First, wane occurs often when lumber is manufactured and cut close to the outside of the timber, resulting in missing material or a bark area. This is done to increase the yield of the timber, which increases lumber manufacturer profits but creates some issues for lumber users. Prime grades limit wane severely, which results in a more expensive product for truss manufacturing because the lumber manufacturer is sourcing a much lower yield of nearly perfect lumber. [For all images, See PDF or View in Full Issue.]
Given that cost-and-supply dynamic, can we afford to eliminate wane? The short answer is no. Unless you have clients that can afford the premium lumber, you will be utilizing lumber with wane in your operations.
So, what is the answer to our question posed in the title of this article – what should truss builders do when they have to deal with wane in the plated area? Because we are not going to throw out usable lumber, the answer is that a smart builder will adjust for the wane and, when practical, eliminate the wane by culling the part or piece.
To Adjust or To Cull
Approaching the problem of wane in lumber, the actual decision making can be approached in this order.
First, does wane exist? Yes or No. If No, then the lumber still needs to be checked to identify other potential defects. If Yes, then adjust the connector size to add additional tooth count to the connector plate. But, what if “adjusting” is still not a fix because the lumber just doesn’t “exist”? Can I adjust the connector plate size if the lumber is not present? The answer to that question is No.
So, how do you determine if the joint calls for lumber replacement? Sometimes this is not apparent until the truss is nearly assembled.
These two photos were taken of the same truss on two panel points. The connector plates were getting ready to be installed. Fortunately, before a commitment was made by plating the webs into the truss, the webs were recut and the very marginal materials were replaced.
At this particular plant, much time has been spent educating the workforce and the plant is dedicated to making an ANSI/TPI 1-compliant product. As the production supervisor planted his face in his hands, my mind was rolling with ideas that would help keep this from happening. Without specific training, monitoring, and education on a constant basis, this sort of serious situation can happen. Of course, a good in-house program can improve and hopefully eliminate this from happening, but as I reflect on the many cases where this is found, I am confronted with the task of how we can explain the problem so that there’s an automatic action when this situation happens.
Here is my attempt to make this simple but important point.
Where wane exists, there is an embedment problem. It’s an air ball. No points scored!
Plating into the area of wane will result in an embedment gap. This gap should not exceed 1/32” if possible. See Table 3.7-1 Tooth Effectiveness.
The following image illustrates this embedment issue. The yellow area would be the depth of the embedment gap. Based on Table 3.7-1, it does not take very much to exceed the 1/16” zone, resulting in a 40% reduction in tooth effectiveness. Just a little bit more at 3/32” it’s a 60% reduction. Basically, in this area, tooth effectiveness is nonexistent. Graphically, this is shown in the illustration as the very top of the wood member, where the top of the curve is over 3/32”.
Does pounding down the plate into the wane area with a hammer improve the situation? Absolutely No. Each plate’s design depends on it being pressed flat.
The Bottom Line
As we’ve discussed in previous articles, Fabrication Tolerances helps us cope with defects. Setting your tolerance to a large number, for example 20%, doesn’t inoculate the builder from considering the impact of wane. Training is required to teach your truss builders to adjust smartly by judging the circumstances carefully. A good rule of thumb is this:
If the wane in the plated area is one-third to one-half of the face of the member, particularly in the plate area, a plate upsize is warranted. If the wane exceeds one-half of the face, then the lumber should be culled.
It’s not simply black or white, however, so careful consideration is required if you want to push your lumber utilization.
An ANSI/TPI 1 3rd Party Quality Assurance Authorized Agent covering the Southeastern United States, Glenn Traylor is an independent consultant with almost four decades of experience in the structural building components industry. Glenn serves as a trainer-evaluator-auditor covering sales, design, PM, QA, customer service, and production elements of the truss industry. He also provides project management specifically pertaining to structural building components, including on-site inspections and ANSI/TPI 1 compliance assessments. Glenn provides new plant and retrofit designs, equipment evaluations, ROI, capacity analysis, and CPM analysis