Engineered Lumber:
Strong beams that allow for open spaces with no posts

Engineered lumber is made from wood veneers and particles, glues, and resins to create large structural elements that virtually never fail if used correctly. Manufactured in a controlled environment, the load factors for these materials are precisely calculated for every size. Engineered lumber also saves trees by using more of the whole tree—typically 30 percent more than sawn lumber—so fewer need to be cut down.

The two most common engineered wood products used in modern framing are LVL beams and I-joists. Laminated veneer lumber (LVL) is just what it sounds like: wood veneers (typically poplar, pine, or fir) laminated together under heat and pressure with a moisture-resistant resin.

Because the grains all run in the same direction, LVLs are extremely stiff and stable. They come in thicknesses up to 3 1/2 inches, depths from 3 1/2 to 24 inches, and lengths as much as 60 feet.

Because of their tensile strength—meaning they can hold up a lot of weight along their length without sagging—LVLs make great door and window headers, stair stringers, ridge beams, cantilevered roof supports, and other carrying beams. And as they have the ability to span long, open spaces, LVLs can eliminate the need for posts in basements and garages.

I-joists are engineered beams made in an I shape. They are made up of a vertical web of dense oriented strand board (OSB) in the middle, with a horizontal flange of dimensional lumber or LVL above and below. They're used for joists and rafters, because they're lighter than sawn lumber and able to span greater distances. And unlike lumber, they can take large holes for plumbing and ductwork without compromising strength. All these factors add up to higher ceilings, because a smaller I-joist will carry the load of a deeper one made from dimensional lumber, and systems don't need to run under the ceilings in added framed channels, or soffits.

The flanges in I-joists are also wide—up to 3 1/2 inches—providing more room to glue and nail subflooring. "Any time you get more fastening surface, your floor will be stronger," says Tom, who makes sure to use stiff I-joists under floors with rigid finish materials like tile or stone.

The benefit of engineered lumber is its stability and strength. But Mike O'Day, manager of engineered lumber for Georgia-Pacific, one of the largest manufacturers of building products, says you can't generalize about the strength of engineered wood versus dimensional lumber—in part because the latter is so varied in quality. "The real advantage," says O'Day, "is not so much that engineered wood is stronger, although in many cases it is, but that it is more consistent and predictable." It's worth noting that engineered lumber is generally more costly than dimensional lumber. And there have been environmental concerns about the phenol formaldehyde binders used in most engineered-wood products, which can off-gas. Though these pieces are usually encapsulated behind wallboard, manufacturers have begun using a greener, formaldehyde-free binder called PMDI in a few products.

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