Shed foundation?

[deerminator]

We're looking at buying a 12 x 20 foot barn style shed that will be trucked in to our home site. The company recommends putting in a crushed gravel foundation for it that obviously should be completely level and thoroughly compacted. I'm also considering a cement pad instead since it may not be much more in the grand scheme of things when you consider what class 2 or crushed granite costs. And the time and effort with leveling it and the cost of renting the compactor. Anyone with shed building or placement experience have any thoughts on this? The shed itself sits on treated 4x4 skids underneath.

Also, I've checked with the local building officials as I know a permit will be required. They say we can choose whatever foundation we want so long as it is secured somehow such as bolting to cement or using mobile home tie-downs if not.

[LightningBG]

IMO, if the shed sits on skids, and presumably has it's own framed floor, the concrete could be overkill. About the only thing you'll gain is weed control.

And the cost may be more than you think. It would need forms and ideally a skilled person to screed and trowel it (although it could be done yourself.

For a pad that size, 4 inches thick, you'd be looking at 2.96 yards. That much would fit in 1 truck, which would probably run about $300-400 if I had to guess. The delivery is actually the expensive part, so you could make the pad bigger (4-5 yards worth) for very little extra. Otherwise for bagged concrete, you'd be looking at about 134 - 80lb bags. (buying the bags doesn't really save any money.)

[cavalierowner]

When I built my shed about 13 years ago, I just used treated 4x4's around the entire perimeter, 2 high below grade and 1 above grade. They just sat on top of the topsoil that was there. I didn't really care if it moved a little with frost. Then a conventional treated wood joist floor with treated plywood. I didn't use any tiedowns because the shed is in a heavily wooded area, so I wasn't too worried about wind. I didn't need a permit because I was under 120 sf (barely!), so I don't know what the City might have required. At any rate, so far the treated foundation is holding up well. The only thing I had to do was dig in some heavy galvanized wire mesh; darn critters were digging down below those 2 below grade 4x4's to get under the shed.

[deerminator]

Thanks guys. I think I might go with the crushed granite underneath. I need to do some leveling anyway so the rock makes sense. And I think I'll need less than I thought. Maybe a load. I recently paid $850 for two loads of crushed granite that included a couple hours of skid loader time to smooth and pack it down nicely over problem spots on my 1/4 mile long driveway. Man, that stuff holds versus the class 5 gravel but it's pricey. So I'm hoping I'd be half that or less for the pad area. Plus I'm reading the drainage would be better with the crushed granite versus the concrete underneath.

[LightningBG]

I'm guessing most of that $850 price tag was the skid time.

If you really wanted to do as much as possible yourself, you could have it delivered and dumped in the correct area, having them start at the back of the area and pull forward as they dump. That will get it near the correct area. Then spread with a shovel and rent a plate compactor to pack it down. Around here they run about $85 for a day.

[deerminator]

Nope. The skid time was less than 1/4 of it. And this was for two dump trucks. Crushed granite is not cheap these days. If I remember correctly, 5 times the cost of class 5 and that was true everywhere I checked. I have had them spread dump before for a gravel patio I made near the lake. I might try that option there as well with the compactor. Thanks for the idea.

[Bjjams]

2 years ago I did the same thing except for a smaller shed, 10x10, and I used 4 yds of crushed concrete. Much cheaper than crushed granite and just as stable. I borrowed a plate compactor and did the leveling by hand.

[deerminator]

Ah, crushed concrete could be another option. We looked into that for bolstering the driveway but the possibility of metal being in it turned us off. Still, if its under a shed and you're not driving on it, then there are no concerns.

[Surface Tension]

I'd look for some crunched recycled concert, crushed recycled asphalt, crushed limestone, or class 5. If your putting down a slab you'd remove all organic materiel off.

In this case rent a sod cutter, set it deep and get that out of there.

Use one the materials I mention and then lay that down, compacting as you go till you get at least 6" above grade. I'd go further and lay down a moisture barrier. Believe it or not you'll get a lot of moisture coming from the ground. I'd get a moisture barrier some where in that lift.