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Q.Why are LVLs sized differently than framing lumber? I can understand the 1 3/4-inch-thickness dimension, because two laminations make up a matching header for a 2x4 wall, but why are they 9 1/2 inches deep instead of 9 1/4?

A.Paul Fisette responds: First of all, LVL is also sold in depths of 7 1/4, 9 1/4, and 11 1/4 inches to match standard stick-framing sizes. Take a look at the LP Gang-Lam site ( www.louisianapacific.com/products/) or the Trus Joist Microllam site (www.trusjoist.com/EngSite/), for example. However, LVL is also available in nonstandard sizes like 9 1/2 and 11 7/8 inches all the way up to 24 inches deep. You will find that the deeper 9 1/2-inch and 11 7/8-inch versions carry a little more load than the 9 1/4-inch and 11 1/4-inch stock, but that's not why distributors push nonstandard depths. It's actually because the manufacturers don't want you to mix engineered wood with sawn lumber. Look at the product literature for I-joists, which are made by the same companies that sell LVL. You will see that they sell 9 1/2-inch and 11 7/8-inch I-joists as well, not 9 1/4- or 11 1/4-inch.

Swelling, shrinkage, and stability characteristics of engineered lumber are much different than those of sawn lumber, so mixing is discouraged. That's why there's been a trend toward engineered wood floor systems, which use a combination of LVLs and I-joists but no dimension lumber. Nevertheless, manufacturers realize that builders will have projects where matching sawn lumber is required, especially in remodeling, so they also offer "standard" sizes.

Paul Fisette is director of Building Materials and Wood Technology at the University of Massachusetts at Amherst and a JLC contributing editor.