What is engineered lumber and should I use it in my addition?

The short answer is yes if you can afford it. Here’s the long answer.

Engineered lumber are structural wood products that have been “engineered” or designed to be stronger, straighter, and more uniform in size as compared to their conventional lumber cousins. Conventional, or dimensional lumber, are pieces of wood cut out of certain species of trees and come in different standardized sizes. The trees most commonly used are Douglas Fir, Larch, and Spruce.

Just about everybody has heard of a 2 by 4 which is actually a piece of wood 2 inches thick by 4 inches wide. Well, sort of. The term 2×4 is what is known as the lumbers nominal dimension. Many many years ago when they first started manufacturing lumber it probably was either a true 2 inches thick and 4 inches wide or close to it. But over time the actual size shrank in order to get more pieces out of the same tree. Today a 2″x4″ actually measures 1 1/2″ x 3 1/2″. The 1 1/2″ thickness has become an industry standard and applies to other sizes as well. For example, a 2″ x 10″ is 1 1/2″ thick by approximately 9 1/2″ wide. Some are 9 1/4″, some are 9 5/8″ etc. The thickness remains the same but the width can vary due to the way that wood expands due to the moisture content that it contains. This can be an issue when you are lining up a bunch of 2″x10″ for floor beams, or joists, and the varying heights cause a slight rippling effect in the subfloor. The other issues with dimensional lumber are the fact that no two pieces are alike in terms of strength and there is a limitation as to how long the lumber can be. Usually, 24 feet is the maximum length for dimensional lumber.

But for many many years this was the only thing, other than steel, that was available to build our houses. While it did a great job overall, new technology arose that allowed manufacturers to develop a product that was made from wood but solved many of the limitations of conventional lumber. Since engineers were needed to design this product in order to be sure it had the requisite strength, they called it “Engineered Lumber”. A new industry was born.

Without going into all of the boring mathematical details of why and how this product works, let’s just use a simple example. Let’s say you were building a small bridge and you had only one piece of wood to use. The distance from one side to the other was 10 feet and you had a piece of 2″ x 12″, which was 14 feet long. Obviously the piece is long enough to span the distance with 2 feet resting on one side and another 2 feet on the opposite side.

The question is which way would you install it to achieve the greatest weight-bearing capacity. You might be tempted to lay it flat with the wide face touching the ground. This would create a wider surface to walk on but it would be very bouncy when you got in the middle of the span. Turning it on edge so that the 1 1/2″ side was touching the ground would make your bridge much stronger, albeit difficult to walk on. But the principle is what is important here.

So imagine if you took many pieces of wood that were oriented in this fashion and put them together so that they were one piece. Now you would have something that is extremely strong. That is what the engineers did. They came up with a special glue that would last a very very long time and resist water. Then they sliced pieces of wood called veneers in such a way that the grain pattern was perpendicular to the direction of the load and glued many of them together. They called this Laminated Veneer Lumber or LVL. Because of the machining process, LVL’s are very uniform in terms of height because they are not subject to humidity changes as is conventional lumber. The glue is highly resistant to absorbing water as well. Lengths beyond 24 feet are possible due to the fact that they can glue up the pieces in on offset patchwork fashion. Theoretically, they could make an LVL of infinite length if they wanted to, but for practical purposes, they usually max out at 60 feet. Here is what one looks like. Notice the multiple plies it has.

The main purpose of an LVL is to replace the solid sawn wood beams of years ago. They are much stronger than an equivalent sized sawn beam and have the other advantages of uniform height and longer lengths. They are great for girders and headers, which are special-purpose beams designed to carry a lot of weight. However, one of the disadvantages of an LVL is it costs more than its solid sawn cousin.

But for beams, it is definitely worth it because of the advantages and because there are usually not that many beams in a typical house. At least not nearly as many as floor or ceiling joists or rafters. These are the multiple pieces that are usually spaced 16″ or 24″ apart and form the skeleton of the house. Using LVL for this many pieces would be cost-prohibitive in most cases. So a different kind of engineered lumber called an I-Joist, was devised. It is designed upon the same principle as a steel I beam, with a top and bottom flange separated by a thin “web” of wood in the middle. Here, in the middle of the photo, is an example:

Because the center web is thin, the overall weight and cost to manufacture is lower than an LVL. But don’t be fooled into thinking it’s not strong. The top and bottom flanges do most of the work. When a load is placed on the I-Joist, the top flange is under compression as it is forced to bend and the lower one is under tension or stretching forces. Wood is an excellent material to resist both of these forces and as such that wood joist is very strong. It also has properties that are similar to the LVL, uniform height, and greater lengths. Its also easier to drill through the thinner web to run electrical wires and plumbing, but you must know where and how big of a hole that is allowed. There are special charts that illustrate this. Placing a hole too big or in the wrong place can seriously compromise the strength of the I joist so make sure that it doesn’t happen on your job. Some joists come with pre-drilled knockouts that require just a couple of hits with a hammer to remove. I joists will make your floor stronger as well as much more resistant to the squeaks caused by an uneven subfloor found in conventional lumber. Hope that helps and Good Luck!

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