They should have a washer or a large head. You will usually need to pre-drill a 5/16' pilot hole into the rim joist if you are using ½' lag bolts. Your bolts or screws should be long enough to extend at least ½' past the board you are attaching to. 8.5.2012 - Lag Screws. Traditionally, lag screws have been the most common method of attaching decks to buildings. To properly attach a deck ledger using 1/2' lag screws, 5/16' holes need to be pre-drilled through the ledger and rim joist. After that, a 1/2' hole should be drilled through the ledger only. What size lag screws will you need? It all depends on your unique circumstances, but typically ½-inch diameter lag screws will get the job done. First, pre-drill 5/16-inch holes through both the rim joist and ledger, then drill a ½-inch hole through the ledger alone. Guide to Choosing Deck nails, bolts, screes: Porch & Deck Construction . It is also important that at least half the length of the lag is threaded into solid wood. Is it best to use carriage bolts 2 each way or frame around post on 4 . The key is to not over notch or not notch at all depending on the size . To build decks using lag screws, first you have to plan out your deck. Figure out where you want it and what the dimensions will be. Measure out the length, . 12.12.2010 - Rule-of-thumb deck ledger fastening is out and the code is in. . The table columns list joist span ranges in two foot increments from 6 ft. to 18 ft.; the . Lag screw tips must penetrate the house rim joist – that's at least ½ in. 25.12.2017 - Before the 2009 IRC, builders usually staggered lag bolts high and low . the joist to the lower bolt; the numbers depend on the size of the joist:.