9.1 Reducing Corrosion Rates

Standard connectors are intended for inland uses, and under normal conditions, they last as long or longer than other materials in a building. Although components of some buildings in coastal communities may have only slightly increased corrosion rates, buildings close to the ocean are likely to have drastically higher corrosion rates. In nearshore areas, the use of more corrosion-resistant materials and coatings is recommended in partially sheltered exterior exposures, open exposed exterior exposures, vented enclosed exposures, and unvented enclosed exposures (see Figure 6). Use of nominally galvanized metal connectors should be limited to interior areas that can be protected from corrosion (interior living space exposures).

Additional considerations in reducing corrosion rates are as follows:

• Consider changing the exposure class where connectors are used. For some uses, corrosion rates can be reduced by altering the exposure of the connectors. For example:
  
  • Connectors typically found on building exteriors should be fully covered if possible or otherwise protected from salt spray and moisture. Applying exterior siding to fully cover the connections is one way to change the exposure from open exposed exterior exposure to an unvented enclosed exposure condition.
  • An easy way to protect joist hangers and truss plates in the floors of piling-supported buildings is to sheath the underside of the floor joists to reduce the exposure to salt air. Adding such sheathing transforms one of the worst exposures, partially sheltered exterior exposure, into the less corrosive unvented enclosed exposure condition. However, when corrosion occurs, it can go undetected, so screws or some other removable fastening mechanism should be used to allow periodic inspection.
• Consider using alternate materials or connection methods. For some connections, such as floor joistto-floor beam connections, corrosion may be minimized by not using light gauge metal connectors, especially in partially sheltered exterior exposures and open exposed exterior exposures. Construction practices that were commonplace before the advent of light gauge metal connectors can be used to connect wood framing. With many of those practices, metal fasteners (nails, wood screws, lag screws, and bolts) are used with wood framing, and the metal fasteners are nearly fully concealed and protected from the elements by the wood components. In many connections, only the head of the fasteners remain exposed to salt spray. When used with preservative-treated lumber, stainless steel nails and other corrosion-resistant fasteners should be used. See Section 9.2 for more guidance on maintenance and replacement. See the applicable building code for information on when these alternate methods are permitted and the size and number of fasteners that are required.

Figure 9 and Figure 10 show common methods of connecting wood framing members with only nails, screws, lag screws, and bolts. In both methods, the shafts of the fasteners are not exposed to salt spray.

The drawback of these methods is that their capacity to resist loads is not readily known since their strength depends greatly on fastener sizes and even more on the species of wood used. The design of wood framing connections is complex, and prescriptive methods are somewhat limited. The IRC and the Wood Frame Construction Manual (AWC, 2015) both contain nailing schedules, but neither contain prescriptive methods for connections such as those shown in Figure 10 and Figure 11. In contrast, the capacities of light gauge metal connectors are published by the manufacturers and verified by third-party testing. See the textbox below for more information.