its own posts and footings. Both are decisions for the design stage rather than the day the ledger goes up.
What is the difference between ledger fasteners and a lateral load connection?
They resist different forces and neither substitutes for the other. The fastener schedule resists the deck's vertical load — everything on the deck pressing down, transferred through the joists into the ledger and from there into the house framing. The lateral load connection resists the deck moving away from the building, which is what actually happens when people move together on a deck and what ledger separations look like after the fact. The code gives two compliance paths: devices rated at not less than 1,500 pounds installed at not fewer than two locations per deck, within 24 inches of each end, or devices rated at not less than 750 pounds at not fewer than four locations. These are rated hardware items with their own load path back into the floor framing, not more lag screws. A ledger with a textbook fastener pattern and no lateral devices is not a compliant ledger.
Why does a half-inch lag screw need two different drill bits?
Because the two pieces of wood have opposite jobs. The hole through the ledger and through any sheathing is drilled at the full half-inch, so the screw shank passes through without binding and the head can draw the ledger tight against the wall. The hole continuing into the band joist is drilled smaller, between 5/16 inch and 3/8 inch, so that the threads have wood to cut into and develop withdrawal resistance. Drilling one half-inch hole straight through is quicker and it removes most of what holds the deck on. The code also requires that the tip of the lag screw fully extend beyond the inside face of the band joist, and that the screws be full-body diameter rather than reduced-shank, so a screw that is correctly sized and correctly spaced can still fail on penetration depth alone.
Does the band joist behind the ledger have requirements of its own?
Yes, and they are easy to miss because the band joist is hidden. It has to be a minimum 2-inch-nominal solid-sawn spruce-pine-fir or better, or an approved engineered rim board, and it has to bear fully on the primary structure and be capable of supporting all required loads. The phrase that does the work is bear fully. A cantilevered floor, where the rim sits out past the foundation rather than over it, does not satisfy it, and neither does a rim of unknown composition behind a finished interior. The ledger is also not permitted to carry concentrated loads from a beam or a girder — it is sized for uniformly distributed joist loads, and a beam landing on it is a different structure than the table describes.
Why do I find deck ledger rules under R507.2 in some places and R507.9 in others?
Because the section was renumbered, not rewritten. Older editions of the IRC carried the deck ledger connection to band joist at R507.2 with its spacing table as Table R507.2. In current editions the same material sits at R507.9, with the ledger-to-band-joist detail at R507.9.1.3 and the spacing table as Table R507.9.1.3(1). The numbers in the table did not change. This matters practically, because a contractor or inspector working from a remembered section number can conclude that a correct reference is obsolete, or hunt for a revision that never happened. Check the section against the edition the local jurisdiction has adopted rather than against the number you remember.
Does a deck ledger have to be flashed?
Yes, and the flashing is a code requirement rather than a best practice. The ledger is fastened through the wall covering into the band joist, which puts a horizontal ledge and a row of penetrations directly against the house at the point where water runs down the wall. The code requires the ledger to be flashed so that water does not reach the house band joist, using corrosion-resistant metal flashing or an approved non-metallic material compatible with the substrate and the decking, integrated with the wall's water-resistive barrier. Rot behind an unflashed ledger is the quiet version of this failure: the fasteners remain correctly spaced and correctly sized while the wood they are anchored into stops being wood.