wood post burial

[NM_Dan]

Hello,

I have been visiting this site for some time now and I have found it very helpful.  I am getting ready to start a project at my ranch property and I am looking for some help.  I am going to build a 20 x 28 shade structure and was thinking of using 8x8 pressure treated uprights or possibly pine vigas treated at the bottoms and the holes filled with concrete. It will have wood trusses and metal roofing. I would like to hear all thoughts and ideas on burying posts like this.  Thanks Daniel

[rocking23nf]

Ive never seen an 8x8 post, is this something custom made?  Thats gonna be one heavy post!

[John Raabe]

I would advise that the concrete be used as a collar in the base of the post and then use well draining material such a gravel within 8-12" of the surface. This will perhaps double the life of the post.

For an open structure you will want to cross brace the posts and beams and have clips to hold the roof on. This will provide wind and racking resistance.

[JRR]

In my neck of the woods ... hot, wet, and home for the termite nation ... I would always advise separating wood and earth several inches, especially for wood that gets some rain.  The concrete could be poured directly into forms, such as Sonotubes, to make short pedestals/piers/footings.   The footings would include reinforcement and steel anchors for attaching the columns ... and be massive enough to provide some uplift resistance.  The tops would be shaped for good drainage.

Of course, your country may be dry and free of bugs.

[Don_P]

Post Frame structures, pole barns, etc, often get much of their racking resistance from treated posts buried 4-6 feet deep or more. When you look at those structures and want to build something without a fully embedded post that racking resitance needs to be built in a different way as John mentioned, knee braces or cross bracing.

[MountainDon]

  NM_Dan.  The NM is for New Mexico?  NM_Shooter and I call this place home.  

You will find two basic schools of thought on whether or not to use concrete to set pressure treated posts. Some say yes absolutely and others say no way.    Nobody has any concrete proof that I have seen. None of the PT manufacturers information that I've seen says it's a good thing or a bad idea. Some codes might have specific requirements. In those cases code must apply.

Water will accelerate the deterioration (rot) of the wood at or near the ground surface. I believe it is best to not encase the PT post in concrete. The post hole should be filled with material that will provide lateral support as needed and drainage. The ground should be built up around each post to assist in draining water away from the posts. A concrete footing/pad may be necessary to provide support by spreading out the post load over a larger footprint than that provided by the post end.

Part of my reasoning on this comes rom experiences with non treated wood posts. In those cases I can recall having to replace many concrete encased posts that had rotted near the ground/air interface. I figure if the concrete encasement made it bad for those posts maybe it doesn't make sense to possibly aggravate things even if the wood is PT. It will last longer than non treated wood, but it is not totally immune.

I also base my opinion on my experience a dozen posts I have in my backyard. We have a playground structure that is about 19 years old now. The posts are PT. They have a ring of concrete around the post base about three feet in the ground. The holes were all filled with the mix of dirt and sand that was dug out. There is no rot in evidence at all. The structure is solid. As well the termites have bypassed the posts.

[Don_P]

If you're really looking for late night reading,
http://bse.wisc.edu/bohnhoff/Publications/Copyrighted/EP486_1.pdf

[NM_Dan]

Thank you everybody for your input.  The info provided will help when it comes time to get this project started.  I am planning on cross bracing the posts and using clips for the roof. 

The NM is for New Mexico, born and raised in Albuquerque north valley.  Mountain Don, I have looked at your post on your Jemez cabin and you have done a great job.  The Jemez area is such a beautiful place, I love to take the family fishing there.  Nice to see a couple guys from my neck of woods in this forum. 

[MountainDon]

NM_Dan, do you need any firewood?
Free for the taking.
I need people to take some.
Free.
Some already cut into 4 foot lengths.
Did I say free for pickup?