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Connor77 09-22-2010 08:44 AM

Slab for Shed Help requested
Slab for 20 x 16 shed
I'm building a 20 x 16 shed in southeastern MA and my concrete guy wants to put 4 12" tubes at the 4 corners and then pour the 4" slab and the tubes all at the same time. The heaviest thing that will go in the shed is a small subcompact tractor. The balance will be misc yard care stuff, bikes, tools etc

My questions are:

Are 4 tubes enough? I would think I would want something in the center
In terms of reinforcement he wants to use wire. From everything I've read I'd be better off with rebar - is this overkill or necessary?

Any other tips for making sure my slab is done correctly? I'd prefer to do this only once.

papageek 09-22-2010 09:26 AM

Hi Connor, I don't mean to hijack your thread, but I just started a similar project and I think the questions I'm about to ask will benefit both of us.

My shed will be 18 by 9, built on an existing concrete slab ( an existing dog run that is sloped for runoff, but that is a different topic! ). Plan A is to lag pressure treated 2 x 4's to the edges of the slab, erect the framework with fir stubs, then the first course of horizontal plywood will also be pressure treated.

Here are the questions I am adding to the mix here.

When lagging the base plate to pad, should I put any kind of membrane or sealer under the 2x4's, or just lay them directly on the concrete?

I'm going to put siding on the outside, should the first course of plywood end even with the bottom of the base plate, or should it overlap the concrete a little? If so, how much? Plan A, end it even!

I plan to extend the J channel and starter strips about 1/4 inch below the plywood. Is that sufficient?

Again Connor, hope you don't mind combining our questions!

Daniel Holzman 09-22-2010 11:43 AM

This reply is addressed to Connor only. There have been numerous posts regarding the advantages/disadvantages of rebar, mesh, or no rebar in concrete slabs. I suggest you search the forum and digest the comments, there must be close to a hundred of them by now.

As for the four 12 inch sonotubes, if they are being placed to support vertical posts, that makes sense, however there is no way to know this unless you post a diagram of the proposed framing for your shed. The tubes do absolutely nothing to strengthen the four inch slab, which is supported entirely by the soil placed under it. See previous threads for full discussion about proper preparation of the subgrade under an exterior slab. Therefore, if there are more than four vertical posts in your building, it may make sense to add sonotube footings under the posts, this is something you should discuss either with the architect of the shed, the engineer, the building inspector, or if you have none of the above, you may want to consider hiring one.

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