Best foundation for shed

[macpiano]

I'm thinking about doing a shed. I want concrete for the base but all these sales guys say to use 4-5 inches of gravel then I think it gets 4x4's then the ply. So my wife thinks its a waste to pay for concrete.

The area that the shed will be does get a lot of water because it's downstream from the yard behind us which is higher.

Looking for suggestions.

[daveferg]

I think you just answered your own question. If your shed site is downhill of drainage, putting it on a wood skid is asking for trouble-----if the ground doesn't shift, the wood will eventually rot. Besides, if you plan on storing anything liquid, like paint, or gas powered garden tools---hence oil and gas, a wooden floor is a very bad idea, as it will absorb all that stuff and look like a mess---if not a fire hazard.

I wouldn't hesitate doing a concrete slab and if water could be a problem, you could always lay in a length of french drain between the hill and the slab, parallel to the flow.

Digging down and installing forms is a snap. If the site is close enough a concrete truck with a chute extension could reach it----you're lucky---otherwise, a couple of friends with wheelbarrows helping you for a couple of hours of good cardio-vascular exercise would do the trick. I also installed "J" bolts (locations marked on the forms) so it was pretty easy to set your sill plate. As my slab sat slightly above grade, after I remove the forms, it was very easy to form for a ramp----small enough to use bags of readi-mix.

[Herb G]

Concrete all the way. Make sure it sits proud of the surrounding ground by a good 8", & you'll be golden.

Why 8"? Because over time, it will fill in.
DAMHIKT.

[Mr_Mike]

Depends.

Here, permanent structures greater than 120 sq ft in silhouette (includes eaves) requires a permit. Most folks do pre-built toughsheds on skids to avoid that.

Given your moisture, I'd likely do concrete piers and elevate the floor.

[macpiano]

No permit needed here up to 200 sq feet. Deed restrictions say 10X12 max

[Woodenfish]

The sales guy' advice is good. I have a 10' x 12' barn shed installed in my backyard the same way. Although, mine is on ground contact rated pressure treated 4x6's. After 16 years of service there was some sinking. I jacked the shed up with a farm jack and added more gravel to level. The skids were in as good of condition as the day they were laid. This was two years ago.

[macpiano]

So is it gravel, 4x6, then plywood?

[Woodenfish]

macpiano said:

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So is it gravel, 4x6, then plywood?

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Gravel, 4x6 ground rated pressure treated beams, 2x6 pressure treated floor and rim joists at either 12 or 16" OC depending upon your needed load, 3/4" pressure treated plywood floor decking. The siding will come down the wall and covers the rim joists.

My shed is 10' wide and 12' deep. The barn style shed has its raised peak and doors on the 10' wide walls. There are three 4x6 beams 12' long. The 16" OC floor joists cantilever the outer beams by 12".

[GHR]

macpiano said:

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So is it gravel, 4x6, then plywood?

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I think it depends more on how much your shed costs and what you want to use it for.

Concrete seems too permanent for me. Gravel is too permanent also.

I have used 4x4 treated posts - corners of a shed, extending a foot or so into the ground resting on a sack of concrete mix. But that is often too much.

[mike4244]

Piers will work for the foundation. Sonotube probably 12" diameter and 36" below grade ,8" above grade.Depending on the size you may need as little as four piers.You need to know how this sheds floor is framed to know how many and location of piers.I'm assuming this is a store bought shed,they are usually set on a bed of gravel.The shed is slid off the truck.
Might be a concern for the driver to get the shed on your piers.
If you have gravel down for the bed you can still raise the shed to sit on solid concrete blocks.I did this for my neighbor. I used 2 bumper jacks to raise one end at a time.Slipped donage under one end at a time .Raised the 10 x24' shed 8" and slid the block under.
If the soil drains well either method is fine. If the soil is clay based then I would only use piers.

mike