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Ledger Board (1)

A ledger board is used to connect the deck to the house. If attached properly, it provides a great deal of strength and stability to the deck, and forms a trouble-free leak-proof connection to the house. Installing a ledger board properly means making sure to use enough bolts to carry the deck weight and to correctly install metal flashing to prevent water infiltration. It's important to make sure to get the ledger securely fastened for safety reasons and the flashing done well to prevent water damage. When it comes to the ledger board, getting it right the first time is especially important since trying to go back and make repairs after the fact is virtually impossible.

When attaching a ledger board to the side of a wood framed house, the ledger board is either through-bolted or lag-bolted onto the house's band joist. Of course, there are special situations. Sometimes the floor in the house is sunken or made out of engineered I-beams. Other times, the house is stucco, has a brick veneer, or may be concrete where the ledger board needs to go. All of these special situations are covered in the ledger board section. For now, we'll briefly look at the most common case involving bolting a ledger board to the band joist of a wood framed house.

To begin, it's important to look and see how the well the house's band joist is nailed on to the house. Typically, there are only a few toe-nails into the sill plate below. These nails combined with the nails driven into the ends of the floor joists are all that holds on the band joist. Unfortunately, toe-nailing and nailing into end grain are the two weakest ways to nail together wood. This is important to realize since if the house's band joist isn't firmly attached, forces on the deck could cause the band joist itself to be pulled right off.

If you're familiar with construction practices, you may be thinking that the 1/2" thick underlayment of plywood or OSB (flake board) on your house will help hold on the band joist. Unfortunately, most framing crews like to sheet the walls while they're laying down. They then stand up the walls and nail them in place. Later, they come back and cover over the band joist with a separate strip of underlayment. In other words, there is a break in the underlayment at the joint between the walls and the band joist. As such, the underlayment doesn't help hold on the house's band joist.

There are several ways to strengthen the band joist's connection to the house. I'll mention one here and you can read more about it in the ledger board section. Pre-drill and use 4" toe-screwed deck screws every 12". Drive them up into the wall plate above and down into the sill plate below. Even though toe-nailing isn't particularly strong, if you pre-drill so the band joist doesn't split and properly angle the screws, this method will work fine.

Now that the band joist is firmly connected, we can bolt on the ledger. As noted, there are two basic methods to do this. The first is to use bolts that go all the way through the house's band joist and are secured with washers and a nut. The second is to use lag bolts. Either method is fine as long as you follow the ledger tables for the number and spacing of the bolts.

For example, if we through-bolt the ledger board onto the band joist alone and we're building for a 60 pounds per square foot (psf) drifting snow loaded deck, the tables say we'll need to use three 1/2" bolts every 13 inches when the deck joist are 12 feet long. Now this may seem like a lot, but a 60psf drifting snow load really gets heavy right next to the house. By the way, if you haven't already read this, most codes in areas that get snow require designing for sliding and drifting snow that tends to pile up next to the house in a wedge shape.

If that number of bolts sounds like too much work, or you don't want to hassle with a bolt spacing that will interfere with your deck joist spacing, there are other options. For example, you could add a solid block behind the house's band joist. Without going into the details here, this added thickness increases the bolt capacity. The result is that we'll only need to use two 1/2" bolts every 14" for the same 12 foot long deck joists.

If it's not possible to get behind the house's band joist to tighten nuts or add blocking, lag bolts can be used. According to the National Design Specifications (NDS), lag bolts must have a minimum of four times their diameter (4D) thread engagement to be used at all and a minimum of (8D) to achieve their rated strength. What this means is that 1/2" bolts must thread into wood at least 2" thick to have any holding power at all. To achieve their full strength, they need to be threaded into wood at least 4" thick.

The thickness of a house's band joist is only 1.5". That's not enough for 1/2" or larger lag bolts. If you're going to use larger lag bolts, you must locate the house's floor joist and drive the lag bolts into the ends of them or increase the thickness of the band joist using blocking.

If your house has vinyl siding, uses hollow concrete block, or anything in-between, BestDeckSite can show you how to securely attach the ledger board and seal it against water infiltration. We pride ourselves on providing complete, detailed and thorough information. To subscribe, see our Get A Password page.