Shed on skids-framing question

[bluedog225]

I had a short conversation with myself about whether to post this in the Bilge or here. Here won. Although the possibility of this workshop turning into a boat workshop is realistically a couple of years off.

When pressed, I can probably figure out floor joist spacing and sizing assuming a perimeter beam. But when I am trying to design a shed foundation (out of wood) that sits on two wooden skids, I'm over my head.

If the skids sit a couple of feet in from each wall, and the floor joists run perpendicular to the skids, then forces acting on the joists are all changed. The walls are pushing down on the ends of the joists and the center of the joist is being cantilevered up while still supporting the load of the material inside the shed.

Frankly, I've got no idea how to size or space these joists. Seems like I need to start calculating the weight of the wall and roof to see if the joists will support the wall and at the same time calculate the load on the floor. My attempts on figuring this out on google have been fruitless. I may just be using the wrong terminology.

Hope this makes sense. Would someone point me in the right direction for some education?

Many thanks

Tom

[TimmS]

Can you tell us about the size and use of the shed? also, why does it have to be on skids, and how far do you plan to move it?

[gibetheridge]

Lots more. Everything you can think of. How much
weight stored in shed, widows, doors, insulation etc.

[Ian McColgin]

This is easy. It's not like you'll have a huge overhang but in reality the skids, being in a bit from where the normal perimeter foundation would be, reduce the unsupported span. So if you build as normal for the expected floor loading and if the weight of your walls is not excessive, you'll be fine if maybe a little "overbuilt." I've done enough building moving to know that it's not that big a deal.

The one thing I'd do differently from normal static construction is the connection between the floor joists and the verticle frames. Here, make it more like the shelf and clamp you see in a boat's gunnel to deck connection. That way if you're dragging the unit about, you'll not worry about being gentle.

G'luck

[bluedog225]

Thanks. It's going to be roughly 12-14 feet by 20+ feet. 10 foot walls with a pretty steep (1:1) metal roof. 2x6 walls. Average loads with some fairly heavy localized stuff (like a table saw or caladonia yawl).

The skids are primarily to deal with deep and very expansive clay so that I can keep it reasonable level with a minimum of effort. Cracks open up in the earth that are 6 inches across and several feet deep in the summer.

Moving the structure is a possibility later. Nice to have the option.

[huisjen]

Rule of thumb: A beam supported on both ends can span 4x the distance of a cantilevered beam. So if the skids were 8' apart, the cantilever would be 2' on either side, for a 12' total. The trick here is that this rule assumes an evenly distributed load, and you'll have the wall load concentrated on the ends of the joists.

On the other hand, the skids will probably sink right into that expansive clay. Put down a raised gravel pad first maybe.

Dan

[Ian McColgin]

Maybe don't think shed. Think shanty barge. Then when you're tired of the mud you can drag it to the water.

[huisjen]

Ooooh! Dig it a pond!

Dan