Structural composite lumber: LVL, PSL or LSL?   Modern builders also can buy laminated-veneer lumber (LVL), parallel-strand lumber (PSL) and laminated-strand lumber (LSL), all of which are interchangeable for some applications.  If you find this alphabet soup confusing, take heart.  Although all three types of structural composite lumber (photo below ) share some similarities (they are strong, predictable and more expensive than solid lumber), they do each have distinct traits that make it easy to choose among them.

Like plywood, LVL is a glue-laminated sandwich of thin wood veneers peeled from logs.  But where plywood orients the grain of adjacent plies at right angles, LVL orients all wood fibers parallel to the long axis of the stock for maximum strength.  The laminating process converts small young trees into structural lumber that's much stronger than #2 Douglas fir while nullifying the defects and size limitations of solid lumber.   Like LVL, PSL begins as a pile of veneer.  But PSL veneer comes from lower-grade trees peppered with defects.  Defects are dispersed by slicing the veneer into strands up to 8 ft.  in length, then bonding the strands lengthwise into rectangular billets that are milled into finished stock.  Because veneer supplies are limited, LSL dispenses with the veneer.  It's made by cutting low-grade trees into irregular strands up to 12 in.  long and bonding them into billets that are milled into finished stock.

LVL, PSL and LSL come in a variety of sizes, some of which overlap.  LVL commonly measures 1-3/4 in.  thick, 3-1/2 in.  to 18 3/4 in.  deep and up to 60 ft.  long, though thinner and thicker stock can be ordered from some companies.  It's normally used for beams, headers, hip and valley rafters, scaffold planks, wood I-joist flanges and rim board for wood I-joist closure.

PSL is used for posts, beams and headers.  Beams and headers are 1-3/4 in.  to 7 in.  thick, 9-1/4 in.  to 18 in.  deep and up to 60 ft.  long.  Posts range from 3-1/2 in.  sq.  to 7 in.  sq.
LSL is used for posts, beams, headers, studs and rim board.It's also used for roof trusses, as core stock for windows and doors, and as flange stock for wood I-joists.  The posts, headers and beams are 3-1/2 in.  thick, 3-1/2 in.  to 16 in. deep and up to 48 ft.  long.  The studs are 1-1/2 in.  thick, and the rim board is 7/8 in.  to 1-1/2 in.  thick.
 Other factors also come into play.  To eliminate the need for a crane, some builders routinely fabricate big beams in place by sistering 1-3/4-in. thick LVL or PSL sections (whichever type is stocked locally).  PSL and LSL resist moisture-induced warpage better than LVL, which can make them the best choice where beams will be exposed to wet weather during construction.