Shed foundation quandary

[MJ]

In a week, I'll be building a 10x12 shed.

The plans call for a on-grade foundation with 6x6 skids. My property is slo ped. From high pt to low pt is about 8 inches. I called out a guy and asked about pouring a slab. After I got over the price objections ($3k), he and I talked about cheaper suggestions. He said, oh, we could do Sonotube pier s. I agreed but the project at that point stalled as I lost the person who was going to help.

Anyways, I found another person and he said he and I would do the foundatio n layout, digging, etc. ourselves. I told him my soil is kinda hard (clay a nd possible sandstone). No problem, just water the area and it will soften. I did a test dig yesterday and the water didn't drain for over an hour. Hm m, this is gonna be tough going.

Here's where I'm at. I could go with on-grade foundation using solid concre te blocks to level up the low spots. Not a problem for me, easy to layout a nd make happen. Or... we could get a power auger and drill the Sonotube pie rs. My helper who is a expert carpenter is away on vacation until two days before we start, so I can't get his opinion.

Which way would you go? Block or tubes?

My only concern is earth movement. Earthquakes are possibility. But a rare one. Would one would see a wood foundation come off a cement block pier in a minor (less then Richter 2) quake? I thought of drilling into the block a nd holding the joists with anchors. Can you drill solid block?

MJ

[Ed Pawlowski]

Here is some info on site prep. I have crushed stone

I was going to get a 10 x 12 too, but opted for a 10 x 16 and I'm glad I did.

[-MIKE-]

You might be trying to NASA-tise this. :-)

8 inches is nothing, one concrete block. You could dig one side down only 4 inches and it wouldn't look too high on the other side.

As for a foundation, where in the country are you? If you have a lot of freeze and thaw, you may want a foundation under the freeze line. If you don't have long hard winters, you could hand dig shallow pier holes or wider pads for crushed stone and a concrete post block. I'm in TN and I dug shallow pads filled with crushed stone, on top of which sit flat cement blocks that the wood skids sit on. My shed is a bit smaller than yours and hasn't moved in 12 years.

I think block on stone would work for you and you could do it yourself in an afternoon.

[Lonesome Dove]

A 12 X 16 is the ideal small unit size. Makes it much easier to handle

8ft boards and plywood if you're going to have a table saw. Where we are, the general practice is pole buildings. If you have to deal with a slope, that's the way to go. Just rent a power auger, dig the holes, set the poles, rest for a week and then frame it up and finish it off. Even if your only going for storage space, you never have enough. (G) ** Lonesome Dove

[FrozenNorth]

Agreed, our shed is only a 10x10, but I just built a 2x8 frame on 16" centers covered with ply and sat the whole thing on four pier blocks, shed went up from there and this Toronto Canada. The area was level though.

[ChairMan]

In news: [e-mail], MJ belched:

Personally, i would do the Sonotubes. I had built a 16x20 and they used concrete blocks. I have to have it jacked up and leveled every couple of years because the blocks slowly sink into the ground. I wish now i had done piers/sonotubes I'm getting ready to jack it up again and I'm going to replace the 4x4 skids with steel I beams so that I can drill holes in the ends to accomodate a cleavis hook to hook the farm jacks to and make it easier to jack up with less stress on the building. Plus the I beams won't warp/twist like the 4x4s and hopefully stay straighter jmo & ymmv

[knuttle]

Two years ago I had a 10 X 12 shed built for lawn equipment. It is built on a 2 X 6 floor with 2 X 6 on 16 inch centers. It was leveled on blocks. (20 miles east of Raleigh NC in a rural area)

While there has been a lot of good advice, the one thing that must be consider when building are the building requirements for the community you live. In this area there are no building requirements or permits required if the building is 120 square feet or less. If I had run fixed electricity to the shed I would have been required to get a permit.

Depending on the area they may have unique ideas on how sheds are constructed including the foundations they are built on.

There is another considerations. While others have made comments on what they have in their sheds, I don't believe you said how you were going to use yours. If you have a lot of heavy equipment table saws drill press,grinders, etc, with a lot of vibration I am not sure I would consider blocks. Though you would not believe what some people consider foundations for houses. Some of the old houses in the south are built on a pile of stones. You wonder how they still are together after 100 years. Some look like removing one stone would bring the whole house down.

[Ed Pawlowski]

Now may be the time to do the Sonotubes. Drill the tubes right next to the shed. Make the steel beams a foot longer to sit on the concrete.

[Swingman]

The most important element needed to effectively answer the OP's question.

[woodchucker]

I would have a few tons of 3/4 gravel delivered.

That's what I did...I leveled the gravel, the shed has been fine, and dry from all the gravel... which allows water to get farther away from the shed than being on the earth.

[MJ]

I already have a fully wired shop. This shed is just for excess wood, garde n equipment (no tractors), and misc. stuff from the garage so the SHMBO can park her car into her side of the garage. No machinery that will be operat ed. I might store some light equipment in there, but I'll use it in the sh op.

MJ

[MJ]

One of my concerns. My soil is clay with possibility of sandstone. Would you think a power auger can get through all of that?

MJ

[Keith Nuttle]

From what you are saying about the soil, size, and things that will be stored in the shed I think I would go with the properly leveld blocks. It will probably be there long after you leave.

[clare]

Frost? If so, sonotube below frost line, and cast your anchor bolts into the concrete of the sonotube pilings.

[basilisk]

Wow $3k for a 10x12, I'm always shocked when I see how much it cost to do things in other parts of the country. This is an order of magnitude greater than it would cost in AL.

I know there is a lot of differences in areas, frost depth, general labor cost, cost of concrete, difficulty of grading and prep and site access, but even worst case in all areas, $3k seems excessive.

It would be hard to beat sono tubes below frost line and cast in place anchors.

basilisk

[knuttle]

You can build a 10 X 12 building for $300. I don't even think you could build for that using scrap lumber. My 10 X 12 barn roof shed cost about $2500 installed.

2 X 4 X 8' are about $2.5 /ea 4X8 3/4 pressure treated plywood about $35/ea.

[dadiOH]

I take it you meant, "You can'T build a 10 X 12 building for $3000".

OP was talking about $3000 for a *SLAB*. JUST the slab.

[HerHusband]

$3000 for a 10x12 slab? Ouch. Even if I built simple forms and dug it down so it was a full 12" thick all around it would cost less than $800 for 5 yards of concrete here (Washington State).

A slab that size is not difficult to do yourself (with a part time helper). Just build the forms, make sure they're square and level, and have some concrete delivered. Use a board to work out any air bubbles during the pour, then use a long board and your helper to screed off the concrete level with the forms.

You're not building a house, so I probably wouldn't worry about frost lines. Just let it float on top of the ground. It may move up and down with the freeze/thaw and end up slightly out of level, but so what? It's a shed.

For small pours like this, I prefer to use companies with trucks that mix concrete right on site. There's less waste and you only pay for the concrete you use.

Last time I priced an 8x12 shed, it was cheaper to pour a (4") concrete slab than to build a wood floor with 2x6 floor joists and plywood. Concrete is also nice if you're storing outdoor equipment such as mowers or tillers, since you don't need to worry about water running off onto the floor.

I would make the upper edge of the forms with 2x4's, then add filler boards underneath on the low end to accomodate the slope. You don't need to dig the whole area down to the same level, but I would probably try to dig out flat stepped areas so there's minimal risk of movement on the slope. I would also dig a little deeper around the perimeter to make "footings", how deep is up to you.

Plan to install some "J" concrete anchor bolts after screeding the concrete so you can bolt the shed to the slab once it's set up.

Even if the shed shifts over time, or you decide you want it in a different location, you can always move the shed and pour a new slab like we did:

Anthony Watson

[Unquestionably Confused]

Go back and read it again, Keith.

it was $3k ($3,000) for JUST the concrete pad. AFAIK, the OP has not even discussed the cost of the building itself.

[Swingman]

On a 10 x 12 slab you will also want to factor in wire mesh/rebar (#3 on

16" centers would be my preference for a slab that size) if you want it to last ...