A. Christopher DeBlois, a structural engineer with Palmer Engineering in Tucker, Ga., responds: You're right. Lag bolts don't get the same purchase in a 1 1/4-inch-thick engineered LSL (laminated strand lumber) rim joist as they do in 1 1/2-inch-thick framing lumber. If a lag bolt is properly installed, with its tip well through the rim joist and only the threads engaged in the band, its capacity relative to pull-out forces depends on the thickness of the band and the density of the wood. Because LSL rim joists are typically built up of the same wood species used for framing material (and thus have the same approximate density), the big variable is the thickness. A 1 1/4-inch-thick LSL is five-sixths as thick as 1 1/2-inch-thick 2-by stock, and thus has 16 percent less holding capacity. To provide the same total pull-out strength, you'd need to provide six-fifths the number of bolts, an increase of 20 percent.
Although there may be other variables, the end result for shear and pull-out strength to carry the weight of a deck or porch will be similar — 20 percent more bolts in a 16 percent thinner band will provide about the same capacity. (See "Load-Tested Deck Ledger Connections" [3/04] for bolting schedules for 2-by ledgers.)
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