Pole barn post backfill

I’m having a new garage built with pole barn style framing. What’s the “best” way to set the posts? I’d like to put them on piers…but pouring piers for 26 posts is a lot of work. The posts are about 3 feet in the ground. Can I pour a pad at the bottom of the hole, set the post, and back fill with dirt? Or should I back fill with gravel? Or does it matter?

I know a lot of people build pole barns, but I have always been told not to set wood into the ground. So, I would opt for piers to above ground level. A neighbor of mine when I lived in MO, used fiber board forms for piers that were about 12 or 14" in diameter. He dug down about 4' with a rental post hole digger on a little tractor (24" holes). Then he poured footers in the bottom. When they cured, he set up the cardboard pier forms, with 3 or 4 vertical rebars and string leveled the tops. Ready mix truck poured all of the piers in a few hours. When cured he filled with gravel to the tops of the piers. He did it all himself except for the ready mix truck(s). Two loads, footer and piers. His project was a massive porch 12' x at least 150' (all the way around 3 sides of his house.

If you set wood on footers and backfill the holes, I would use gravel as the back fill. Might help keep moisture away from the wood.

Codes can vary, but most require a footer(pad). Dig the hole, pour the pad, backfill around post with dirt, compact the backfill around the post as you fill it. The better you tamp it, the less likely post will move around. I put mine in 48 " deep plus footer depth. Usually a post will be reruiqed to be at least 48" into the ground.

My pole building was put up in the late spring this year. It is 50' wide x 40' deep x 14' high. The contractors used a hydraulic post hole digger to dig down 3 feet. They then put the posts in place, then poured in two 80 pound bags of dry concrete into each hole, and then topped the holes of with dirt. They then compacted the immediate area around the posts using their feet and body weight.

I don't know if this is the "correct" way, but they have been constructing pole buildings for about 15 years now. I had met with three other contractors and was about to choose one when a friend recommended this contractor, which I then chose above the others. I love my building, I feel they did an awesome job!


Chip

hamholfarm said:

My pole building was put up in the late spring this year. It is 50' wide x 40' deep x 14' high. The contractors used a hydraulic post hole digger to dig down 3 feet. They then put the posts in place, then poured in two 80 pound bags of dry concrete into each hole, and then topped the holes of with dirt. They then compacted the immediate area around the posts using their feet and body weight.



Chip

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Exactly how mine was done. I've heard arguments on both sides, encased in concrete or embedded in concrete. Here in the North East there are thousands of barns that have been built setting posts in the ground that are over 100 yrs old. They're still standing.

flesburg said:

If you set wood on footers and backfill the holes, I would use gravel as the back fill. Might help keep moisture away from the wood.

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Depending on soil conditions, gravel with a concrete pad at the bottom just creates a well for the water to sit in and rot the post.

Sonotube is the brand-name for the fiberboard forms. Auger the hole, drop the Sonotube in, and pour concrete into it to get it above grade. Sometimes overkill is a good thing!

Drill hole about a foot up on the post, pass a 1 foot long piece of rebar through the hole. Set post, dump in 2 bags of dry mix. It ain't going anywhere.

When my building was built, the builder drilled the holes, then set a premade concrete "pad" in the bottom, then back filled with crushed rock.
See my shop build pics link below. I think the building movie shows it.

Randy

PAToyota said:

Depending on soil conditions, gravel with a concrete pad at the bottom just creates a well for the water to sit in and rot the post.

Sonotube is the brand-name for the fiberboard forms. Auger the hole, drop the Sonotube in, and pour concrete into it to get it above grade. Sometimes overkill is a good thing!

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I agree with the first part of your reply. However, using a sonotube to get the post above ground defeats the purpose of post framing. The reason codes require the post to be buried in the ground is for shear strength. For example, picture a 6x6 treated post buried 48" in the ground, and back filled with compacted earth. The post will stand on its own, and could even take the stress of an average human leaning on it. Now, take that same post anchored to the top of a concrete plug created with a sonotube. Unless the post is attached with an anchor that has thick straps that travel up all sides of the post, it has very little holding it upright. It would have tremendous uplift advantages though if properly anchored to the concrete plug.

I have been building post framed building professionally on the west coast for 14 years. The proper way to set and backfill a post is as follows. Here in Wa state, depending on county codes, the hole has to be excavated to a depth of 48". A concrete footing 6" thick needs to be poured in the bottom of the hole. Dropping a sack of concrete in the bottom of the hole, setting the post on top, and then splitting the sack and adding water is also an accepted practice. After the post is in place, you can backfill with earth. I tamp as I go, and then use a small Bobcat excavator to drive around the post. This packs the earth well, but you do need to keep an eye on the post, and recheck plumb several times during and after. Also keep an eye on your post spacing as you go. Now, depending on the type of building, sometimes county codes require concrete backfill. In my area, any part of the structure that is not closed on any sides requires concrete backfill for wind uplift.

I hope this helps!!

You are correct, I did not go far enough with my explanation and omissions are errors in themselves. I'd anchor the post with something like this: http://www.strongtie.com/ftp/catalogs/c-2007/C-2007-p049.pdf

A lot of pole builders around here opt to use three 2x6's instead of a 6x6 for the fact that what they treat the lumber with will penetrate a 2 x better than it will penetrate a 6 x then they use either method to set the post. One will backfill with gravel for drainage, and another will set the post on concrete and backfill with dirt and tamp. It is divided about 50/50 on how it is done. Most of the time, if you don't have a real rainy season....three feet down is usually dry anyways, so if you have a solid base to set the post on you would be fine. Most would depend on your soils conditions of your area. An area with a lot of bedrock would be different than a place that has a lot of loam.

Kevin

hamholfarm said:

The contractors used a hydraulic post hole digger to dig down 3 feet. They then put the posts in place, then poured in two 80 pound bags of dry concrete into each hole, and then topped the holes of with dirt. They then compacted the immediate area around the posts using their feet and body weight.

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same here. And after hearing all my life that you should do otherwise, I'm leery, but I have read a lot of bits where they say not to embed posts in concrete, so I don't know.

Dirt here is about 3" topsoil, and then clay to the center of the world.

When I built mine, I dug the holes with a backhoe and set 80 pound bags of sack crete at the bottom of them. The post was then set on top of the bag and the holes back filled. It made for a good base for the poles to sit on

It doesn't matter if a post is backfilled with dirt or poured in concrete,it will rot at ground level eventually. I have changed thousands of power poles in the last 30 years,and every last one of em that was rotten,was rotten at ground level. When you pull the stump out of the ground,it looks brand new below ground. I've got some Thoroseal left over from my garage,and may try to use it on some posts next year when I build a carport. It may help,and it may not I'm 50, so I doubt I'll ever have to worry about it in my lifetime!