There has been an incredible amount of research and development put into the strength, design, and manufacturing of trusses. Trusses and groups of trusses have been built and tested to the breaking point so the exact strength of a truss is known. Do all trusses have the same strength? Are trusses all user friendly? The answer is no due to the nature of framing and not all lumber has the same grade, density, and quality. Does it make a difference what grade of lumber is used and how the finished truss looks? Yes!
Trusses are often viewed as dimensional lumber tied together with plates and aren’t much different then stick framing or individual rafters. This couldn’t be farther from the truth! When you buy a truss, you’re not just buying some lumber! Trusses are in the category of engineered wood products. They have been designed to certain specifications based on extensive testing and are built to that end.
The Best Lumber Grade for Wood Trusses
Let’s delve a little deeper into the design of a truss and how well it was manufactured. Lumber quality and grade actually has quite a bit to do with the strength of a truss. If you have a 2×4 truss that is spanning 26’ and it has a 1 inch knots sprinkled along the top and bottom cord along with some wane on the edge and under a connecting plate, how much strength does the truss lose just by having it in there? A truss using #2 for the main cords is just not going to be as good of quality as a truss using a higher graded lumber with fewer knots and wane like a Select Struct grade which has been visually graded for quality.
Another way to look at lumber is by this chart. This chart is only for a reference and shows no actual type of lumber. In fact, bending strength is normally shown as a psi number. This is simply showing the difference in lumber from grade to grade. The higher the relative bending strength is, the more the board can handle in a truss application. You can see for yourself how the numbers change as the grade of lumber changes.
Wane is a defect in dimension lumber that is caused by remaining bark or due to the curvature of the log, a beveled edge. If this beveled edge comes under a plate by a joint on the truss, the teeth of the connector plate is suddenly not getting the amount of bite that it was designed to have. This potentially makes a weak point on the truss depending on the reactions at that joint.
Knots, wane, and splits make a truss weaker for handling as well. Once trusses are built and delivered, they still need to be installed on top of the walls. That requires handling the trusses and the more they get moved, picked up, swung around, and so on, the greater the chance of something breaking becomes. Chords and webs can break much easier when they have large knots or splits in the lumber. When something does break, it takes time to fix it. If the project is one that is being inspected and requires an engineer seal on everything, it will take even longer to get a sealed repair on the truss.
Use Quality Lumber for Webs
Lumber grade also makes a difference on the webs. Even though some people would say that the webs are not as important on the quality or how good they look, there is one thing to keep in mind. The webs in the truss are what give the outside shape of the truss its strength! So does it make sense to put the lowest grade lumber in them? Some of those webs have quite a load on them and if cheap lumber is used, they will require more web bracing to make up the strength they lack.
Did you just catch that phrase “more web bracing”? What framer in the field likes to put on web bracing in the trusses once they are up? None, that I know of. I’ve never seen a framer excited about getting to install web bracing. Usually if the truss requires web bracing, it has been marked with a tag or the engineered drawings will also show if it needs it or not. Some framers see the bracing tag but don’t put bracing on because they feel like it is not important or else it’s too much work.
There is a direct connection between the quality of the lumber and how much web bracing will be required. So if a higher grade of lumber is used and therefore better quality with fewer knots and less wane, there will be fewer webs that require web bracing which saves you time and money. This is especially nice when you are talking about a post frame shop or barn and the trusses are farther apart. This means that the framer is happier because he doesn’t have to put it in and it also saves him a lot of time and work.
Ordering the Best Wood Trusses
Now if you are going to be ordering trusses from a company, how much difference is a better design and better lumber going to make for you when you put the roof up? It will make quite a difference! Another thing we did not even mention about on lumber quality is how straight and true the boards run. What happens if the boards are warped or bowed? One of the first places you will notice it is on decking and sheetrock. If they are curved, bowed, and twisted too much, they will require additional time getting them straightened and spaced right so the decking and sheetrock will come out right and nail on good. But if it there is too much warp and bow, it can affect the sheet rocker and in turn, affect how the room looks once it is completed.
So does it matter how the truss looks when it arrives at the jobsite? If they look good, they probably have good lumber in them. This also means that your structure will be better and last longer. There is less chance of it failing when the wind blows or an extra heavy snow comes. You will also have fewer problems with the structure as it holds up under normal use. And now you know what difference it can make to you. A well-built truss may not be the cheapest truss on the market but it will pay itself back as it fits well and does not require as much constructing time.
Timberlake TrussWorks only builds trusses from the finest lumber. Almost all the lumber used in the shop is Select Struct grade or better. Most of the lumber is Hem-Fir which is very stable, strong, and easy to work with. Only choose the finest lumber when it comes to your trusses.
Timberlake TrussWorks in Oklahoma provides the highest quality trusses from northern Texas, all of Oklahoma, to well over half of Kansas. This area includes towns such as Wichita Falls, Lawton, Oklahoma City, Woodward, Tulsa, Guymon, Liberal, Dodge City, Wichita, Hutchison, Great Bend, and Salina. Give us a call and we’ll be happy to send you a quick and free quote at 580-852-3660!