Pole Barn footing

[Riles]

I'm getting ready to put up a pole barn using pressure treated 4x6s set 4 feet into the ground. Is it better to use concrete or just backfill with gravel and dirt? The pressure treated timbers might outlast me, but at some point they will need to come out, and that job will be a lot easier without the concrete.

[BBK]

We have built several pole barns with locust posts and only used dirt to backfill the poles with. One if these is going on 35 years old with no signs of a problem.

[scsmith42]

Riles, one of the benefits of using concrete around pole barn posts is that it increases uplift resistance.   I've installed a number of tempory fence posts around the farm, and the smooth ones will slide right out after a few years (with a loader bucket pulling up), but the ones installed with concrete in the hole are a different story. 

I would consider using concrete under any of the following circumstances:

1 - you live in an area that frequently experiences high winds (such as a hurricane coastline).
2 - your barn is situated on the side of a hill, where passing winds may push "up" against the bottom of the roof.
3 - your barn will not be fully sided, thus there will be a lot of surface area underneath the roof to capture uplift.
4 - you have an enclosed barn but with large roof overhangs outside of the walls.
5 - you have a very tall barn (20' or higher), where the wind pushing against the upper walls may create uplift.

I haven't pulled this info out of a code book - just my personal thoughts.

Scott

[Raider Bill]

Scott is my hero! ;D

[Gary_C]

Yep, Scott is right as usual.  ;D

It is not just about holding the building up, you have to hold it down too.  :D

[PineNut]

On the last poles I installed, I nailed treated lumber around the bottom of the pole. This should increase the pullout resistance. Of course it depends on how well the nails hold up under ground as to the life of this method.

[Riles]

I'm on the west side of Charlotte, the last hurricane was Hugo. The site is pretty well sheltered, the only item on your list that makes me think twice is the lack of walls.

When they dropped off the timbers yesterday, I noticed I didn't even get the green stuff, looks like I got the "Yella wood" treated stuff. I wasn't even sure it was pressure treated until I read the label. Now I'm leaning away from the concrete because I may just outlast the wood.

[moosehunter]

I was told by a fence builder to not use concrete as it would hold moisture in the wood and cause it to rot faster.

[Engineer]

Skip the concrete, use a mix of crushed stone and stone dust, tamp it good. 

If you nail a few blocks to the buried ends of the posts with some stainless nails, it will help with the uplift.

[Onthesauk]

They used sand to backfill for my polebarn.  Same explanation, the concrete holds water.

[PineNut]

I have noted two uses of concrete on posts in this area. When there is a heavy vertical load, a bag of cement mix, still in the bag, is placed in the bottom of the hole. This is to provide a larger footprint for the post. When the post has a side load on it, sometimes a collar of concrete is placed around the post near the surface of the ground. I have not observed it but should be much better if washed gravel was placed under and around the lower part of the post below the concrete.

[gharlan]

I think you would be wise to look into the Yella wood before use. I do not think it is treated for ground contact. They still make the ground contact stuff but you may have to frequent a full lumber yard to find it as the big box stores only carry a limited selection.

[Ed_K]

 I poured concrete 4' with galvanized angle iron sticking out and bolted the 6x6s to that. I used hemlock with the thought that if one fails I can remove and replace it. They've been there 23 yrs and only have a few splits running with the grain.

[Handy Andy]

  Ed, that sounds like a good idea, use poles but bolt them to the footing.  Question,  what size angle iron did you use.  I have seen Morton buildings repaired that way when the poles rotted off, they just put a strap iron on each side of the pole, then filled the hole with concrete.

[okie]

I just got "Practical Pole Construction" by Leigh Seddon from the library and in it the author says to place 4 lag screws around the bottom of the post and set the post in the ground and pour a 12 inch "concrete neclace" around the post and then backfill with tamped gravel, this resists uplift, uses less concrete than total enbedment, and by leaving the bottom of the post uncovered by concrete allows the post to remain "dry" as there is nowhere to hold water.

[scsmith42]

Okie, one other benefit to Seddon's recommendation is that you have more uplift resistance by having a concrete "collar" at the bottom of the hole versus total encasement.  Uplift resistance is determined by a "cone" of soil above the concrete.  If you totall fill your hole with concrete, you actually have less uplift resistance than by placing a collar at the bottom.

That's one reason why a lot of communication towers have "pad and pier" foundations instead of simply large pads.

Scott