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Component Manufacturing dverti$er
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Don’t Forget! You Saw it in the
May 2017 #10214 Page #76
Treated Lumber and Trusses (and the One Condition Under Which MPC Wood Trusses Shouldn’t Be Used) By Kelly Sias, P.E., Simpson Strong-Tie®
What do a chicken house, a water treatment plant and a raised wood floor system all have in common? Very likely, they all involve preservative-treated lumber. They’re also all examples of common environments in which preservative-treated, metal-plate-connected (MPC) wood trusses may be specified. Although trusses are successfully used in a variety of environments that require treated lumber, the first mention of “treated lumber” usually sends up a red flag in a truss design office. While the corrosion protection of truss plates is no different from the corrosion protection of any other steel fastener or hanger that comes in contact with treated lumber, there are a few more considerations that come into play whenever treated lumber is going to be used in a truss application. When fire-retardant-treated lumber or preservative-treated lumber is specified, the first (and easiest) step is to determine whether standard G60 truss plates are acceptable for use with the treated lumber, or whether the chemical treatment requires additional protection of the plates. Recent articles on our S.E. Blog have Raised Wood Truss Floor System discussed how fasteners are evaluated for corrosion resistance and how the Corrosion Resistance Classifications in our catalog help facilitate selection of hardware and fasteners for different types of treated wood and environmental conditions. Similar guidelines are also available for determining the proper metal connector plate for different wood treatments. For example, when using the sodium borate-based preservatives and fire retardants, standard G60 galvanized metal connector plates are acceptable. However, ammoniacal/alkaline/amine copper quaternary preservative types require more protection, such as G185, ASTM A153 galvanized- or stainless-steel truss plates. The complete guidelines – Quick Guide for Alternative Preservative Treatments with Metal Connector Plates – are available from the SBCA website. When trusses are used in particularly corrosive environments such as coastal environments or salt storage buildings, the ANSI/TPI 1 standard lists coatings that will provide increased corrosion protection for the plates (see below).
6.5 CORROSIVE ENVIRONMENTS 6.5.1 Recognized Coatings. The following coatings are recognized as providing increased corrosion protection to Metal Connector Plates: (a) Epoxy-Polyamide Primer (SSPC-Paint 22). (b) Coal-Tar Epoxy-Polyamide Black or Dark Red Paint (SSPC-Paint 16). (c) Post-plate-manufacture hot dip galvanizing per ASTM A153.
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Truss Plate Corrosion from Treated Lumber
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