A deck ledger has to be positively attached to the house with the bolts or lag screws the code calls for, in the pattern the code calls for, with flashing to keep water out, never with nails alone. Nails-only ledger attachment is prohibited, and it is the single biggest reason decks collapse. The exact fastener size, spacing, and edge distances are set by the code edition your jurisdiction adopted, so this guide teaches how a ledger connection has to work and routes the numbers to your AHJ. A ledger failure is not a leaky-corner problem, it is the whole deck pulling off the house with people on it, which is why the code is strict and inspectors do not bend on it. Understand the connection here, and pull the exact fasteners and spacing from your jurisdiction's adopted edition before you build.
Why decks fail, and why the ledger is the whole game
When a deck collapses, it almost always fails at the ledger, the board bolted to the house that carries the inboard end of the joists. If that connection lets go, the deck peels away from the building all at once, usually when it is loaded with people. It is one of the deadliest failure modes in residential construction, and it is almost always caused by a bad ledger connection.
That is why the deck section of the residential code, and the inspectors who enforce it, focus so hard on how the ledger is attached and how it sheds water. Get the ledger right and the deck is fundamentally sound. Get it wrong and nothing else you did matters.
The rule that does not change: no nails alone
Here is the one method rule you can carry job to job, because it has been in the residential code for a long time and across editions: a ledger cannot be attached to the house with nails as the sole connection. It has to be positively anchored with through-bolts or lag screws sized and spaced for the load.
Nails pull out. A deck full of people puts a steady, heavy pull on that connection, and nails are simply not made to resist it over time. So the code requires real mechanical fasteners, bolts or lags, driven into solid structure, in a defined pattern. The concept is stable. The exact fastener, the exact spacing, and the exact edge distances are edition-specific numbers, so get those from your adopted edition.
What a correct ledger connection involves
Beyond "bolts, not nails," a compliant ledger connection is about hitting solid structure, laying the fasteners out right, and keeping water out:
- Into solid structure. The fasteners have to land in the house's band joist or other solid framing, not just sheathing or brick veneer. If there is no suitable structure to bolt to, or the house is a type that cannot take a ledger, the deck may have to be free-standing or engineered.
- The right fastener pattern. The code specifies how the bolts or lags are staggered, top and bottom rows, and how far they sit from the edges and ends of the ledger, so the connection is strong and the board does not split. The residential code effectively points to a widely used prescriptive companion, the American Wood Council's DCA 6 deck guide, for this layout. Follow your adopted code and that referenced layout; the exact stagger and edge distances are numbers to confirm.
- Flashing. Water getting behind a ledger rots the band joist it is bolted to, and a rotted band joist is a ledger failure waiting to happen. Proper flashing over and behind the ledger is part of doing the connection right, not an optional finishing touch.
Lateral load, guards, and the rest of the deck
The ledger is the headline, but two more things fail inspections and decks:
- Lateral-load connection. Beyond holding the deck up, the code addresses keeping the deck from pulling away horizontally, often with dedicated hardware tying the deck framing back into the house framing. Whether and how this applies comes from your adopted edition.
- Guards on the deck. Once a deck's walking surface is high enough above grade, it needs a guard, the same fall-protection rule as any elevated walking surface, with a required height and child-safe infill. Do not notch the guard posts in a way that weakens them, and connect rails so they resist real force. The guard trigger height, guard height, and infill limits are covered in the stair and guardrail guide and come from your adopted edition.
Decks also have a design live load they must carry, which drives joist, beam, and footing sizing through the prescriptive tables, or an engineered design when the deck is outside those tables. The load figure and the span tables are edition-specific, so route them.
The engineered alternative
Everything above is the prescriptive path, the tables and standard details for a typical wood deck. When a deck is unusual, tall, cantilevered, oddly shaped, on difficult ground, or attaching to a house that cannot take a standard ledger, it moves to an engineered design signed by a licensed engineer. As with any element, once you go engineered for the deck's structure, you build to that design, not a mix of the design and the prescriptive tables. If your deck is outside the standard tables, ask your building department whether it needs an engineer.
The move
Build every ledger as a positive bolted connection into solid structure, flashed to keep water out, never nails alone, and treat that connection as the most important thing on the deck. Then pull the exact fasteners, spacing, edge distances, lateral-load hardware, load figures, and guard dimensions from your jurisdiction's adopted edition through the Permit and Code Lookup tool, and confirm with your building department. A deck ledger is a life-safety connection, so build it to your adopted edition and let the inspector verify it before you deck over it.
Common questions
Can I attach a deck ledger with nails or screws?
No. A deck ledger cannot be attached with nails as the sole connection, and ordinary screws are not a substitute, it has to be positively anchored with through-bolts or lag screws sized and spaced for the load. This is one of the most stable rules in the residential code and the reason is blunt: nails pull out, and a nailed ledger is how decks collapse under a crowd. The exact bolt or lag size, spacing, and edge distances come from your jurisdiction's adopted code edition, so confirm those with your building department, but the no-nails-alone rule is universal.
Why do decks collapse?
Almost always at the ledger, the board bolted to the house, when that connection was not properly made, usually because it was nailed instead of bolted, or the band joist behind it rotted from missing flashing. When the ledger lets go, the whole deck pulls away from the house at once, typically under a load of people. That is why the code is strict about positive bolted attachment into solid structure and about flashing. Get the ledger connection right and the deck is fundamentally sound; the exact fasteners and spacing come from your adopted edition.
Do I need flashing behind a deck ledger?
Yes. Flashing over and behind the ledger keeps water from getting behind it and rotting the band joist it is bolted to, and a rotted band joist is a ledger failure waiting to happen. Flashing is part of a correct, code-compliant ledger connection, not an optional finishing detail. The bolts hold the deck today; the flashing is what keeps the connection sound for years. Follow your adopted code's requirements and the referenced deck-construction guidance for the flashing details, and confirm anything you are unsure of with your building department.
When does a deck need to be engineered instead of built to the tables?
When it falls outside the standard prescriptive deck tables, a tall or cantilevered deck, an unusual shape, difficult soil, or attachment to a house that cannot take a standard ledger. At that point it needs a design signed by a licensed engineer rather than a prescriptive detail, and once you go engineered for the structure you build to that design, not a mix. Typical wood decks are covered by the prescriptive path and its referenced deck guide. If you are unsure whether your deck is inside the tables, ask your building department before you build.
The honest bit
- No fastener size, bolt or lag spacing, edge distance, stagger geometry, lateral-load hardware spec, deck load figure, or guard dimension appears here on purpose. Every one depends on the code edition your jurisdiction adopted and any local amendments. Get all of them from the Permit and Code Lookup tool and your building department.
- The no-nails-alone rule, the need for positive bolted attachment into solid structure, and flashing are stable across editions, and that is what this guide gives you. The numbers are not stable, so route them.
- This is general guidance on how a ledger connection has to work, not code or engineering interpretation. A deck ledger is a life-safety connection, so build it to your jurisdiction's adopted edition, use an engineer where the deck is outside the tables, and let the inspector confirm it.
Know someone who needs this?
Keep reading
Templates you might need
Was this guide useful?
Didn't find what you were looking for?
Spotted something wrong or out of date? Email us at hello@kilnguides.co.uk.
In crisis? 988 Suicide & Crisis Lifeline 988 ·