The phone rang this morning and the caller said that “they had a real quick question.” They went on to ask if “standard truss plates could be used with pressure treated lumber?”
Hmmmm…the questions that some questions prompt. It sort of reminds me of the questions that I used get back when I was a component manufacturer and EWP supplier. I had a sign on the wall behind my desk that simply said $2.00 each. Folks would drop by my office and the first words out of their mouths would be…”How much is …?” and I would point at the sign. Before we could address “How much?” we needed to address the question of “What is it that you need?”, as understanding the scope of work and other expectations surely helped me to answer the question of “How Much?”.
Back to the call this morning; when the caller asked his question. Where did my mind go; as this question prompted the additional questions. The short answer would have been no, but before giving that one out I decided to probe a little deeper.
Questions:
- What exactly is your intended application?
- Why does the lumber need to be pressure treated? Is it really a ground contact situation or wetting and drying?
- If at or near the ground, and unprotected, is it really a good place for truss plates?
- If wetting/drying is occurring, eventually any truss plate will be expelled from the lumber in the swelling/shrinking of the wood fiber that accompanies these cycles. Could this possibly be OK?
- Is the wood exposed to some sort of corrosive environment, outside the corrosive salts used in the pressure treatment of the lumber itself? Is the treated lumber then kiln dried after treatment (KDAT)?
- Will the lumber stay dry in the finished exposure or environment?
I like to end the line of questioning with “Will the lumber stay dry in the finished environment?” as it then begs the question, “If so, why the added expense of PT?”
It just happened that my caller this morning was calling in from Canada, where their standard plates are made from G90 galvanized steel versus the G60 commonly used in the US. That aside, the questions above all still remain. It is well known that the wetting and drying of embedded truss plates will eventually expel them from the wood. If the final application is going to be exterior, or some other scenario where there will be constant wetting and drying, the answer again would be no. What if the application is wet and the embedded truss plates will stay constantly wet? We can design with the assumptions for green (wet) lumber and make the appropriate adjustments for the wood members (see ANSI/TPI 1, Sections 6.4.6 – 6.4.9) but what about the pressure treating chemicals? How corrosive are they in the wet environment? Perhaps then it would be necessary to contact the wood treater to get a definitive answer.
What about other environmental corrosion issues? TPI 1 addresses some in Section 6.5, where we are looking to provide increased corrosion protection to metal connector plates. Remember, when using any of the recognized coatings, all surfaces of the connector plates left exposed (front and back sides of all plates and exposed teeth) must be covered with the selected coating in the minimum thickness recommended by the supplier.
The point is that sometimes we don’t know the correct answer until we dig a little deeper and know exactly what issues we’re dealing with. For me, the short answer is no, and often the long answer is also no, unless we can get a very explicit specification to limit my scope of work risks.
May the New Year bring good health and much prosperity your way.
Thanks for reading, SS
Stan Sias – National Manager
Plated Truss Industry at Simpson Strong-Tie