Depth of Pole Barn Posts?

[Beltzington]

After a considerable amount of research, I believe I'm going with buried posts instead of cement piers. What I can't seem to get a bead on is how deep to set the posts. I have read 1/2 their heights, 1/3 of their height, 4-foot is more than enough. Since there is no frost-line in my area, I am only concerned with the minimum depth for a secure structure. Aprox details are:
Barn 16'W by 36'L
6" by 6" poles need to reach 16' above grade and will be set on 8' centers.
Idea is to build the center part of the barn first and add the side shed roofs later. Another TNB member built very similar project years ago but it seems he has left. Attached is PualT's barn that shows what I have in mind except I plan on extending the posts all the way to the roof.

 

[sal64]

my pole barn i buried the poles 4ft deep on a small concreet slad that was coed in my area. u should put a flat rock at bottom of post so post dosnt sink.

 

[DennisArrow]

For me, with a 16' above grade height, I would go 4' deep........A 2' diameter hole......Creosote, treat the below grade of the posts.........Set the posts on a bed of large rock/gravel.........Fill the hole up with concrete to just above grade and taper that down to grade, perhaps an inch high..............

Make sure you have some strings run and or a laser to check that the posts are plumb and in line with one another and YOU have it...........

Sounds like you are on the right road.........Good luck......Dennis

 

[Mickey_Fx]

Think depth will vary with soil conditions. If memory serves me right, I recall we dug 4' deep holes and put a ft of pea gravel in the bottom and set the post on top that. Filled the rest of the hole up to ~1ft level with gravel as well. Didn't fill the holes up very far until we had the posts positioned and vert. Once postion was final, then finished filling the holes.

Barn has been up for >30 yrs and doesn't appear that any of the posts have moved.

 

[winston1]

I've build several bldgs. similar to your pictures Between 2 and 3 ft is plenty deep. Have drilled holes and slipped re-bar thru same length as hole diameter to hold post from going down. Your siding, roofing, etc is what gives you strength. Most treated 4 x 4s or 6 x 6s would warp to high heaven if not tied and braced together with structure. I'm sure this will be jumped on but that's OK. This is my opinion based on experience. I am talking about cementing the posts in the ground.

 

[carpenter383]

I've build several bldgs. similar to your pictures Between 2 and 3 ft is plenty deep. Have drilled holes and slipped re-bar thru same length as hole diameter to hold post from going down. Your siding, roofing, etc is what gives you strength. Most treated 4 x 4s or 6 x 6s would warp to high heaven if not tied and braced together with structure. I'm sure this will be jumped on but that's OK. This is my opinion based on experience. I am talking about cementing the posts in the ground.

I agree 2-3ft deep with concrete around the post should be plenty (2ft if it's not too sandy or any chance of water wash out) Think about how much force it would take to move a post sideways that's 2ft in the ground. (while keeping it level) The roof and siding should take the racking forces, not the depth of the post.
They sell pre built sheds, small cabins, mobile homes, etc that are free standing with no posts/foundation. The bottom of the walls get their strength from the floor.

 

[timswi]

4ft on mine with a concrete base...Packed the original dirt above that.

 

[whistlepig]

4' deep with a concrete pad at the bottom. That was building code where we lived before. I had another barn built when we moved here by the same builder (Blitz). They did it the same way. 4' deep with a concrete pad at the bottom.

 

[keegs]

After a considerable amount of research, I believe I'm going with buried posts instead of cement piers. What I can't seem to get a bead on is how deep to set the posts. I have read 1/2 their heights, 1/3 of their height, 4-foot is more than enough. Since there is no frost-line in my area, I am only concerned with the minimum depth for a secure structure. Aprox details are:
Barn 16'W by 36'L
6" by 6" poles need to reach 16' above grade and will be set on 8' centers.
Idea is to build the center part of the barn first and add the side shed roofs later. Another TNB member built very similar project years ago but it seems he has left. Attached is PualT's barn that shows what I have in mind except I plan on extending the posts all the way to the roof.

That's one handsome pole barn Beltz...

If we get past this recession without too much damage, I'm going to have one built just like. If you don't mind me asking, is that a second floor hay loft?

 

[rgood]

4 feet

 

[MarkV]

Well the right answer is whatever your local building department wants. Give them a call, they will tell you. Here is like others have said, 4' deep x 16" hole with a 6" concrete bottom. Backfilling with concrete, gravel, stone dust or native soil is a much debated issue. Some swear by concrete and others feel it traps moister nest to the wood.

As a side note, in your other tread you mentioned building a living space on the second floor of the barn. That is the one thing I would not be too vocal about with the code people. All depends on your local regulations but in many areas they don't allow that unless the whole building is brought up to same level of code that a house would be.

MarkV

 

[Mike120]

It depends on where you are and your ground conditions. To get the right answer you need to do a soil boring. Here, I've got sandy loam (and a high water table) with a clay layer at around four feet. The sandy loam is great for crops but won't support anything. I had to go down five feet to get to anything solid. I also had to build a 36" pad (24" under the barn) to put under the slab so it would be supported. Because I'm in the gulf coast area I also had to design for high wind loads.

Even though I'm a Civil Engineer, I still had to get a third party to do the soil boring and stamp the foundation design for my house to get a structural waranty. The boring was close enough for me to use for the barn and other buildings and I've had no problems with getting building permits and everything insured under my farm policy. Being a typical engineer, I probably over-engineered everything, but I have a lot invested and don't want any questions if I ever have to make a claim. As I recall, the soil boring was less than $150, but now I know exactly what I'm dealing with and can plan appropriately.

 

[catfishdaddyengineering]

Great looking barn! I have plans that call for the same under roof (16ft) and they call for 20ft poles with 4ft in the ground. My plans when built will look just like yours, just a little bigger: 44W (20ft center plus 12ft sheds) x 40L.

 

[Stimw]

I when 4' to give the hurricanes something to tug on!
I coat everything in the ground with used motor oil, even PT wood. I put it on with a paint brush and allow to soak in and if it soaks in too much I retreat before planting.