Pole construction... my dilmena with concrete piers vs. in ground

[EddieWalker]

I've used pressure treated 4"x4" posts for structures in two completely differing environments on my property. One where the soil is dry 100% of the time and these posts are still in perfect condition. The other - the soil is damp to water saturated 100% of the time. Here the post last around 15 years before they rot off at the ground level.

My suggestion - keep the wood out of the ground. Use concrete in the ground - wood out of the ground.

Did you use ground contact 4x4's in the saturated soil instead of dock posts? What was the reason for the posts in the saturated soil?

 

[upstatefarm]

Thanks for all the good ideas. I drained the holes yesterday, and today there's about 8" of standing water. This is an unusually wet summer, but I can see anything other than maybe a utility pole rotting out pretty quickly. So I'm going to go with piers, and use square foots for additional uplift bracing... a little more $ but I think it's worth it. Thanks for the help!

 

[quicksandfarmer]

That also looks like a good idea for existing posts that have rotted off at ground level, but have a floor slab poured around them.
Cut the rotted post flush with floor, slide post bracket assembly under, drill expansion bolt holes in floor, install expansion bolts, and put lags into sides of post.
My Morton is now 34 years old, and the posts still seem good, but just underground, they may not be as good as I think they are.

Getting a little off-topic, but I did almost this exact repair in my pole barn, which has a poured concrete floor and had one post that had rotted at ground level. First I used a jack to jack the post up, and I cut it off at the edge of the rot, which was about six inches off the floor. Then I removed the rotted wood, which left a post-shaped hole in the floor. I bolted a post cap to the wood that remained, and scabbed 2x6's to the post to make a form, and filled the hole with concrete. When the concrete hardened I removed the forms and the jack. It has held ever since.

 

[Egon]

There are bell shaped forms for just what you are proposing to do. Concrete can be poured with water in the hole.
[video]https://www.google.ca/search?q=bell+shaped+pier+forms&ie=UTF-8&oe=UTF-8&hl=en-ca&client=safari[/video]

When you backfill add a little Masonary lime to the backfill. That will make for a harder backfill.

 

[muddstopper]

I will just throw this out there for thought. If the op is concerned about weight using 6x6, you can buy 4x6pt for post. even tho some PT lumber is rated for ground contact, it will still rot over time. I agree with molst everybody else, concrete in the ground, wood above ground.

It been several years since I had to rasie a barn and place new footers under the post. barn was built in the 40's and post oak was used for the post. Over the years, the post slowly rotted away in the ground and the bard was sagging pretty bad. I took jacks and attacked to each post and slowy jacked the barn back to a visual (eyeball) level state. Then sawed off the rot at the bottom of each post and used railroad ties as footers, digging them into the ground and then setting the post back down on the timbers. I forget how I fastened the poles to the timbers. I do know it was a scary job and I had to start on one side and work my way around each wall, going a little at a time. The barn out lasted the owner, but it eventually collasped during a big storm.

After raising the barn, the old house had similar sagging problems. Originally built early 1940's. It was a cinder block house, built using saw mill lumber. The concrete blocks just had holes knocked in the sides and the floor joist inserted in the holes to support the floor. Of course after 40 years, the end of the joist where it contacted the concrete blocks, was rotted away and dropping down. To fix this, I made a band to go all the way around the inside the blocks and under the joist. I had to do this to the outside walls, as well as the center. Again, I pulled out the jack and worked my way around the entire house, going a little at a time, jacking everything to a level height. I installed the new band by pouring a concrete pad and used 6x6 post to support the band. I then scabbed new pt floor joist to the old joist, supporting the new joist on each end with the new band. I can say, it was a lot of dirty and hard work working in the crawl space on a red clay soil, but the owner is 82 and I suspect the fix will out last her.. Anyways, keep the wood off the dirt, do it right the first time and it will last a very long time

 

[jimmysisson]

A sonotube lowered into a wet hole turns to mush right away. I hate the things. We pour a footer in each hole; that gives you leeway to move the posts to align them - makes all else easier. Than place your pt 6x6s and brace them plumb. Backfill with previous material.
Jim

 

[jimmysisson]

Also, once you're built, drill a 3/8" hole just above the floor into each post at a downward angle. Every few months fill each hole with diesel or used motor oil. It will saturate the wood fibers just below grade and the posts will last and last.
Jim

 

[GLyford]

I built a porch using the plastic footing forms (bigfoot, squarefoot) that you screw a sonotube onto. That might be enough to get your tubes out of the standing water, and it would give you more support. I wired an "x" of rebar in the bottom, with a straight stick coming up through the tube too. Held in place up off the dirt and centered with bits of tie wire through small holes in the plastic and tube forms.

Shop Bigfoot Systems 19-in Concrete Footing Form (Common: 25.5-in; Actual: 25.5-in) at Lowes.com

SQUARE FOOT 22 in. x 16-1/2 in. x 22 in. Plastic Concrete Footing Form-SF22 - The Home Depot

 

[quicksandfarmer]

Around here the standard is 30 pounds per square foot for snow load, 10 psf for dead roof load. Without testing, soil is assumed to be able to hold 1000 psf. So you need one square foot of footings for every 25 square feet of roof. If the addition is 16x24, I'm assuming the posts are on 8' centers, so there is 64 sf of roof for each post. So each post needs 2.5 SF of footing, which is a square 20" on a side or a circle 22" in diameter. A 6x6 post is 0.21 sf and not nearly enough bearing surface.

As Jimmy noted, the alternative is to trench a footing. Minimum width for a footing is 10", which can support a roof up to 41 feet wide.

 

[upstatefarm]

Thanks for all the ideas. The ground has dried out a bit more and the ground water level dropped, so I poured the piers yesterday: 8" of gravel which got me above the ground water (for now), 28" round Bigfoots (bell shaped plastic forms like square foots, as a footer) from HD, 12" sonotube, 4 vertical rebars in each pier. And an anchor bolt in the top of each pier, for a post base bracket. Now, with the piers, the post height isn't too bad, about 10', so weight is less of an issue now, so I am in fact considering 6x6's... yet there seem to be a lot of people who have had twisting and warping problems after they dry... which I really don't want to deal with down the road. That's why making laminated posts seems to make so much sense, even if it is a little more work... two 2x6 with 1/2" plywood glued and screwed in between, and carriage bolts every 4'... that seems to be the consensus of the best way to do it. Thanks everyone!