Do the poles start to rot out after so many years? That depends on whether or not they are pressure treated.
This question was recently posed to me by reader MARK in WOLCOTT. Typically my answer would include some snarky comment such as: “Most certainly, however it might not be during your grandchildren’s grandchildren’s lives!”
The reality is, I know lots and lots of people in the lumber and post frame building industry. Having spent my entire adult life in it tends to add to these. I have yet to meet anyone, who can tell me they have actually experienced a properly pressure preservative treated wood building column rot.
Of course there are always those who have stories such as, “My Uncle’s cousin says he knows of somebody, who knew somebody who had all of their pole barn poles rot off”. Could be – and they probably were not pressure preservative treated at all!
In order to put this matter to rest and ease my already untroubled mind, I utilized the power of the internet and Google to do some research.
Well, it turns out four fine people named Stan Lebow, Bessie Woodward, Grant Kirker and Patricia Lebow got their collective thinking caps together and wrote an article entitled “Long-Term Durability of Pressure-Treated Wood in a Severe Test Site”. Said article was published in Advances in Civil Engineering Materials, Vol. 2 No. 1, 2013 on pages 178-188 (for those of you who want to read it in its full and unabridged glory: https://www.fpl.fs.fed.us/documnts/pdf2013/fpl_2013_lebow001.pdf).
Our team of authors was motivated, as stated in the introduction to the article, by this:
“Pressure-treated wood has been widely used as a durable construction material in the United States for over a century. However, despite its long history of use, there are relatively few reports on the long-term decay and insect resistance of pressure-treated wood”.
Now, as it so happens, the USDAFS (U.S. Department of Agriculture Forest Service) has a test site located near Saucier, Mississippi. The plot has a relatively high annual rainfall and warm temperatures which create a harsh decay environment. Eastern subterranean termites are active at the site. The location is within American Wood Protection Association (AWPA) Deterioration Zone 5, Severe Hazard, which is the most severe hazard classification.
As a control, some untreated posts were placed and all failed in less than three years!
The current Code standard for pressure-preservative treated lumber for structural use is UC-4B (read one of my better articles of all time regarding pressure-preservative treating here: https://www.hansenpolebuildings.com/2012/10/pressure-treated-posts-2/). UC-4B requires a chemical retention for many water borne treatments such as ACZA, CCA-B and CCA-C of 0.60 lb/ft^3 (pounds of chemical per cubic foot of lumber). With retention levels LESS than the current UC-4B requirement, there have been ZERO failures in these chemicals in tests of up to 61 years!
I will stand upon my initial remarks for lifespan.