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Architecture/30 Years ...Pressure Treated Garage Poles


QUESTION: Hi Richard,

I plan to build a 28 x 28 pole building garage. Online I read horror stories about the pressure treated lumber rotting underground and the headache associated with replacing them by removing concrete flooring etc from around the rotted pole.

Now that pressure treated lumber is copper based rather than arsenic based, how much faster will the part of the poles underground rot?

In talking with builders I hear various ideas about how to put the poles in the ground. One plan puts the pole in the ground on a concrete footer but have the underground portion of pole encased in steel to keep the water and soil away from the pole. How effective is this idea?

Another plan encases the underground portion of the pole in concrete. I have seen water penetrate concrete grease pits in a garage. How effective is this plan of encapsulating the pole in concrete to slow down rot?

A third builder said he heard of “hot dipped” poles, but he did not know what they are dipped with. Have you heard of this "hot dipped" method?

How well will tar or roofing cement stick to pressure treated lumber? Thoughts on whether how well tar or roofing cement will help or hurt the wood?

Any input you can share on these ideas or alternative ideas you have to share that will better preserve the poles underground would be greatly appreciated.




That is a fairly big shed that you are planning to build.  I would recommend that your poles consist of three-ply 2 x 8 that are 0.6 ACQ treated (suitable for contact with ground).  I will see if I can send you a typical detail that is used fairly often.  The detail illustrates a 48" deep hole 18 inches in diameter with an 18" dia. x 6" thick concrete "cookie" dropped into the bottom of the hole.  It is important to have a 2 x 6 x 12 uplift block fastened to the bottom of the pole to resist uplift from high winds.  These uplift blocks are fastened to each side of the post bottom with four 16d galvanized ring shank nails.  Perhaps these details do not answer your question about durability but I need to be sure that you do not make the most common mistakes when building a pole-framed building.

As for increasing the longevity of the poles, I believe that you can expect that these will last 30 years regardless of what you do to make them last longer.  The rate of decay will depend on the number of wet and dry cycles.  Every time the wood absorbs moisture and then dries out again is a dry cycle.  If you can submerge your building in water, then it will last a long time.  If you can keep your foundation from every getting wet, then it will last a long time.  The problem with applying a creosote coating (commonly used on telephone poles) is that it works both ways.  If water somehow penetrates the pole, then the protective coating only slows down the amount of time necessary for the pole to dry out.  Considering that creosote is so common, then I would assume that it might be worth it.  Filling the hole around the post base can be either concrete or gravel depending on your pole spacing, knee bracing, and any other diagonal bracing.  I would recommend gravel to ensure that water drains away from the pole base which will help keep the pole dry.  Concrete soaks up and retains water but will ensure that the post base is ultra stiff and the pole cantilevers out of the ground.  This cantilever negates the need for additional lateral bracing.

All other wood not in contact with the soil or below grade may be 0.4 ACQ treated.

I hope that helps.

Send me an e-mail and I will send you the typical detail.

Richard Burton, AIA
Registered Architect
ICC Certified Plan Reviewer
NFPA Certified Fire Plan Examiner

---------- FOLLOW-UP ----------

QUESTION: Hi Richard,

In the first sentence of the second paragraph of your reply above, you stated, "As for increasing the longevity of the poles, I believe that you can expect that these will last 30 years regardless of what you do to make them last longer."

Since arsenic was removed from pressure treated wood and a switch to copper was made in 2006, how does one estimate that the newer copper based treatment will last 30 years as a post for a pole building in the ground?

Hope you have a delightful day!




Just yesterday, I learned that the ACQ treated lumber (that replaced CCA treated lumber) is being replaced with MCa and MCQ treated lumber (Micronized Copper).  As you know, the ACQ (Alkaline Copper Quartenary) was deemed to be too corrosive to galvanized and aluminum fasteners.  Stainless steel fasteners work well but who can afford it?

Meanwhile, it is up to the USDA Forest Products Laboratory to test the new MCa and MCQ treated poles in the same way they tested the CCA and ACQ treated poles.  They simply bury the poles in a few select areas of the country to include the harshest coastal environment.  After 30 years, they perform a simple test to determine if these poles pass or fail.  If there is a more scientific way to "guess" how long these poles will last without waiting 30 years, then I have not become aware of such a test.

I hope that helps.

Richard Burton, AIA
Registered Architect
ICC Certified Plan Reviewer
NFPA Certified Fire Plan Examiner


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Richard Burton AIA


A combined total of 25 years experience with construction, architecture, and building code enforcement. Ask me about residential and commercial design. Ask me about design aesthetics, structural methods, and building something that will withstand severe weather conditions. Ask me my opinion about YOUR design ideas and I will tell you the merits of good design and challenge your thinking about practical issues. Ask me how to best find and work with your local architect and approach general contractors to get the most value for the least amount of headaches. You can ask me about improving your energy efficiency and things that are both green and practical. But don't ask me about solar panels and wind turbines unless you are currently paying your utility company 35 cents per Kilowatt. Otherwise the math does not justify the initial cost and return on investment. Ask me any building code question and how to get a building permit from the most difficult enforcement agencies.


Here in the midwest, we design and build "green" in ways that make sense. My construction methods prioritize weather resistance, ease of maintenance and durability. While a graduate student in San Diego, I taught drafting and history of architecture. After working ten years for other architecture firms, I have started my firm Arrow Architecture in 2008. More than half of my work involves commercial office buildings. But my portfolio of work also includes custom homes, residential additions, home remodels, and second story additions.

President-Elect of American Institute of Architects - Lincoln, NE

B.S. Architecture - (Interior Design) University of Nebraska Lincoln 1997 Master of Architecture - (Urban Design and Professional Practice) NewSchool of Architecture - San Diego 2004 Graduated Summa Cum Laude ICC Certified Building Plans Examiner

Awards and Honors
AIA Henry Adams Medal and Certificate

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