A trip down the fastener aisle at the hardware store can be a bit overwhelming if you are unfamiliar with the many types of fasteners. If you have guessed that fasteners and connectors for exterior use may need to be different than those for interior use, you would be correct.
Exterior fasteners and connectors include nails, screws, bolts, nuts and washers, joist hangers, flashing, angles, brackets, post anchor ties, and other construction hardware, and, are used in the construction of a myriad of residential outdoor projects such as decks, porches, arbors, garden sheds, and fences. They need to be highly corrosion-resistant because they will be exposed to air and moisture, salt (in coastal areas), and in some situations, wood preservatives.
Common fasteners used in outdoor construction are made of stainless steel or are fabricated from steel or iron and then a hot-dipped galvanized coating is applied. Common connectors used in outdoor construction are typically galvanized. Using fasteners and connectors that are not highly resistant to corrosion will create a weakened connection when exposed to the elements. Building codes typically require corrosion-resistant hardware for exterior structural use.
Hot-dipped galvanizing is a process where metal fasteners and connectors are dipped into a bath of molten zinc. The zinc forms a uniform corrosion-resistant coating over the entire surface, getting into all crevices, and forms a high strength cover that protects the steel or iron from the elements. This process has actually been used for about 150 years.
Use hot-dipped galvanized fasteners with hot-dipped galvanized connectors. Placing hot-dipped galvanized items in contact with stainless steel can cause the zinc (galvanizing) to corrode.
What Fasteners and Connectors to Use for Specific Types of Wood
Woods with Natural Resistant Properties
There are several types of wood for exterior applications that is used for their natural resistance to decay and insects including redwood, cedar, and ipe.
- Redwood – According to the California Redwood Association all fasteners, connectors, and other metal hardware should be stainless steel, aluminum, or high quality hot-dipped galvanized
- Cedar – The Western Red Cedar Lumber Association recommends using corrosive resistant fasteners, connectors, and other metal hardware, including stainless steel, aluminum, or hot-dipped galvanized
- Ipe – For those unfamiliar with Ipe, it is a highly durable Brazilian hardwood rated for 25+ years, and creates a gorgeous deck. Self drilling stainless steel screw is the recommended fastener. Galvanized fasteners can be used, but stainless steel will eliminate chemical reaction or staining of the wood that can occur with using galvanized fasteners. Also, using stainless steel fasteners will provide a longer service life of the wood. Because of Ipe’s density, pre-drilling a pilot hole and countersink is required to avoid splitting, even with self drilling screws.
- For any construction hardware, always follow the manufacturer’s recommendations for the use of their product(s).
Treated wood is wood that does not have natural resistance to decay and insects that the woods listed above have. So to be used in exterior applications it must be pressure treated with a preservative to give the wood protection against decay and insect damage. This is a process where the preservatives are forced into the cells of the wood under high pressure moving the chemicals further into the wood for greater protection. The newer ACQ (alkaline copper quaternary) preservative, used today for residential lumber use, replaced the CCA (chromated copper arsenate) preservative in 2004. The additional copper in the ACQ preservative makes it more corrosive to construction hardware, so the fasteners, connectors, flashing, etc. used with it must be highly corrosion-resistant.
- Treated, or pressure-treated wood – Very common in exterior applications, especially for ground contact. The International Residential Code specifies the following: Hot-Dip Galvanized fasteners (meeting ASTM-A153) and connectors (ASTM-A653 Class G-185 sheet, or 304 or 316 stainless steel). Type 316 stainless steel provides the highest level of corrosion protection, especially in salt exposure environments. Aluminum hardware of any type is not recommended for direct contact with treated wood.
- Always follow the manufacturer’s recommendations for the use of their product(s)
Purchasing hardware for a DIY project with these specifications for use with treated wood, should not be a difficult venture for you. Manufacturers such as Simpson Strong-Tie, make high quality exterior hardware for use with treated wood. They can be called for assistance in purchasing the correct hardware for a project; also, ask where the nearest retailer is to you that carries their products – likely it will be a big box store and/or a lumber yard.
Don’t forget about your local building lumber yards – they can be a good source for various materials for many home improvement projects.
Photo credit: Simpson-Strong-Tie