Tag Archives: AWPA

Pressure Treated Douglas Fir

Pressure Treated Douglas-Fir

Reader ERIC in SANTA CRUZ writes:

“Hello, I am researching pressure treated pole and post treatments. I am looking at UC-4b treatment for long term. I need real life experience with Douglas fir using CCA-C . The other consideration is Douglas Fir using ACZA.”

Mike the Pole Barn Guru says:

Early in my post frame building career, I worked for Lucas Plywood and Lumber in Salem, Oregon. Owner Virgil Lucas would (about once a month) have our lumber yard crew gather up all dimensional lumber beginning to have a ‘sun tan’ (turned grey from being outdoors in weather) and send it off to be CCA pressure treated. His thought was this would hide discolorations. Well, hiding off color was correct, however much of this lumber was Douglas-fir and ended up basically being painted green from chemical preservatives, but actually not being anything close to adequately treated.

Today most CCA is composed of a mixture of oxides of chromium, copper and arsenic. Each component has a specific function — copper as a fungicide, arsenic as an insecticide, and chromium as a bonding agent, which “fixes” everything to wood. CCA treating mixture is supplied as a liquid concentrate, is diluted with water to appropriate level and then injected into wood under high pressure in large steel treating cylinders. After wood has absorbed all of the treating solution it can absorb, pressure is removed and a short vacuum is applied to pull off excess liquid. This wood is then air- or kiln dried before being shipped to lumber yards.

Once inside wood’s cellular structure, CCA treating solution undergoes a complex series of chemical reactions with major wood components — cellulose, hemicellulose and lignin. These reactions result in a bonding of CCA ingredients to wood fibers, rendering these chemicals insoluble and resistant to water-leaching. 

In order to accept CCA preservative solution, green lumber is usually dried to a moisture content of 25% or less. This is accomplished by either kiln drying or air seasoning. During treatment, wood fiber becomes completely saturated with preservative solution, being mostly water. After the treatment process is complete wood is still virtually 100% water saturated.

Highest grades of treated wood are kiln dried after treatment to bring moisture content down to 19% or less. However, it is more typical to allow this wood to air dry to reach equilibrium moisture content. In some cases treated wood will reach lumber yards while still very wet.

Many types of softwood can be pressure treated with CCA preservative; however, the most commonly treated species is Southern Yellow Pine. In the West, Hemlock, Hem-fir, Ponderosa Pine, Jack Pine and Red Pine are also subject to CCA treatment. Some species, such as Douglas fir, have difficulty accepting waterborne treatments; these are said to be refractory. To promote penetration of preservatives, these woods are sometimes mechanically incised before treatment. Treated lumber will then have characteristic rows of incising marks. (Read more about incising here: https://www.hansenpolebuildings.com/2014/08/incising/).

American Wood Protection Association (AWPA) set standards for United States pressure-treated wood. These standards set requirements for preservative level in wood, depth of penetration, treatable species and other important treating parameters. Adherence to standard is checked by way of third-party inspection at treating plants. Those treaters who consistently meet AWPA standards are allowed to display AWPA and third party inspection agency marks on their lumber.

Treated lumber will also often bear a grade stamp and a mark designating level of CCA treatment. Grade stamps are similar to those for untreated lumber. CCA level is listed as a retention number, which represents pounds per cubic foot (pcf) of preservative in wood. For above-ground applications specified retention of CCA is 0.25 pcf, for ground contact uses it is 0.40 pcf, and for structural in ground use it is 0.60 pcf.

Fixation and leaching characteristics of chromated copper arsenate (CCA)-treated Douglas-fir sapwood and heartwood have been evaluated using expressate method and American Wood Protection Association (AWPA) El 1-97 leaching procedure. CCA fixation, monitored by hexavalent chromium reduction, was much faster in heartwood than in sapwood; copper and arsenic fixation in heartwood appeared to be incomplete, regardless of duration of fixation time. Poor fixation of copper and arsenic in heartwood was confirmed using leaching tests. Based on results, it has been concluded CCA is not an appropriate preservative for Douglas-fir heartwood because of its poor fixation quality.

Due to this, ACZA remains the first choice for pressure treating Douglas-fir. You may want to consider the use of Hem-fir treated to UC-4B standards with CCA, MCQ or MCA due to pricing and availability issues.

Canada Facing Premature Decay of Pressure Treated Columns

Canada Facing Premature Decay of Pressure Treated Columns

Fear of properly pressure preservative treated wood decaying prematurely has been a continuing concern amongst potential post frame building owners. Key to this is “properly” and at issue how pressure treated wood is labeled and sold at the retail level. Canada uses AWPA’s (American Wood Protection Association) Use Category system where UC-4 tags say “Ground Contact” without clearly indicating to purchasers UC-4A (prevalently in stock at lumberyards and big boxes) as being inadequate for structural in ground use.

I have been shouting out in regards to this for years, with no noticeable results. https://www.hansenpolebuildings.com/2014/05/building-code-3/

The following article by Don Wall appeared in the Daily Commercial News of November 15, 2021

C GARY VAN BOLDEREN — Former CFBA president Gary van Bolderen learned in July that three six-inch-by-eight-inch pressure-treated posts installed to support the roof truss system in a building his firm had built had rotted completely after just 12 years.

Reaction has been swift and stakeholders have swung into action after concerns were raised by former Canadian Farm Builders Association (CFBA) president Gary van Bolderen and others that some types of pressure-treated wood manufactured after 2003 are prematurely rotting in the ground.

In July van Bolderen, now retired as owner of Dutch Masters Construction of Barrie, Ont., received word from a former client that a pole frame building his firm had constructed just 12 years ago was shifting. It was soon determined that three six-inch-by-eight-inch pressure-treated posts, installed to support the building’s roof truss system, had rotted completely.

Since then, van Bolderen and fellow former CFBA president Will Teron, a building engineer who has credentials as a contributor to the National Building Code, have spent hundreds of hours researching the evolution of pressure-treated wood, even visiting a number of lumber yards to determine how well suppliers understood the proper application of the half-dozen or so types of pressure-treated wood that are available.

As a result of their persistence, there was an online call held Nov. 2 involving executives and experts from the Wood Preservation Council (WPC), members of a newly formed CFBA task force and van Bolderen and Teron. Action plans were hatched by both the WPC and the CFBA task force.

Van Bolderen believes the cases he has found in his initial inquiries could be “the tip of the iceberg.”

“As a builder, we don’t know how widespread the actual issue is or how many failures there are going to be, but the problem is, the confidence is gone,” said Brian Brubacher, co-chair with Wayne Blenkhorn of the CFBA task force. “I need to know what I’m buying when I go to my local lumber yard.”

Blenkhorn commented, “I think we have to be careful not to create just general panic…We don’t want everybody to go and be drilling holes in their posts next week.”

The parties have determined the issue stems from a 2003 decision to withdraw certain treatments of pressure-treated products because of fears they caused cancer. When lumber yards stopped stocking that type of wood there was little education on the part of the WPC, the CBFA, manufacturers or distributors to ensure farm builders or other users understood the new set of options and what products were rigorous enough to withstand below-ground use in a commercial building.

That education deficit has continued to today, the stakeholders agree.

Further complicating matters is the categorization of the wood. Teron explained among several standards there are two commercial standards, 4.1 and 4.2, for low-decay and high-decay environments. The WPC is working with the Canadian Standards Association (CSA) to better define those terms, but the residential application has a confusingly similar designation, 4.1 D.

Van Bolderen said he had no complaints of rotting in 50 years until July, with post-2003 wood failing.

“There’s nothing wrong with pole frame as long as it’s the right product. I think there’s a real disconnect between the producer, the retailers, the engineers and the builders about what is the right product,” he said.

“I was absolutely shocked that the posts were deteriorating completely.”

After being alerted to the barn post failures, the WPC developed an initial communication document for CFBA members that defined the different use categories for barn posts and provided an overview on the governing standard, which is CSA 080 for wood preservation.

The WPC will undertake education and outreach that will include a new publication outlining the differences between residential and commercial or industrial pressure treated products and a list of outlets where the proper posts can be obtained.

There will also be webinars held in conjunction with the Canadian Wood Council, and third-party agencies will be consulted, said WPC executive director Natalie Tarini.

The WPC has “recognized that there is a need for education on the various applications and specifications that exist in Canada for preserved wood barn posts,” said Tarini.

“It is important to note that this is a specification/application issue and not a product issue.”

Meanwhile the CFBA task force is preparing an immediate survey for its members to identify other reported failures and other experiences; and it is tracking the changes in treatments over the past 20 years including what supplies are currently being stocked and delivered.

“Clearly our objective is an early advisory to our members of a reported concern that PT posts as used may not be living up to expectation,” said Blenkhorn. “At the same time to establish which products can be manufactured and at what cost to meet this needed life expectancy.

“We feel that we need to send a notice to all the builders now that if you have immediate plans for framing construction, please, please address this with your engineers.”

Teron noted with approval that the WPC is involving technical members of its standards committee and the WPC president.

“We had a really good, frank, direct discussion,” said Teron. “No-one’s pointing fingers. Everyone’s saying we need to move this forward. We need to improve the education so we have an understanding and everyone’s using the effective parts.”



Reader MIKE in ORLANDO writes:

“Dear Pole Barn Guru,

I bought a 38×42 Pole Barn kit from a reputable supplier. The posts are 8″ x 8″ – but do not have the AWPA markings that you describe in your Blog. These posts have a tag stapled to the end that says “SPLASHWOOD, Saltwater Splash Use Only, .80 PCF, Chromated Copper Arsenate (CCA-C), Southern Wood Preserving, Inc,.” and a paragraph of cautions and Consumer Information. I tried to look up this info to see if these posts are AWPA UC4B equivalent but could not find any info on-line.
Are these post acceptable for my Pole Barn construction?

Mike the Pole Barn Guru writes:

Splashwood™ happens to be a registered trademark and brand of Great Southern Wood Preserving, Inc., and was filed December 30, 2004. Great Southern Wood Preserving, Inc., is based in Abbeville, Alabama and was founded in 1970. It has 15 plants located in Alabama, Arkansas, Florida, Georgia, Mississippi, Missouri, Louisiana, Maryland, Virginia, Pennsylvania and Texas with annual revenue of a billion U.S. Dollars.

Pressure-treated wood is treated to various retention levels which are intended to protect the wood for particular applications. Retention levels indicate the amount of preservative retained in the wood in a specific assay zone. In North America, retention is expressed in pounds per cubic foot (pcf).

Retention levels or treating quality procedures are marked on pressure treated wood. The AWPA (American Wood-Preservers’ Association) outlines retention levels required for various applications.

Retention varies with depth in the wood, so preservative penetration also affects wood longevity. In species with large amounts of sapwood, such as southern and red pine, the preservative must penetrate 2.5 inches or 85% of the sapwood to meet standards.  In western species which are predominately heartwood, the wood is incised to ensure a treated shell, and any cut surfaces should be field-treated with a preservative containing at least 2% copper (read more about cut ends of treated lumber here: https://www.hansenpolebuildings.com/2014/09/pressure-treated-lumber-2/).

To meet the Code required standard of UC-4B for structural timbers, takes a retention of 0.60 pcf with CCA. The pressure treatment of your columns exceeds the minimum requirements.


Incising Lumber


My former wife (mother of my two youngest children – Allison and Brent), was by training an RDH (Registered Dental Hygienist). In order to keep her registration current, she had to obtain CEUs (Continuing Education Credits). One way to generate CEUs was to attend the annual state dental convention.

One year I went along with her and as we perused the trade show floor, the assumption was somehow made of me being a dentist – so I received lots of attention. Also tons of free stuff – I don’t think I needed to purchase a tooth brush, tooth paste or dental floss for the next decade!

Other than my annual visits to the dentist, about the only thing I remotely knew in regards to teeth were the incisors are the front four teeth on the top and bottom.

With my tremendous knowledge of incisors – I was able to easily translate to incising of lumber.

For those in the east and south – you may have never seen pressure preservative treated lumber which has been incised. Most treated lumber in those regions is Southern Yellow Pine – which is highly treatable (think of it as being a chemical sponge).

Travel west and north, the lumber species of choice for pressure treating is grade stamped as Hem-Fir. Hem-Fir is not a species unto itself, it is a lumber species “group” which includes California Red Fir, Grand Fir, Noble Fir, Pacific Silver Fir, Western Hemlock and White Fir.

Incised LumberDifficult-to-treat (refractory) lumber species, such as Hem-Fir, must be incised prior to preservative treatment to meet minimum penetration requirements for preservative-treated wood. Incising is a pretreatment process in which small incisions or slits are punched into the wood. To me, the resultant product looks as though the lumber has been walked on by someone wearing golf shoes!

Incising increases preservative retention and penetration during the treating process by increasing the amount of exposed, easily penetrated end-grain and by decreasing the side-grain surface area. While incising has been used since the 19th century, the process appears to have developed casually with little consideration given to optimizing the process to maximize preservative treatment and minimize strength loss. While AWPA (American Wood Preservers Association) standards require incising, they do not define or recommend what type, how deep, or how many incisions are required. Generally, it appears the more effective an incising pattern is in achieving preservative penetration, the more it reduces strength.

AF&PA’s National Design Specification® (NDS®) for Wood Construction includes provisions for the downward adjustment of lumber strength characteristics for incised lumber by use of an Incising Factor known as Ci. Referenced design values are multiplied by Ci when dimension lumber is incised parallel to grain a maximum depth of 0.4”, a maximum length of 3/8”, and a density of incisions up to 1100 per square foot.

E values are to be multiplied by 0.95, while other values (with the exception of compression perpendicular to the grain of the wood) are multiplied by 0.80.

Sound engineering design of incised lumber (which includes pole building columns) take into account these strength reductions.

If you see Hem-fir and it has all these little cuts – don’t panic. It just means it’s been incised for adequate infiltration of chemical treatment. This ensures preserving a longer life of whatever you are building, be it a deck, garage or even a new pole building house.