Hardwood Lumber

Learn which hardwood types are the most resistant to wood rot.

  • Hardwood
    Burr Oak is one of the White Oak species group.

  • Hardwood

Dan Cassens, professor of forestry and natural resources at Purdue University, has recently developed a CD to help woodworkers and sawyers better understand the characteristics of hardwoods. Lumber from Hardwood Trees includes many “hard-to-find” facts about 35 species of hardwood lumber. Cassens based the information on 30 years of research and personal experience as the owner of a hardwood forest and operator of a Wood-Mizer sawmill.

People frequently say that locust and cedar trees produce decay-resistant hardwood lumber. What is the relative decay resistance of species such as Osage orange, locust, cedar, oak, black walnut and others?

Decay resistance is difficult to address because the resistance of a piece of wood depends on not only the natural resistance of the wood (which can vary) or the effectiveness of a preservative treatment, but also on the exposure conditions of the wood and geographic location. Fence posts are good examples. They often fail due to decay at the ground line. Conditions for wood rot are ideal at this location, but the top part of the post may remain perfectly sound. I have had several 6-inch-diameter black locust posts in place for 25 years in the central Midwest. Two have completely rotted off and some of the others are beginning to show signs of deterioration. If these posts were installed in the Deep South, with warm temperatures and abundant moisture most of the year, I think all of the posts would have failed before now. If they had been installed in the cold North, perhaps none would have failed by now. If installed in the dry Southwest, little evidence of decay would be noted.

Performance expectations are another important factor. If only a year or two of service life is expected, just about any wood can be used. If failure of the wood isn’t life-threatening, standards are usually somewhat more relaxed. The fence posts might be a good example. However, if we were evaluating longer poles that support a deck hanging over a deep, rocky ravine, we have an entirely different issue. Failure could result in injury, and the deck is also subject to building code restrictions, which will likely require pressure-treated lumber.

We can further increase expectations by considering a cross-country power line with wood poles. These lines are expensive to build and failure of just a couple of poles could result in serious outages of power to a large number of people. In these applications, standards for treatment are carefully followed and quality control checks are performed. Expectations are for decades of service.

The Wood Handbook uses three categories to rank the natural decay resistance of heartwood. These are (1) resistant or very resistant, (2) moderately resistant and (3) slightly or nonresistant. Assuming preservative treatment is not acceptable, choose only wood from the resistant or very resistant category if the wood is to be used where a decay hazard exists. These include the heartwood of all commercial cedar, black and honey locust, osage orange, white oak, black walnut and others. Black locust and osage orange have a particularly high resistance to decay.

Stick Trade_2
3/4/2010 3:56:46 PM

Great article about hardwood lumber. Stick Trade is a great resource for worldwide buyers and sellers of all kinds of lumber. Check out http://www.sticktrade.com/ for our wholesale listings of lumber, logs, plywood, flooring, veneer and more. Also, check out our partner site Woodanew.com at http://woodanew.com/ . We are a leading reclaimed wood products exchange web site. We bring together buyers and sellers of antique beams, barnwood, reclaimed flooring, and salvaged lumber. Let's live wisely and share resources.

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