Ledger board

The ledger board for a deck is the piece of lumber that’s attached directly to the house.  All of the deck joists then are attached to this ledger board, so the ledger board carries a lot of load and it needs to be attached very securely.

When decks fail it’s usually because the ledger board pulls away from the house and the deck collapses.  An online search for “deck collapse” will quickly yield dozens of pictures of decks that have pulled away from the house because the ledger board failed.

Decks can be a great do-it-yourself project, but properly attaching the ledge board to the house isn’t always within the realm of expertise for the typical homeowner.  Here are some of the basic rules for attaching a ledger board to the house.

First, nails alone are never sufficient for attaching a ledger board.  This is pretty much rule number 1 in deck building school.  Sometimes a deck builder will nail the ledger board in place quickly, just as a way to hold it in place while the final bolts are installed.  But nails alone are never sufficient.  Nails don’t have enough pull out strength – it’s far too easy for the ledger board to just pull away from the house and pull the nails out with it.

Also, you aren’t allowed to attach a ledger board to brick veneer.  It’s possible to have fasteners go through a brick veneer wall and attach to the structure behind, but it’s extremely difficult to do that and it really isn’t a practical solution.  So, no ledger boards on a brick veneer wall.  If you want to install a deck next to a brick veneer wall then the deck should be free standing – not supported on or by the house structure at all.

You also aren’t allowed to attach a ledger board to any type of overhang.  The ledger board needs to be attached through the sheathing and onto the rim joist, which sits directly on top of the foundation.

The ledger board is generally a piece of 2×10 or 2×12 lumber (although a 2×8 is allowed in some situations), pressure treated or naturally durable, No. 2 grade or better.  The ledger board should be attached directly against the house, not through any siding.  The only thing between the ledger and the house sheathing should be the house wrap (Tyvek) or felt paper.  The ledger should be attached directly to the rim joist, through the sheathing.

As a quick refresher, on top of the foundation wall goes the sill plate laid flat, and the rim joist sits on top of that sill plate at the outer edge.  The floor joists then sit on the sill plate, butted up against the rim joist.  Then the sheathing (plywood today, but 1×6 boards in days of yore) goes over all that and just a short way down over the foundation.

The ledger board should be attached with standard ½ inch lag screws or through bolts with a nut.  They should be hot dipped galvanized or stainless steel.  Very commonly used today are ¼ inch structural lag screws, although no code or standard I’ve ever seen actually allows them.  The fasteners must solidly anchor the ledger to the rim joist, and lag screws must go all the way through the rim joist and the screw tip must stick out a little bit.  If you’re trying to do this yourself, and you aren’t sure what you’re fastening to, then stop.  Have an experienced deck builder do this for you.  Fastening into anything other than the rim joist is a recipe for disaster.  In some cases you’ll need to remove some of the finished wall or ceiling in the house to be able to get a look at the structure.  That’s part of the fun of building a deck.

These days many rim joists aren’t standard 2x lumber, but instead are some type of engineered lumber.  If this is the case then you need to follow that lumber manufacturer’s instructions for attaching a ledger board.

The ledger fasteners should be spaced according to some very specific guidelines, as shown in the diagram below.  They should be staggered in two rows.  A single row isn’t as strong, and it also tends to create a weakness in the ledger board along the line joining all the fasteners.  The rows should be a maximum of 5 inches apart.  The fasteners should be no closer than 2 inches to the top and side edges and no closer than 0.75 inch to the bottom edge.  The minimum distance from the top edge to the bottom row of fasteners varies according to the size of the ledger board.

Of course this doesn’t include perhaps the most important issue with the fasteners, and that is the horizontal spacing between them.  That required spacing varies tremendously depending on the size of the deck (how far out from the house the joists span), what the required load capacity is for the deck (which depends on things like snow load in your area), what type of fasteners you’re using, and even how thick the house’s wall sheathing is.  The spacing in some cases can be as large as 36 inches for a small deck with no anticipated snow load, down to as small as 7 inches.

The numbers are found in the International Residential Code 2021 table 507.9.1.3(1).  I’m not going to reproduce that table here.

The ledger board helps carry vertical loads from gravity acting on the deck and the things on it.  But we also need to deal with lateral loads.  It’s these loads after all that tend to pull the ledger board off and away from the house.  It really doesn’t make much sense to prohibit just nailing the ledger board to the house, but once it is bolted then just allowing the joist hangers to be nailed to the ledger.

So a few code cycles ago a requirement was added for lateral load resistance.  Here’s a good cutaway view of one very typical solution.  There is a bracket installed on one of the deck joists within 24 inches of the outer edge of the ledger, and a similar bracket installed inside on a corresponding floor joist.  A threaded rod runs between the two brackets and connects the deck to the house.  There should be two of these devices, one at each end of the ledger board.

There are other ways to provide this lateral load resistance.  A simple bracket can be installed at the bottom of the deck joist and then attached to the foundation wall or some other structural part of the house.  You should see at least four of these devices on a standard deck.

Lateral load resistance is much more important on a tall deck than a short one.  Partly because a failure of a tall deck leaves occupants with a longer drop, but mostly because a tall deck can produce much larger lateral loads owing to the large moment arm effect of the taller posts.

This is one of my longest blog posts, and I’m just discussing a simple piece of wood attached to your house.  But this simple piece of wood carries a lot of load and when installed wrong it’s responsible for the vast majority of structural failures in American houses.  Please be safe.