General

At a moisture content of greater than 25 %, wood is subject to fungal attack or decay. Decay will be rapid when the temperature is in the range of 70 to 85⁰F. The potential for wood decay when exposed to the outdoors, therefore, varies in accordance with climate (refer to Decay Hazard Map, Figure 4–2). However, wood exposed to excessive moisture within a building assembly in any climate, particularly one with a low drying potential (see Chapter 4), will grow mold and rot.

There are essentially three options for preventing decay of wood which may be exposed to the elements:

• Protect (or separate) wood from moisture
• Use naturally decay-resistant wood
• Use preservative treated wood

Of equal concern is the corrosion resistance of fasteners that must hold wood joints firmly together. Corrosion of insufficiently protected metal fasteners can eventually lead to complete failure of key fasteners which support assemblies like deck joists.

Finally, it is important to consider cost-effective alternatives to wood that offer potential durability and maintenance benefits. In combination with measures presented earlier in this course, particularly in Chapter 4, recommendations in the following section should address the major concerns regarding durability of wood construction.