Rural builders concerned about wood post durability

Friday, August 19, 2022

Different preservatives in pressure-treated wood require producers and contractors to take care when erecting farm buildings

by Becky Dumais

Today's pressure-treated wood may be safer and less harmful to farmers, but a few recent structural failures have some builders worried.

Should Canadian farmers be concerned? And what can be done to ensure farm buildings are being constructed with safe, durable material?

According to the experts, it's all about choosing wood that is treated for agricultural and industrial structural applications.

A shaky situation

Last July, one of Gary van Bolderen's clients called to ask about two jammed windows of a building on a farm property.

Upon inspection, van Bolderen discovered further concerns.

He observed that approximately 24 feet of the building sidewall (near the faulty window), had settled about two inches.

"This caused the window frames to be out of square and the windows to jam," explains van Bolderen, a retired/consulting builder in Springwater, Ont., and charter member of the board of directors for the Canadian Farm Builders Association (CFBA).

It was also discovered that "three of the six-inch by eight-inch pressure-treated posts, which supported the building roof truss system of the pole frame building, had rotted completely. Further observations revealed a fourth post had also rotted."

Seeing this, van Bolderen was shocked.

He's worked in farm building construction since 1972 and never witnessed anything similar. "Having built literally hundreds of pole barns, I've never been asked to replace a pressure-treated post, until just (a few) months ago. That's over 50 years without a known failure."

The building was only 12 years old.

"It would be less surprising if this was observed in a much older building. Twelve years is a very short time. It's so short that I think it would be accurate to describe these as 'temporary' buildings if supporting structural posts only last 12 years," he adds.

After hearing from van Bolderen, Will Teron, a Guelph, Ont. engineer, reached out to contractors, asking if they'd experienced a similar situation. "Instantly, six out of eight responded immediately within an hour saying 'Absolutely'," says Teron.

As he dug into it further, Teron speculated that the rotted posts in the farm buildings were partly tied to the change in chemical formulations and also a lack of industry knowledge of what can and can't be used, whether it's residential or commercial-grade wood.

"It seems as if pre-2003 it didn't matter as much that the residential grades were much better, so if someone was using the 'wrong' grade it wasn't (noticed), but now we're seeing that the residential grades are clearly not suitable for these buildings where we're estimating life expectancies of 40 to 50 years," he explains.

Posts rotting after a few dozen years could be passed off as acceptable in some situations, like a backyard deck – but it's a serious problem for a large farm structure.

It's very different if you've got 60 posts holding up trusses that are 80 feet wide. This isn't a weekend-warrior chore, Teron says. "The risk of any catastrophic failure on a backyard deck is minimal compared to a large on-farm structure."

Teron and van Bolderen have each invested hundreds of hours researching and having discussions with stakeholders.

Since last summer, Teron has spoken with groups such as the CFBA, Wood Preservation Canada (WPC), Ontario building officials, the Canadian Wood Council (CWC), and the Canadian Standards Association (CSA), trying to understand the scope of the issue, what the proper solution is, and how to disseminate the right information. "That's really what we're working on right now," Teron explains.

van Bolderen is aware of two engineering firms that have stopped specifying in-ground application of pressure-treated wood posts, until more information is available and he discloses that three farm building contractors have decided to completely discontinue the use of pressure-treated posts as structural members. "This effectively means they will not recommend building pole frame structures for their client," he adds.

Chemical formulation changes

Canada has had a wood preservation industry for about 100 years. Up until 2004, the dominant preservative for residential and commercial applications was chromated copper arsenate (CCA).

CCA regulations were changed and was banned for residential use, with the exception of permanent wood foundations. According to the CWC, Canadian treaters shifted about 80 per cent of their previous CCA production to ammoniacal copper quaternary (ACQ) or copper azole (CA).

There's an assumption that the chemical change is the cause of early failure.

"We're speculating that's where we're all of a sudden seeing the issue. A residential grade post with (the previous) CCA treatment actually gave pretty good durability, even in commercial buildings," explains Teron. "That post doesn't know if it's holding up a barn or a pergola. But the new treatment chemicals don't seem to be as durable.

"The standards haven't changed dramatically, except that the preservatives used in the residential grade lumber changed dramatically."

"The older treating process has had actual decades of observable evidence for the farm building industry to make knowledgeable decisions on how to use these products," says van Bolderen. "The newer process does not have the same legacy to support its value."

The decayed posts removed from van Bolderen's client's barn still had the tag attached to the bottom, which indicated they were acceptable for ground contact, but intended for residential application and not industrial support. "Thanks to the use of plastic tags, we know it was the right product, as per the use category (UC) system," he says. "I think we're taking the correct view in saying, 'What have we got here and is this a problem?'"

Preservatives in Canada

Natalie Tarini, executive director of WPC, explains that wood preservatives in Canada are governed by the Pest Control Products Acts and must be registered with the Pest Management Regulatory Agency (PMRA) of Health Canada. The PMRA's role is to determine if preservatives can be used safely when label directions are followed and if they will be effective for their intended use.

"If there is reasonable certainty from scientific evaluation that no harm to human health, future generations or the environment will result from exposure to or use of a preservative, its registration for use in Canada will be approved," she says.

Once on the market, PMRA monitors their use through a series of education, compliance and enforcement programs. "Preservatives are also reviewed every 15 years or sooner as new information is discovered and as science evolves," she says.

Equivocal standards & supplies

What is important to note, Tarini says, is that there are specific Use Categories (UCs) for industrial buildings, as defined by Canadian Standards Association (CSA) Group. The UCs for industrial agricultural structural posts are different from the standards for residential projects.

The post classifications under debate by end-users are UC4's subsets of UC4.1 and UC4.2.

UC4 covers treated wood used in exterior construction that's in ground or freshwater contact; UC4.1 covers non-critical components and UC4.2 covers critical structural components or components that are difficult to replace.

If a post is "carrying the 4.1 markings, that only tells me that it's only good for residential and that's really what failed in the first place," notes Wayne Blenkhorn, a mechanical engineer in Shakespeare, Ont., and CFBA board director. "We're suggesting that … it's not working as well as we understood that it should be and there just seems to be some ambiguity in the interpretation of that."

In Teron's opinion, the current standards and guidance are ambiguous.

"It's inconsistent at times," he says. "I can read a document issued by CSA that says for a pole barn … critical building posts need to be UC4.2 standard. But then you talk to WPC and they say 4.1 or 4.2 (can be used)."

Teron contends that customers should not be put in the position where they decide the final product to use. Builders, building departments and engineers are all looking for proper guidance.

The other issue is availability, says Teron. "There's no point in me specifying a purple elephant when they only come in grey.

"We're all looking for clarity. We all want durable buildings," says Teron. "We've been told the higher grades of lumber aren't substantially more expensive, but availability can be an issue. Everyone just wants to know what the standard is and for uniformity across the province and across the country."

Tarini adds, "there is not 'one solution fits all' for specifying structural products as many factors need to be taken into consideration."

Corrections versus consequences

If pressure-treated wood posts have a compromised life, that's a negative consequence for the customer and the builder, according to Blenkhorn. "Because it's a decay situation, I think we would all agree that 12 to 15 years is a premature failure if you've invested in the building," he says.

"On the other hand, it probably took 15 years for the problem to show up. How many more out there are like that? It's important to make the correction now rather than waiting 15 more years and we have another 15 years of posts planted in the ground."

Blenkhorn feels the industry should have the use of a preservative that will preserve the product for 40 or 50 years.

"If you ask most builders, I think most would be satisfied with a 50-year lifespan. The previous chemicals gave that and that's why there had not been a lot of attention until this change occurred."

He doesn't envy those in the industry that are "trying to find the path down the road between the preservative that does the job and satisfies the other. You can see why that path is a little bit windy."

Blenkhorn's cottage deck was built with CCA-treated wood; he says the preservative still seep out when he power washes it and "there have been no structural failures. I just finished building one down at the water and it has newer materials. It looks nicer right now. It's built on a steel deck so I don't have anything in the ground which would hasten the failure."

Those involved in all aspects of construction want to know what to expect and van Bolderen has many questions that he hopes will get answered soon.

"Is the client's investment of millions of dollars going to last longer than 12 years? Can contractors still offer the pole frame structure as the best solution for their client's needs? Will engineers have the confidence in pressure-treated wood to continue stamping the drawings? Will building inspectors approve pressure posts for building permits? Will the insurance industry insure pressure-treated post frame buildings? These are critical questions," he says.

Education for proper application

"I think we need to do a better job of education on pressure-treated products," van Bolderen says. "Such knowledge will prevent future problems. The treating industry, I believe, must do a better job of educating the users about their product.

"The other question is about the post that I put in 12 to 15 years ago. If I order that post today is it the same (quality/type) post? Because they may have changed the spec or something. That's what we're trying to find out."

He hopes the incidents are simply isolated cases, "not a forecast of a wave of hundreds of buildings that are unsafe unless repaired."

Tarini stresses the two most important points surrounding this matter are that it's a specification/application issue and not a product issue.

She uses the analogy of industrial-quality blenders at a smoothie shop. "These are different from your everyday home blender because they serve a different purpose. The same is true for building materials. There are industrial/commercial graded products and residential products. Regardless of the building material in question, if a product is not properly specified for the given application, failure will occur."

Since being alerted to the barn post failure, Tarini says WPC developed an initial communication piece for CFBA membership that defined the different use categories for barn posts as well as provided an overview on the governing standard – CSA 080 for wood preservation.

"After our meeting with representatives from CFBA, WPC and its Standards Review Committee (it was) recognized that there was a need for education on the various applications and specifications that exist in Canada for preserved wood barn posts," says Tarini.

"WPC developed the Specifier's Guide for pressure-treated structural barn posts. Within the document, we include a list of contact information for suppliers, as well as a checklist of points that people placing orders should consider relaying to their supplier, contractor and engineer, to ensure that they receive the correct commercial product."

Professionals like Teron will need to look to the Specifier's Guide to assist in how to properly specify materials as a starting point. "If I walk into my standard lumber yard and ordered a bunch of posts right now, I would probably get residential grade posts, even though they may know it's going to a farm," he says. "We have talked to suppliers."

Teron relays that when van Bolderen told him he'd gone into three lumber yards, describing that he was building a barn and asked for recommendations, "they were all ready, willing and able to sell residential posts. Right from the people who are selling the materials, (they) don't understand the CSA/WPC regulations," Teron says.

Structural barn posts aren't sold at local retail stores, says Tarini. "They do not stock or sell pressure-treated wood that is intended for industrial purposes – such as a structural barn post." In order to make the right choice, she advises working "with an experienced structural engineer when specifying structural products."

More extensive educational efforts are being developed, including a free webinar series in partnership with the CWC and WPC.

The first in the series will take place on Feb. 2 and will focus on the importance of specification and outline the various applications for preserved wood products. "We feel it's important to broaden this education to design and construction professionals throughout Canada," notes Tarini.

Contractors like van Bolderen built their businesses – and reputations – on trust. "My client trusted me when I helped him solve his building needs. I valued that trust then and I still value that today, 12 years after completing his building project," he says.

"I will continue to earn his trust by finding out why the posts rotted so quickly and what he is to expect in terms of the lifespan of his building."

With the industry groups willing to work together and discuss the issue with one another, van Bolderen feels "fortunate that we have all these stakeholders (engineers, contractors, building inspectors, etc.) that are willing to sit around a table and say, 'what is the problem?'

"We're not pointing fingers. I'm very positive about something coming out at the end of a few meetings or a few months of investigation that we're going to have something that the small contractor can say to his customer, but right now we're doing the groundwork. "The bottom line is, the contractor has to have confidence in the product he's (installing) and if we can do that, we'll know where to use it, how to use it. That's what we're working towards," van Bolderen says. BF