While new provisions in the 2009 International Residential Code should lead to better deck construction, there have been misunderstandings about some of them. Experts say that one in particular will likely bring unintended consequences.
One of the code writers' priorities was to prevent catastrophic deck collapse, which led them to focus on structural loads at the ledger board. For instance, attaching a ledger to a cantilevered bay window has always been bad practice but wasn't specifically prohibited. That changed with the new code, which insists that such a ledger be supported by joist hangers attached to double 2x girders on either side of the bay. And the ends of those girders can no longer rely on the joist hangers for support: Now they must bear either on the home's mudsill or on a structural post.
There is also a new bolting schedule. Where the previous code included a vague requirement about ledger fastening that would account for all loads, the table now tells the builder how many lags or bolts must be installed, and where, for different joist spans.
These changes codify things that good builders have been doing all along. "They're common-sense items that actually make life easier for the builder," says Mike Guertin, an East Greenwich, R.I., builder who also teaches seminars on deck construction. "In the past, we had to rely on performance criteria that were open to interpretation. Now we have clearer guidance on how to satisfy the code."