Tag Archives: wood decay

Cedar or Redwood Posts for Pole Buildings?

More than once (especially in California), it has been suggested by lumber yards to use cedar or redwood posts for pole buildings, rather than pressure preservative treated wood of other species. The lumber yard sales people are of the belief the cedar or redwood posts should have adequate natural resistance to decay to last the lifetime of the building.

At home, one of my own pole buildings has a cedar deck on top of it (yes, on top, which is the topic for a future blog). About 15 years old, many of the redwood deck boards had to be replaced last summer, as they had decayed to the point of being unsafe.

In the 1994 Encyclopedia of Agricultural Science, Jerrold E. Winandy wrote, “It is commonly recognized that heartwood lumber from these well-known commercial species contains extractives that are toxic to a variety of wood-decay fungi:  “Heartwood forms as the living sapwood cells gradually die.  In some species, the sugars present in the cells are converted to highly toxic extractives that are deposited in the wood cell wall.  Many species produce durable heartwood, including western red cedar, redwood, and black locust; however, durability varies within a tree and between trees of a given species.”

In contrast, “sapwood of all species has little resistance to deterioration and fails rapidly in adverse environments.””

In 2005, Professor Paul Fisette of the University of Massachusetts Amherst wrote an article titled ‘Wood Myths: Facts and Fictions About Wood‘, which warned consumers against the myth all cedar and redwood are rot resistant:   “Like fingernails on a blackboard, homeowners bubble, ‘I have cedar siding.’  Don’t get me wrong, cedar is my choice for siding too, but let’s get something straight.  Not all siding, decking and trim made from cedar, redwood or other species famous for durability are in fact rot resistant.  Only the heartwood of certain species is naturally decay resistant.  Untreated sapwood of virtually all species has very little decay resistance.  You can expect a short service life if you use sapwood in decay-producing exposures.  Large old-growth trees are a thing of the past.  We now harvest smaller second growth material that contains a high percentage of sapwood.  Heartwood lumber is essentially unavailable in many species.  Specify ‘all-heart’ and you may be in for a dose of sticker shock. But if durability is important to your design, you should make heartwood part of your budget.”

Professor Fisette was writing about cedar and redwood for use as siding, which is a strictly an above ground application. The use of cedar or redwood posts for structural in ground use appears to be nothing short of a recipe for disaster, or at the very least, dissatisfaction when the columns decay and must be replaced.  And that, my friends, comes from the voices of experts when it comes to decay and rot in cedar or redwood posts.

How Untreated Wood Decays – Pressure Treated Wood Prevents Decay

I get asked nearly every day about the lifespan of pressure treated wood. Prior to expounding upon the virtues of pressure treatments, it would be helpful to know more about why untreated wood decays. With this information in hand we can see how current chemical treatment methods prevent wood decay.

The following is excerpted from a paper found at www.slideruleera.com

weathered pole barn

Weathered Pole Barn

“All decay of wood is caused by fungi, low forms of plant life that develop and grow from spores just as higher plants do from seed. These microscopic spores abound everywhere in open air. Lodging in favorable places on untreated timber with which they come in contact, they germinate, sending out hyphae, or strands, that spread through the wood. These plant-like growths break down the wood substance, converting it into food required by fungi for development. However, like all forms of plant life, the spores of wood-destroying fungi must have air, suitable moisture and favorable temperature as well as food if they are to develop and grow. Deprived of any one of these four essentials, the spores cannot develop and the wood remains sound, retaining its full strength for many years of useful, low-cost service.

Wood submerged in fresh water cannot decay, because the necessary air is excluded; decay also will not progress in wood with moisture content less than 20 percent of its weight. Advancement of decay is progressively checked as temperatures drop below those generally favorable for plant growth, and all fungus activity stops as freezing temperatures are approached. Progress will resume, however, once favorable climatic conditions are restored. Because it is impractical to exclude air and moisture from, or to control temperatures in, most outdoor or exposed structures, effective preservation is attained by impregnating the wood with chemicals which are poisonous to fungi, insects and marine borers.

Spores of fungi may lie dormant in the crevices of untreated wood for years while conditions for development remain unfavorable, only to spring to life and begin their destructive activities whenever favorable growth conditions are restored.”

In a later blog, I will discuss the treatments for wood to preserve the longevity of posts and other lumber in contact with the ground.  There is an interesting story of the evolution of what “works” and what is “approved”, so stay tuned.