Gravel under concrete pad

[getindirty]

Rock is great but pricey and unless it is the crusher run it is tough to compact. Sand works very well and lowers your install cost. The slab foundation idea's noted does not need to be applied as you are building a pole barn. The concrete will be "floating" inside the shed and not bearing any of the construction weight. I will agree that you should install a vapor barrier and consider a under slab and perimeter insulation if you want it heated. It will raise the concrete height 2". Rebar is awesome if you are parking a dump truck on it. Wire mesh (remesh) works well for everyone else. Tell the contractor building the shed where to set the rim board based on slab insulation and concrete thickness. I used a mini-excavator to dig the perimeter insulation after the framing was complete (it took two days to install).

Insulating Slabs

http://www.eere.energy.gov/buildings/building_america/pdfs/38309.pdf

Good luck.

 

[getindirty]

I forgot to add that after the post have been set you will want to "water" the post holes. You will be amazed at how much settling will occur. You can back fill the post with rock and or sand to lessen the amount but if you backfill with dirt it will take a few "waterings" to get the settling to quit. Unless the framing contractor throws the dirt from the post holes outside of the shed you will need to re-level some before the area is ready for concrete, so you might want to just get it close to level, build, then finish the grade from the inside. CUT to the rescue!

 

[SkunkWerX]

I'm over here in Maryland, not far from NorVa.
I had a similar issue with my 30 x 40 pole building.

I made up at least 4" corner to corner using gravel. Maybe 5".
7" is a bit much, but, you can also make up an extra inch using the poured cement, also.

I used wire AND rebar and tied it.

In this area gravel is about the same cost as sand or crush.
if you wanted to put down a couple inches of crush, then add gravel to make-up the rest of the difference, that would work.

In this area, with all of the various types of soil, I am leary about using compacted fill dirt.

Finally, if possible cut another 2" off of your high side, then the gravel can do the rest.

 

[rutwad]

I've roughed out a site for a pole barn to store my tractor and for a shop. The lower side of the site is about 7 inches lower than the upper side (side 2 in the attached picture is 7 inches lower than side 1). I'm thinking of using gravel to make up the difference when I go to pour the pad. Assuming 3" of gravel under the upper side, this means the lower side would have 10" of #57 gravel under the pad. Do you see any issues with this approach? Or should I just take the time and completely level the site before applying the pad gravel?

I am NO expert, barely even familiar with concrete construction. BUT I would cut down side 1 so the slab will be about flush with the ground. If you pour a 3 1/2" slab, then side 2 is only 3 1/2" low. Pour a 6" slab and you won't have much fill to worry with at all on side 2. I would not use gravel, rock, crushed stone, or any similiar material as a foundation. I would probably level what was there, but if I had to bring in material it would be sand.

I have a 30' x 40' homemade 1/2 shop & 1/2 carport. I had more than your 7"'s of fill for side 2 and I used red clay.

I leveled the pad from side 1 to side 2. I sloped it from the (front end of your truck side) down to the 1-2 side so water doesn't stand. Depending on the weight of what will be on the pad, and the type of ground should determine alot. I cut about a 1' deep footing around the perimiter and tied rebar here. I set the poles with scrap metal welded randomly at the base. I poured the holes with cement mix, but not up to the top. Once it cured, we poured the slab (wire had been installed) which ran into the pole holes to tie it all together. So far, so good. It's been 5 years and no problems yet. Only regret was that I did not put enough slope on the pad (only 2"'s across 30').


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