Also included in this section on a decks design is help with figuring out the size and number of bolts needed to attach the ledger board and sound advice on how to keep water out. To my dismay, I've actually seen several books on a decks design recommend countersinking the ledger board bolts and/or installing a wimpy 2" stick of flashing on top of the ledger. Both of theses are bad practices.

It's very important to have a decks design that gets the critical deck-to-house connection right. To be more specific, if you drill out 1/3 the thickness of the ledger board to countersink the bolt heads, as these books on a decks design recommend, you’ve effectively reduced the load bearing capacity of the bolts by 1/3. Now that’s fine if you’ve made calculations that verify that your decks design can afford to loose that bearing strength. Unfortunately, these books on a desks design never address these concerns.

In this section on a decks design, I’ve developed a table based upon NDS guidelines that tells you exactly how much a 1/2" and 5/8" bolt can carry. This table was specifically created to help you get your decks design right and uses design values for outdoor, treated lumber. To help you along the way, I run through an example showing you how to determine the weight of your deck. Knowing your decks design weight and using the bolt table, you can easily find the correct bolt spacing.

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