Talk me into my shed foundation

[Hcooperrn]

After reading dozens of threads on multiple ways to build a shed foundation, I still can't pick a plan -- hoping for some help deciding.

I'm hoping to build a 16x24, gambrel roof, it will hold a mower, some small woodworking tools, space to build surfboards; nothing too heavy.

My soil is Texas black gumbo clay. I just put in an above ground pool, and after taking just two inches off, not looking forward to doing that again. Drilling 52 post holes for a fence was less than fun as well.

So I'm thinking I have two options, piers or skids. Pad is out due to cost and labor involved, just not worth it right now.

Piers would be on something like a 6ft grid (a lot of them, 12" and 3' deep). Pros are that I know it will be good, however, cons of extra cost and a lot of extra labor -- likely won't happen this summer.

Skids would be 4x6 treated/waxed on a built up layer of compacted gravel over landscape fabric, with a 4x6 treated/waxed retainer edge. Pros - cheaper, faster with the cons of risk of movement/sinking in the clay and any water retention in the gravel itself.

What would you do?

 

[readhead]

Skids. Better if you decide to move it latter. Make sure that the two center skids are 60"C-C.

 

[NUTTSGT]

What are your plans for the shed ?

 

[Hcooperrn]

Not planning on moving it at any point, too big and it would help the resale value a bit.

Use plans are just storage of the lawn mowers, some storage in the loft, and it will be lightly insulated to keep it comfortable enough for surfboard shaping.


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[Hcooperrn]

Any other thoughts? Anyone else built a shed this size on clay without issue?

 

[kaymccampbell]

Any other thoughts? Anyone else built a shed this size on clay without issue?

I had a similar one placed. I dug down a bit, with a ditch running away from where shed would go. Put down geotextile. Filled with gravel, including the ditch. More geotextile, and some nice round roofing rocks to look nice. Every 3-4 years the doors stick, and I jack the offending corner and jam some more round stones under the skid. Or, take a few out.

 

[MetalBuildingFun]

Skids, also placed on blocks to level and anchored. This is how you do it here in hurricane country for those types of buildings. Our little 8x10 shed was moved off it's blocks and pushed forward but still anchored into the ground when hurricane harvey hit us. New anchors, reset shed, quite a few dents from hail and we were good to go. Mine is a Chapparall brand shed I bought back in about 2009 or so. It has been great, it is built on 16" centers just like a house. We insulated and wired it for a/c and lighting.

 

[Rusty Fords]

For what you are attending on doing with it I would say on skids as well or on pier blocks. In my neck of the woods if it isn't attached to the ground they don't charge taxes on it do to it is movable which is sometimes a bonus!!!

In my location clay is an issue as well different doors close and open differently depending on the time of year.

 

[Bretny]

You dont need sono tubes, its a shed. I would lay down a layer of road fabric then compact a few layers of crushed stone with fines in it( this type of gravel is called may dif things) then use wide blocks under the 6x6 runners.

I may even pour blocks useing those big for forms for a shed this size.

 

[nadogail]

Logs or power poles for skids.

 

[Hcooperrn]

Thanks for all the replies.

I didn't specifically call it out, just implied maybe, I will be running electrical out to it (220v, 60a) to handle the tools I'll have in there, so I do need to protect against movement.

I wonder if a hybrid solution is what I need? A pier in each corner, and maybe one on each long side, with embedded bases to anchor the skids into. That would protect against wind movement, and hopefully to a degree, settling.

The rest of the length of the skids would then be on decent sized pavers over compacted gravel with fines to support the overall structure.

Probably a little overkill, but I could still move it/jack it if I used bolts to attach to adjustable post bases on the piers I think?

 

[Bert_]

One nice thing if it's on skids it's not permanent so no property taxes, at least that's how it works in Iowa.

A permanent connection to power would probably change that.

 

[Bretny]

How many piers or blocks really depends on the runner/girter depth and floor joist size. This is assuming your buying 24' runners.

 

[readhead]

Over 16' we laminate our center skids with four PT 2x6 and offset the laps. On the outside skids we use two PT 2x6 and offset the laps.

 

[matt_i]

Imo 16x24 is getting pretty large to be self-standing without some additional considerations for holding it together. The concrete hardpoints in the ground hold with ~2000psf bearing.

I think it could be done but with a lot of continuous metal X-bracing on every plane that will allow it. Use Simpson CS-16 or go hybrid and get a roll of 1-1/4" metal banding but that's not galvanized and will rust.

 

[Hcooperrn]

@readhead, not quite sure I'm following -- are you saying you only use laminated 2x skids? Or add 2x6 on the outside of a 4x6 in the center?

If I was doing beam on pier, I was going to use triple 2x6 beams. Going to skids, then, just trying to understand what you're describing. The pre-made sheds I've looked at have 4x6x12 skids with a 2x6x4 on each side of the joint, all then supported along the full length on the ground.

I was planning on 2x6 floor joists on 16" center with 3/4" T&G floor. With 5 skids, they would never span more than 4ft, which should be solid enough?

@matt_i -- are you saying metal x-bracing on the wall studs? None of the pre-made 16x20 or 16x24 pre-made sheds I've looked at have those -- they are all bare minimum with t1-11 siding. I was planning on sheathing the wall, then siding, as well as osb on the inside for a finished wall, which should make it pretty rigid? The roof will be 2x6 rafters (all the pre-built are 2x4) on 24" centers. I'll also have 2x12s on 24" centers on all but two of the rafters to create a nearly complete loft space.

 

[kaymccampbell]

If you're worried about frost heave, they make slip joints for PVC conduit. One of those under a 90° condulet, will allow for the vertical movement of the freeze-thaw cycle.

 

[readhead]

We use 6x6PT for our center skids up to 16' long. Over 16' we laminate four 2x6PT. 16' seems to be the limit for quality 6x6PT around here. For the outside skids we always laminate two 2x6PT. For 16' wide four skids is fine. The reason I mentioned 5' OC for the center skids is that is an industry standard and will fit on a shed hauling trailer.
You say you are not going to move it but things can change and having the option to haul the building may be very useful in the future.

 

[Bretny]

@readhead, not quite sure I'm following -- are you saying you only use laminated 2x skids? Or add 2x6 on the outside of a 4x6 in the center?

If I was doing beam on pier, I was going to use triple 2x6 beams. Going to skids, then, just trying to understand what you're describing. The pre-made sheds I've looked at have 4x6x12 skids with a 2x6x4 on each side of the joint, all then supported along the full length on the ground.

I was planning on 2x6 floor joists on 16" center with 3/4" T&G floor. With 5 skids, they would never span more than 4ft, which should be solid enough?

@matt_i -- are you saying metal x-bracing on the wall studs? None of the pre-made 16x20 or 16x24 pre-made sheds I've looked at have those -- they are all bare minimum with t1-11 siding. I was planning on sheathing the wall, then siding, as well as osb on the inside for a finished wall, which should make it pretty rigid? The roof will be 2x6 rafters (all the pre-built are 2x4) on 24" centers. I'll also have 2x12s on 24" centers on all but two of the rafters to create a nearly complete loft space.

Use 16ft 2x8 floor joists and use just 3 runners. The runners can be 6x6 or just make a girter out of 2x8 that dont span more than 8ft. With 8ft 2x8 you use 3 lengths. Do this 2x per runner and have two 2x8x12' in the middle. The girters should prob be PT but if you separate them from the concrete blocks with say a piece of trex and put the siding down over the ends they dont really need to be. Keep your shed well above ground your floor joists dont need to be PT either.

Once you start useing PT wood where it's not really needed you should be useing hot dipped galvanized hardware or some other form of PT rated hardware..and that stuff gets expensive quick. Normal zink isnt going to cut it.


We are building a 20x24ft cabin on piers and pretty much up sizing everything from what I'm telling you on the girter size and floor joist depth. A building is only as good as its foundation.