How Methods for Preserving Wood Have Evolved and Why It Matters for Pole Buildings
A chain is only as strong as its weakest link; pole buildings are simple by design, so there aren’t all that many “links” that can pose issues.
The point of failure for pole buildings usually occurs underground. The buried posts can rot or even break as the result of a hinge point. Regardless of the reason, it’s clear that a pole building won’t reach its full potential lifespan if the wood posts don’t maintain their integrity.
Fortunately, industry pros have known for decades that wood posts need to be properly preserved to ward off rot and insects. The methods for treating pole buildings’ posts have evolved more than once over the last hundred years, and you’re bound to feel more confident about your building’s longevity once you’ve learned about modern guidelines.
Why Is Treated Wood So Important?
As we mentioned before, part of pole buildings’ appeal is their simplicity—there just aren’t that many materials involved in the construction process, so there aren’t many items that could cause problems down the line.
The metal cladding on these buildings is made of steel, and so it’s unlikely to create even long-term issues; the girts and purlins are protected from the elements, and they’re engineered to sustain the loads that they bear, so they aren’t a frequent area of concern.
This being the case, the buried sections of a pole building’s posts are often considered the “weak links.” As a result, International Building Code (IBC) has specific guidelines for ensuring that wood poles stand the test of time, but this hasn’t always been the case.
How Have Wood Treatments Evolved Over Time?
Back when pole buildings first rose to popularity in the 1930s, farmers used recycled telephone poles to build their structures; these poles were treated with incredibly high levels of creosote. While this was effective as a preservative and pesticide, it was also a toxic carcinogen, which is why creosote is not approved by the EPA to treat wood for any sort of residential use today.
In the 1940s, chromated copper arsenate (CCA) became a popular wood preservative for pole building posts. As you may have been able to guess, the “arsenate” in “chromated copper arsenate” refers to arsenic, so (much like creosote), CCA can be unsafe for human contact, and it was banned for residential construction starting in 2003.
Fast forward another couple of decades, and there are a number of different preservatives that are now used to ensure poles are both safe and durable, but Alkaline Copper Quaternary (ACQ) and Copper Azole type C (CA-C) are two of the most common.
Who Issues The Guidelines for Treating Wood?
Since the early pole building days, codes concerning treated wood poles have advanced considerably. The IBC and the American Wood Protection Association (AWPA) now outline the standards for treating wood posts.
Today, section 1807.3 of the IBC concerning embedded posts and poles says that “wood poles shall be treated in accordance with AWPA U1 for sawn timber posts (Commodity Specification A, Use Section 4B).”
This particular section of the AWPA standards defines UC4B as heavy duty ground contact materials that are critical to the structure and exposed to all weather cycles with a high risk for decay—that’s a pretty perfect definition for pole building posts.
What this means is that builders can easily check with their lumber suppliers to ensure that the wood they’re using for pole building posts is rated as UC4B and preserved as such. In turn, you gain the peace of mind that your posts won’t simply rot in a few years.
How Are Wood Posts Treated?
It’s not just guidelines and preservatives that have evolved over time, it’s also the way that the wood is treated.
Today, we are able to pressure treat wood with more effective processes than ever to achieve optimal preservative retention. The pressure treatment process is carried out in just a handful of steps:
- Once a load of untreated lumber has been added to the treatment cylinder, all of the air is eliminated with a vacuum pump.
- Next, the treatment tank is filled with a solution consisting of water and preservative.
- When the treatment cylinder is full and the lumber is submerged, a pressure pump is used to pressurize the tank.
- After the pressure cycle ends, any remaining solution is drained into a storage tank.
- With all of the solution drained from the treatment cylinder, a final vacuum cycle is initiated, then the lumber is removed.
AWPA code requires that UC4B wood has a .60 retention of the preservative; the pressure treatment method outlined above makes it possible to confidently meet that standard.
How Does Pressure Treated Wood Impact Pole Buildings?
Hopefully we’ve made it clear by now that preserving posts effectively eliminates the biggest threat to pole buildings’ life spans. Basically, pressure treated wood that uses modern preservatives is one of the key things that enables you to enjoy your pole building for decades to come.
Now that you have an in-depth understanding of what goes into preserving the structure of these buildings, we hope that you’ll feel more confident as you decide whether to invest in a pole building of your own; contact us today to talk through the details of your dream building!