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QUESTION: Hi Stephen,

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.

I live in PA and this is a detached garage.

Thanks

Mike

laminated post
laminated post  
ANSWER: Mike,

I would avoid plastic or tar coatings, because they can trap water and accelerate rotting.  Surrounding the post in concrete will end up cracking the concrete, making the technique pretty useless.  

It is best to surround the posts with clean gravel (like #1 or similar), especially at the lower 1/2 to 2/3 section underground.  You want to keep water from sitting against the wood for prolonged periods.  Don't fill with gravel to the top, however, as frost tends to flow quickly through gravel.  Much of these design decisions depend on your exact soil conditions.  For example, a well drained sandy soil will be drier than a heavy silty-clay.

Some barn companies, like Morton, use a laminated post of three 2x6's.  The treatment chemicals tend to fully penetrate these smaller wood sections. Plus they can be easier to work with, as the post can be installed in two parts.  I think you can see this from the attached picture, which shows the triple-2x6 treated wood post (which is set first) and the interlocking non-treated top section (which is added after treated stubby posts are set and grading is done).

Best of luck and let me know if you have additional questions.

--Steve Major

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

PermaColumn Pic
PermaColumn Pic  
QUESTION: Hi Steve,

Thank you for sharing great ideas for success with poles in the ground.I followed your tip looking at the Morton website. I like how they have only the underground portion of the pole pressure treated and then have "finger joints" above ground with regular wood attached.

I also noticed on their Morton website they use 6x6 concrete posts in the ground then above the ground they attach regular 6x6 wood to the roof-line.

A local company uses a similar concrete concept called perma-Column. I am attaching a photo.

What are your thoughts on going this round verses pressure treated wood underground of benefits verses cost?

Many Thanks Steve!

Appreciatively

Mike

Answer
Mike,

The perma-column (or some variation of it) does a perfect job of protecting the wood from decay.  Just realize that by interrupting the continuous post with a somewhat weak joint, you lose some "tip-over" strength in the post.  A continuous post set 42" or more in the ground helps considerably to resist wall racking.  Just be sure to use proper wall bracing to account for this, either solid sheathing (like plywood or OSB) or steel X-bracing.

The perma-column involves more labor and care must be taken to position them perfectly.

If I was building this myself I would use the Morton fingered post system.

Best,
Steve

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Stephen Major

Expertise

I can answer questions in the following categories: architectural design, architectural woodwork, structural design, building construction, kitchen and bath design. PLEASE indicate your state or region, so I can provide the best possible answer. PLEASE provide photos whenever possible.

Experience

30 years in the building design and construction field, with emphasis on residential and light commercial projects. This includes over 10 years performing property condition assessments on commercial and industrial properties.

Publications
Author of "Architectural Woodwork - Details for Construction" published by Van Nostrand Reinhold (now Wiley).

Education/Credentials
BS Cornell University.

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