Anyone build barns? bigger pole barn in shallower soil?

[Macintosh]

Anyone here build pole barns? Would love to get some advice.

we are seriously considering building a reasonably good-sized pole barn for a tractor and some other similar stuff, probably somethinglike 18x26+ and with a few feet above in order to raise roofline for a shed roof on each side and provide a big useable storage loft. We’ve shyed away from a stick built construction for cost of the foundation. We would do pretty much everything ourselves. The only site we have is currently forested, and has soil varying between 6” and 2’ deep on top of bedrock. I am worried about not having enough consistent depth for the posts, I know the bedrock wont heave with frost really, but my impression was the depth also provided some stability. Everything I have read so far says to sink posts below frost line, which around here is deeper than 3’. If Im only able to get, say 18” or less on many of the posts, is a pole construction questionable or a no-go entirely, or are there ways around this, etc? I could see drilling some rebar into bedrock and pouring sonotubes on that, and attaching posts to that with a metal wet-set fixture, but not sure how realistic or necessary that is.
what say the experts...is shallow soil like this a no-go, or does it work for the size construction we are talking about?
thanks in advance

 

[elkguide]

By only going 18", what is going to hold your posts in place?
Going high enough to be able to put sheds on each side would require you to go up to say 16 feet for a 12 foot shed with an 8 foot height on the side opening, in my experience would require you to go at least 3 feet in the ground and preferably 4 feet. The last pole barn that I built had 12' plates and we went 4' deep with the posts.

 

[Macintosh]

Thats exactly my question. Is doing something poured onto the bedrock (or something else?) going to make up for that, or no? I dont know how to tell.

 

[def90]

This is what a building engineer is for.

With bedrock that shallow you should be able to pour a foundation or variation of concrete pier/slab right on the bedrock and then go from there with either post and beam or stick framing.

But as mentioned this should all be run by a building engineer.

 

[Macintosh]

It will not be run by a building engineer, I know thats the right answer but it aint happenin for a pole barn. Also there is no code here for a building like this. Pouring a slab will more than triple the cost of the project, so if thats the only way, we simply arent going to do it.

 

[dieselchessy]

The poles sank in the ground are what provide the wind shear for the building. Pole buildings aren’t framed and sheathed to provide the lateral stability like stick framed are.
I’m pretty sure if you can’t sink the poles 4 or 5 feet in good soil, a standard pole building would be out of consideration.

Pole buildings are engineered by the way. At least where I live and it’s required.

If you run shallow poles the building would need framed and sheathed in a way to provide the lateral stability. The front would have to have some width to the walls and couldn’t be all door.

 

[YellCoAR]

Why don't you just pour cement square footings and anchor the poles or 4x6 post to them?

 

[Macintosh]

Thats more or less what I was suggesting with the sonotubes/rebar just for solid footing on very uneven bedrock. But if a square footing is more stable thats easy. We’d pour the base, and then use blocks and concrete or a poured tube to get above grade, and anchor 6x6 (or whatever) posts to that with a wet set bracket. Thats more or less how we built my house growing up. But that's sided per the post above—intention is to eventually side this, but still different.

 

[Pony Soldier]

I built a 40 x60 over 15 years. It's 19 ft at the peak. My holes are down about 3 ft as that is where bedrock starts. Part of the soil strength starts with the type of soil. We have a high clay content and digging is hard. If you have light topsoil, you are likely out of luck. Another is what is the bedrock. We have an altered granite that you can cut your way through by hand over a few days or with a backhoe.

Then you are down to compressability of the soil. Mine was wet in the spring but like concrete after July. I tamped mine back in but otherwise would have had to backfill with cement. I built it on ten ft spacing and would suggest at least 12 ft at least in the center. That spacing came from 2x12 rafters in 20 ft lengths. These are doubled up on both sides of the 6x6 uprights. The roof supports are 2x6 uprights on 2ft center between them.

I started with a 20 x 40 three sided building that half was for hay and the other half has a shop in the bottom and storage upstairs. I measured out my posts and built a 20 x 20 twenty ft away. Over years I accululated pieces as I could afford and built the second 20x20 and sheeted that third. Finally I filled the middle in. Again with the same rafter assembly. Trusses required more capital and equipment to set them that I didn't have. I think my total cost was between 5 and $6,000.

On a place like you describe, I would rent or borrow a backhoe / excavator and probe for soil conditions and depth for your locations. You need to raise the floor up 18 inches anyway to control water flow unless your are happy with mud.

Find out what your snowload will be if you have snow and design accordingly. Visit your neighbors if they have polebarns and find what worked and what didn't and design accordingly.

Internal structures (2nd floors) on the windward sides with a number of cross bracing will increase strength. Break things up into triangles internally for both lateral and rotational strength. And lastly build for the worst possible conditions strength wise. It's cheaper than building over.

Design for the conditions you have or could get. Visit a number of them for ideas and don't cheap yourself to death.

 

[Macintosh]

Thanks, appreciate that very much Pony Soldier.

 

[Blockcaver]

Drill holes a foot or more in the bedrock, grout (epoxy or even cement) heavy rebar (#7) into the rock holes and have the rebar extend up to within 2" of the top of concrete to pour in the Sono tubes. Pour the Sono tubes up to a few inches above final grade for your assumed gravel floor in the pole barn.

Cast into the top of the concrete tubes whatever anchor system you plan to use to secure your poles to the concrete. We used a cut piece of wide-flange steel beam cut to length with the top flange cut off and with anchors (L-shaped rebar) welded to the bottom that were cast into the concrete. We slotted the square poles (6"x6" and 8"x8") on the bottom end and bolted them to the pre-drilled anchor plates with 3/4" diameter all-thread (8" posts) or bolts (6" posts).

Message me with a number to text to if you want photos.

 

[AKBC]

Is the rock really so competent that you cant drill into it a foot or two with a bobcat or other style drill? Or maybe a jack hammer? It has been my experience that usually the surface of bedrock is weathered.

 

[Macintosh]

I can absolutely drill into it. It's buried and quite uneven where it is exposed, but it is pretty compact schist. It's actually very hard stuff, but have drilled plenty of 1/2" by 4 or 5" holes in it with a bosch hammer drill in other locations. No reason the same thing in a rebar-sized hole and glued in with sika or similar wouldnt work fine.

 

[Blockcaver]

If the rock is well weathered, it should drill with a large auger drill used for the post hole or can be ripped out with a backhoe, which makes a very large hole that needs back fill that is well compacted. If not weathered, drill it with an electric hammer drill or pneumatic breaker/drill.

 

[Macintosh]

Yeah, it's nowhere near that weathered where i've had to work with it. it's not granite, but if you think of granite like a solid mass of stone, that's more like what I'm working with. a good 1/2" bolt in that stuff will hold tens of thousands of pounds.

 

[Blockcaver]

Just get it anchored to the rock with 4 rebar per footer and you’ll be good. Good luck!

 

[Dirtscoots]

My shop was engineered and every 12 foot bay they angered a 7 foot hole then poured a foot of concrete for the post to sit on then roughed in all the poles and filled the holes with concrete to ground level. I have 18’ eaves.