The generic name is LVL (laminated veneer lumber). Other companies provide similar products, such as Boise Cascade's VersaLam and Georgia-Pacific's GP Lam LVL®. Laminated structural lumber is used both for beams and joists, among other uses.
Much like plywood, thin sheets of wood are sandwiched and bound with super-strong glue. Unlike plywood, Microllam and other LVLs are solid, heavy, and intended to carry loads.
Beams, Joists in Older HomesIf you have an old house and you're lucky enough to be able to get in the crawlspace or basement, you'll have a good peek at the joists and carrying beams. Unless the home has been renovated recently, no doubt you will be viewing sizable joists: two-by-eights or two-by-tens. Carrying beams, as the name infers, carry huge loads and are serious hunks of timber. In the past, size equated with strength.
But with newer advancements in lumber processing, manufacturers were able to produce lighter and smaller lumber with the same or even greater strength.
Cost, Where to Use Microllam and Other LVL LumberUse Microllam and LVL for rim boards, carrying beams, and headers. Microllam is also used to carry long flooring spans in the form of I-beam joists. Very wide windows and doorways will almost always use some type of special laminated veneer lumber. The wide spans of garage doors benefit from Microllam construction, as well.
Microllam and most other LVL runs very high per linear foot, and costs vary according to width and depth of the material. To give you an idea, expect to pay $35-$50 per foot for 6" x 18" Glulam. One supplier, Albert Tamm, has quoted $8.85 per linear foot for 1 3/4" x 16" LVL and $4.62 for 1 3/4" x 9 1/2" LVL, not including taxes and shipping.
Tip: If you've got saggy, mushy joists, consider sistering your existing joists.