Deck Ledger Bolting by the Code
The 2009 IRC gives us a prescriptive bolting and lag screwing schedule to follow when mounting a deck ledger to a house. Table R502.2.2.1 has three options: ½ in. bolt, ½ in. lag screw and ½ in. bolt with the ledger spaced off the wall sheathing by ½ in. for those who like the flow-through design. (see photo)
The table columns list joist span ranges in two foot increments from 6 ft. to 18 ft.; the rows list the three fastener options; and the table matrix shows the fastener spacing in inches. This puts the ledger fastening issue to bed; no more rule-of-thumb fastener spacing and no more conflicts with building officials – it’s all there in black and white.
Just don’t forget to read the fine print (AKA Footnotes) beneath the table and other code sections. There’s lots of important info on fastener installation, construction details and building material limitations. (see photo)
- The bolts and lags must be hot dipped galvanized or stainless steel.
- Lag screw tips must penetrate the house rim joist – that’s at least ½ in.
- Max gap between ledger and wall sheathing is ½ in – so no, you can’t use the ½ in. bolt with spacer option over the siding unless it’s T 1-11.
- Bolts and screws must be located 2 in. down from top and up from bottom of ledger and staggered up-down. Plus you need to double fasteners at ledger butts and ends.
- House rim joist must be minimum of 2x sawn lumber or 1 in. x 9 ½ in. Douglas Fir LVL – no attachment is allowed to strand lumber, SYP LVL, the mudsill, I-joists, floor trusses or other materials. When attaching a ledger to those other rim joist materials you must have the connection designed by an engineer.
- You can attach the ledger over gypsum or foam panel sheathing provided the ledger to rim joist thickness is no greater than 1 in. in total.
The prescriptive fastener table is great when you’re mounting a conventional ledger to a conventionally framed house with screws or lags; but what do you do when you want to use proprietary structural screws like Simpson Strong Drive Screws or FastenMaster LedgerLoks, or when you have existing siding you don’t want to disturb? There are solutions and I’ll address them in future postings.
Footnotes to Table R502.2.2.1