Hello All, I am having a 20x50x12 Pole Barn built. It will be used as storage/ workshop and size is due to set back and location. I have to handle the site prep work, im going to have 4" of gravel 2" foam and 4" concrete. With that said i figured 3" of concrete sticking out at the highest point for drainage purposes so i would only cut down 7" from the hightest corner( Didnt realise this till it was too late). So i dont do site work usually and i think i messed up, i began cutting the soil down for 24x54 so there 2' working space on each side but i used the driveway as my reference for grade which is about 15' away from the front of the pole barn. So ultimately i cut my site about a foot deeper than i should of, instead of being 7" below the highest point, i am about 19" so the question is, should i just put the dirt back and compact it with my small kubota tractor or do i need to get crushed stone and compact it to make that foot up? And unfortunately the builder is supposed to start building the 26th of February and the permits were approved yesterday so i didnt want to start till they were approved. Any help in this topic would be amazing!
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Pole Barn Site Prep
- Thread starter sympler
- Start date
- Replies 10
- Views 579
I would use crushed rock packed with a vibe roller between lifts of a few inches.
I made mistakes like this when I first built. It seems easier than it is.
You need a vapor barrier under the foam. Don't forget that. And rear.
And don't pour your slab with 4" edges. Make the edges a foot or so thick atleast. Otherwise all the critters will burrow under the slab.
I made mistakes like this when I first built. It seems easier than it is.
You need a vapor barrier under the foam. Don't forget that. And rear.
And don't pour your slab with 4" edges. Make the edges a foot or so thick atleast. Otherwise all the critters will burrow under the slab.
I just built a pole building this past october. First time doing it and did basically the same thing. I came back in with crushed stone and every 2 inches we compacted it with a vibratory roller. I was only 6 inches off so it wasn't to bad. The last layer I wet down a little compacted and then it sat for about 2 weeks and came back and compacted it again to be sure. I put 4" gravel vapor barrier then 5" of concrete. No problems this far and i have ran equipment inside the building and also put a 6 ton lathe in the building.
I’ve broken through 4” slab with a outrigger on a crane truck, went through like a hilti nail.
6” is the min to me with RC40 concrete , fibre crack inhibited , controll cuts at whatever your local code is.
There is a dpc membrane under your concrete, PU insulation 2” of blinding sand under that and in some localities another membrane for radon ( houses normally)
The hardcore should be layered, about 3” then compact, rinse and repeat.
It’s a mistake ( I’ve made it) to try to compact any more than 3-4” with a compactor, you’d need a big vibrating roller for thicker , can’t remember the joules of the roller but it’s orders of magnitude grater than a compactor plate type.
Good foundations make good buildings, id consider getting a reputable concrete contractor, easier on your back, big concrete slabs are bloody hard work ! You want young fit guys to handle the stuff, a 3’ pad will bugger me up these days, no more lines of concrete wagons thanks, and a pro with a bull float or a powerscreed makes it look easy.
Mark
6” is the min to me with RC40 concrete , fibre crack inhibited , controll cuts at whatever your local code is.
There is a dpc membrane under your concrete, PU insulation 2” of blinding sand under that and in some localities another membrane for radon ( houses normally)
The hardcore should be layered, about 3” then compact, rinse and repeat.
It’s a mistake ( I’ve made it) to try to compact any more than 3-4” with a compactor, you’d need a big vibrating roller for thicker , can’t remember the joules of the roller but it’s orders of magnitude grater than a compactor plate type.
Good foundations make good buildings, id consider getting a reputable concrete contractor, easier on your back, big concrete slabs are bloody hard work ! You want young fit guys to handle the stuff, a 3’ pad will bugger me up these days, no more lines of concrete wagons thanks, and a pro with a bull float or a powerscreed makes it look easy.
Mark
Overland
Stainless
- Joined
- Nov 19, 2017
- Location
- Greenville, SC
You may need to pay attention to the frost line where you live. If I remember correctly, you want the edge of your slab below the frost line.
Bob
Bob
Is this a code minimum construction project? The foam must be rated for placing under concrete. There are different compressive strengths of the foam so you will have to decide on your loadings. A 4" floor doesn't leave room for error. You will have to double check the contractor as to thickness.
deltap
Cast Iron
- Joined
- Sep 3, 2004
- Location
- Wisconsin, USA
US Dept. of Housing and Urban Development (HUD) has a downloadable PDF book on Frost protected shallow foundations, heated and unheated. The foundation does not need to be below frost line if properly insulated. I have built both heated and unheated and know it works. Site prep is very important especially drainage. Building will not do well with water under the slab. If radiant slab is used, moisture will wick away the heat. A thickened slab edge 12 to 16 inches with rebar is a big design improvement over 4 inch slab. Soil conditions varry from place to place so rely on a local experienced builder and local codes.
howieranger
Aluminum
- Joined
- Jan 24, 2007
- Location
- Mountain Home AR.
I had to bring up the pad for my 40 x 60 shop 14" using 3/4 and smaller base. Every 6" I walked it in with my series 2 JD with the bucket full and then a vibratory plate compactor. The weight on the front tires did almost all of the compaction.
just Dave
Cast Iron
- Joined
- Jan 18, 2023
- Location
- Kansas City
6” min slab 4k mix min. You can build up with soil, but you need a 10 ton min machine to push it in a bucket at a time. I would make your floor 6” taller than you think you need it and ramp in, especially if your on flat land.
I do this stuff everyday. Main job is excavation and concrete contractor.
Definitely go with crushed rock with fines in it(minus) and compact in layers. 3"-4" is fine even for smaller compactors. Once you've got a layer packed, hit it again. Under slab prep is more important than the concrete if you meet the basics on the slab.
For the final layer of gravel, make sure it's pretty flat and level. You don't want any voids under the foam and a consistent thickness makes the concrete guys life easier. I always use the foamular ngx250, but I'm sure there are equivalents. Don't use foam that isn't made for going under concrete. Definitely borrow or rent a rotary laser lever for this part.
As others have mentioned, you will want a thicker/turned down edge depending on your frost line. Here it's only 12", but other northern states can be far deeper. Related to this, I would plan it out so you have at least 6" of vertical separation from the exterior soil to your finished building side walls. This will pay dividends long term.
Finally if you live somewhere where it rains, make a plan for your gutter downspouts. Don't just let the water run out right next to the building. This often causes issues down the line and it's not hard to deal with when you put the slab in. Here we typically run the downspouts into 4" PVC and direct it to a dry well for county requirements. If you local government isn't so picky, run it to daylight down hill from your buildings.
The concrete is up to you and your contractor. They should have a good mix design for a shop slab and you can add as much reinforcement as you want/can afford. As I mentioned earlier, many people go overboard on concrete thickness and rebar only to skimp on the sub grade.
Definitely go with crushed rock with fines in it(minus) and compact in layers. 3"-4" is fine even for smaller compactors. Once you've got a layer packed, hit it again. Under slab prep is more important than the concrete if you meet the basics on the slab.
For the final layer of gravel, make sure it's pretty flat and level. You don't want any voids under the foam and a consistent thickness makes the concrete guys life easier. I always use the foamular ngx250, but I'm sure there are equivalents. Don't use foam that isn't made for going under concrete. Definitely borrow or rent a rotary laser lever for this part.
As others have mentioned, you will want a thicker/turned down edge depending on your frost line. Here it's only 12", but other northern states can be far deeper. Related to this, I would plan it out so you have at least 6" of vertical separation from the exterior soil to your finished building side walls. This will pay dividends long term.
Finally if you live somewhere where it rains, make a plan for your gutter downspouts. Don't just let the water run out right next to the building. This often causes issues down the line and it's not hard to deal with when you put the slab in. Here we typically run the downspouts into 4" PVC and direct it to a dry well for county requirements. If you local government isn't so picky, run it to daylight down hill from your buildings.
The concrete is up to you and your contractor. They should have a good mix design for a shop slab and you can add as much reinforcement as you want/can afford. As I mentioned earlier, many people go overboard on concrete thickness and rebar only to skimp on the sub grade.
