Pressure Treated Posts: 1807.3.1

Not near as exciting as 867-5309, but this one Section of the International Building Code (IBC) is one of the most important and least understood sections.

The American Wood Preservers Association (AWPA) addresses in, Section UC4 wood, which is pressure preservative treated for “Ground Contact”. The “UC” is short for “Use Class”.

UC4A is for “General Use”. This is “Wood and wood-based materials used in contact with the ground, fresh water, or other situations favorable to deterioration. Examples are fence posts, deck posts, guardrail posts, structural lumber, timbers and utility posts located in regions of low natural potential for wood decay and insect attack.

UC4B is for “Heavy Duty”. This is “Wood and wood-based material used in contact with the ground either in severe environments, such as horticultural sites, in climates with a high potential for deterioration, in critically important components such as utility poles, building poles and permanent wood foundations, and wood used in salt water splash zones.”

Neither of these clearly identifies which degree of pressure treating should be utilized for structural in ground use – to support a post frame (pole) building.

When the first IBC was published in 2000, Section 1805.7.1.2 stated, “Wood poles shall be treated in accordance with AWPA C2 or C4. This language remained the same in the 2003 IBC. The AWPA C2 and C4 standards have been withdrawn, therefore are no longer applicable or referenced standards in later editions of the Code.

In the 2006 IBC, however, things changed. Section 1805.7.1 states, “Wood poles shall be treated in accordance with AWPA U1 for sawn timber posts (Commodity Specification A, Use
Category 4B) “. In the 2009 IBC (and repeated for the 2012 edition), the language remained the same, however the referenced section of the Code is now 1807.3.

What does this mean for the average consumer who is shopping for a new pole barn? Everything!

Visit the local lumberyard, or big box lumber store. Take a walk through the pressure treated lumber department. Every piece of pressure preservative treated lumber has a tag on it. This tag identifies who the pressure treater was, as well as the level of pressure treating. Sadly, most of the pressure treated posts will be treated only to UC-4A….which does NOT meet with the Code requirements for use in pole buildings! It is very likely the lumberyard sales people do not realize this to be the case.

Even more frightening, most Building Officials are unaware of this requirement!

When shopping for a new pole building, ask what level of pressure treatment the pressure treated posts are treated to. If the company being contacted does not know, will not tell, or says they are “treated for structural in ground use” (or similar language), or anything other than UC-4B…run, do not walk away!

In order to have a Code conforming building, and one which will last the lifetime it is designed for – demand a minimum UC-4B pressure treating level for all structural load bearing columns.

7 thoughts on “Pressure Treated Posts: 1807.3.1

  1. Mike in Mississippi

    I have had this conversation with 5 lumberyards. We finally called the post manufacturer (national brand) and they can get .31 retention posts (actually they say they treat it twice and it works out to .28-.29), but they cost exactly double the .15 retention. Apparently the second time thru the chemical bath is really expensive!

    1. The story you are getting sounds highly questionable. First of all, it is beyond a stretch of my imagination to think a treater is going to treat material twice – there should be other orders with higher chemical retentions which the material you are after could be included with. Secondly – material treated to .15 is not going to be exactly .15, it is going to be .15 or greater, usually a fair amount greater as it is less expensive to use more chemical, than have to retreat. Third – the basic cost of the lumber itself did not change, just the amount of chemical, so if someone is suggesting the total price of the treated board is going to double someone is making extra profit off of it at your expense. I’d recommend you visit the Pro Desk at your local The Home Depot and see if you can get some straight answers there.

  2. Mike in Mississippi

    Agreed. I found it hard to believe. I called to speak with the wood preserving plant directly and was able to procure 0.8 CCA posts. I found Hansen Buildings site too late in the game as I have already had trusses built for my little goat barn. Having read all of the blog entries available over the past few weeks, it certainly seems worth it to contact the team at Hansen as there is an enormous amount of misinformation even among local “experts”. It would be worth it to have one source provide quality materials. Tracking down adequate materials has been a drain on my limited time and the quotes I received from local builders all included subpar materials. Upgrading wasn’t an option with most as they thought what they offered was good enough. I found the information provided on this website informative and I will now be face nailing my trusses at 12’ on center. I am having a hard time tracking down Machine graded lumber ( again, sounds like Hansen can package all of this and send it to your door). Will no. 2 common 2×6 purlins 2 ft on center with the crown up be sufficient to avoid sagging over time or would one need to go with 20”o.c.? I am going against convention for this area and many builders swear that no.2 2×6 purlins will definitely sag over time.

    1. Thank you for your kind words.

      Given your minimal possibility for snow, 2×6 #2 purlins of any of the four most common species of wood (SYP, SPF, HFir, DFir) spanning 12′ 24″ o.c. should show no perceptible sag.

  3. I’m replacing structural support beams in a 120 year old home and am researching to make sure I get the correct pressure treated lumber. While the beams will be sitting on concrete I’m going to get uc4b. Thanks for the information!

  4. A friend that works for a builder in pa said it is not code to bury pressure treated posts on concrete footings 30″ below grade. Is this true?

    1. 30″ may not be adequate for depth, however the balance would be incorrect – there is no code restrictions against embedded properly pressure preservative treated columns in the ground on a properly sized concrete footing.


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