Engineered Lumber

One of the inevitable consequences of our legal system is a reluctance to adopt technologies and building systems that are perceived as “new”. Most of the new technologies being deployed today are perceived as new not because they are, but because it has taken decades for them to begin to be accepted by builders.

Ten years ago, for example, less that 30% of homes used engineer lumber in their flooring systems. As of 2004, almost 50% have I-joists installed rather then sawn timber girders. GluLam beams have also been around for over a decade, yet they’re still typically deployed only in special situations that require support over a long span.

That said, the use of engineered lumber is becoming more common. The quality of sawn lumber continues to fall, causing more and more problems for builders. Changing building systems completely requires a learning curve and level of risk that make most builders uncomfortable. So in the hunt for alternatives that use construction methods with which they are familiar, more and more contractors are turning to engineered alternatives. As contractor John Spier put it in Building with Engineered Lumber, “Today I use engineered beams, roofs, walls, and headers as well. My wife and partner maintains that most customers are oblivious to anything but the bottom line, but we leave the jobs knowing that they got a better result.”

To say the least!

Types of Engineered Lumber

By now, I-joists and GluLam beams are engineered products that most customers are familiar with. But when it comes to the array of engineered wood products that your designer, architect, or contractor can bring to bear on your project,it’s less than half the picture — and shrinking.

LVL stands for “laminated veneer lumber”.

A GluLam beam is LVL. But LVL dimensional framing lumber is also available. Like the beams, LVL framing material is much stronger than its sawn counter part. One builder observed that when a framing plan for a three story apartment building called for 3×4 frames on the first floor, he got approval to use LVL 2x4s instead because of their superior strength. By doing so he felt he had saved the developer considerable money, and had provided a superior product.

And in many ways it’s true. Sawn lumber has many drawbacks that many people don’t really think about:

First, unless a special order is placed for air dried lumber (which costs significantly more), virtually all framing material is “kiln dried”. Which means it’s usually so wet it “weeps” with sap when a nail is driven into it. As it dries, it shrinks. As virtually every frame in the building shrinks, the shape of the building changes, with predictable results. Doors no longer close properly. Dry wall cracks. Walls pull away from tiles or showers or cabinets. Corners are no longer square.

Second, as the quality of framing lumber continues to fall, problems with rot and termite damage climb proportionally. It’s now not uncommon to have a significant rot problem in a twenty year old home. That was unheard of as little as thirty years ago!

Third, as the quality of framing lumber continues to fall, the number of “culls” (rejects) increase, and the number of actually straight pieces falls. This increases many of the problems identified above.

The use of engineered lumber addresses all of these problems.

LSL stands for “laminated strand lumber”.

In an engineered wood structure LVL is the common choice for bearing walls and LSL for the interior walls. In a non-engineered wood structure LSL is often used on walls that the contractor wants to make sure are perfectly straight: Kitchen walls on which cabinets will be hung, and bathroom walls that will be tiled, for instance.

LSL has the interesting characteristic of being so sharp edged that you can cut yourself on the corners! It also has the obnoxious habit of absorbing moisture right out of the air. When it arrives on a job site, LSL has a moisture content of only 5%. If left unwrapped and not installed, LSL can actually swell and warp as it sits on the ground. Therefore, a delivery schedule is usually worked out with the supplier so that only the quantity of lumber than can be framed each day is delivered to the job site.

I-Joists are becoming the favorite of many contractors for girders and floor joists.

They’re lighter, they use considerably less wood for the strength and span they can cover, and they come in configurations that make the job of plumbing and wiring beneath the building easier.

MDF stands for “medium density fiberboard”, which lead many people to think immediately of “flake board”.

But the two are not the same. MDF comes in thicknesses not available in any other product. It also comes in many “flavors” (though some are hard to come by in some areas). Unlike flake board, MDF is (or can be) sufficiently water resistant for use in cabinets. (Yes, I know that flake board is used in cabinets too, and if you know that, you’ve probably seen the icky long term result).

Other types of engineered lumber are Oriented Strand Board (OSB), which is now so common it’s hardly worth mentioning, and finger-jointed lumber. Finger-jointed lumber is made by gluing short pieces of wood that would normally be scrap into usable lengths. It’s useful in non-critical, non-load bearing interior walls.

Cost

Not surprisingly, when compared linear foot to linear foot, engineered lumber costs more than sawn lumber. But, as the Sustainable Building Sourcebook observes: “When labor savings and reduced job site waste are considered, the cost is highly competitive.” In fact, it’s pretty much equal. And finger-jointed lumber is equal to the cost of sawn lumber, even on a per foot basis.

Is it Really Green?

Opinions vary. For certain, the resins used to make engineered lumber typically don’t use formaldehyde binders, but that doesn’t mean they don’t give off VOCs (though it does produces less VOCs), and it also doesn’t mean those binders are made from environmentally friendly compounds.

BuildingGreen.com put it this way: “While not free from ecological concerns, engineered lumber products can provide a significant environmental advantage over solid wood by efficiently utilizing fast-growing, small-diameter trees.” In other words, engineered lumber is (usually) produced from “farmed” trees.

In the end, there are probably better alternatives than engineered lumber if you’re open to more modern building methods than studs and joists. But if you want a stud built home, or if you need to use some framing in your ICF or SIP built home, engineered lumber is a much better alternative than sawn lumber all the way around.

Technorati Tags: engineered lumber, sustainable building, LVL, LSL, GluLam, MDF, building green, studs, lumber

This entry was posted on Sunday, August 26th, 2007 at 7:15 pm and is filed under Building Systems & Methods. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.