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I am in the process of building a roughly 12' x 16' shed/workshop. It is going to be a pier-and-beam design. There are 8 concrete piers, 4 on each side, that will support 2 4x12 beams. The span from the outside of one of the beams to the outside of the other is roughly 12'.

One possibility for joist/subfloor design:

  • 2x10 doug fir joists, 16" oc
  • One blocking sequence down roughly the middle
  • 3/4 inch plywood
  • Some form of construction adhesive between joists and plywood
  • Screwing and/or nailing plywood to joists.

I think it's a fairly sound design overall, but I'm not sure how much "give" there will be in the floor after completion. Do you think that would have a lot of bounce, or should that be plenty?

According to the IRC, both southern pine and doug-fir-larch should be able to span 12 ft for 40psf live load and 20 psf dead load at 16" oc. See: https://codes.iccsafe.org/content/IRC2015/chapter-5-floors?site_type=public .

Will this be sufficient to have a floor without significant bounce?

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    This all sounds good, and is slightly better than the design that I recently used and I didn't have bounce. You want to keep the 16" oc, and you don't want any less than 3/4" plywood. I thought I might get away with 1/2" ply, but that was terrible. I used all PT wood for the floor and foundation. That said, I don't feel like I have enough framing expertise to make this an "answer".
    – JPhi1618
    Jul 17, 2019 at 19:53
  • Thanks. For your building, what was the joist span?
    – bddicken
    Jul 17, 2019 at 20:30

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I recently build a 8x14 shed using 2x8 pressure treated joists and there was no bounce. It felt solid with a 3/4" PT plywood floor. Your design is larger, so I agree with the 2x10 that you spec'ed. I don't think you'll have an issue it all.

I was originally going to try and save some money so I mocked up a few combinations of 16" oc and 24" oc with 3/4" and 1/2" plywood since it was "just a shed". The joists 16" oc with 3/4" ply was the only combo that felt solid (as expected). The shed had a small 4' "porch". For that I did use 24" oc joists with 5/4" PT deck boards. That was a stretch that I wouldn't have made for a full on deck, but it was fine for the small porch that would only have a few people on it with no static load.

I had 6 piers, so your 8 sound good. The only thing I second guessed is the depth of my piers. I was digging alone, and manually so I didn't get them as deep as they should have been. I didn't notice a problem, but I would suggest getting the recommend depth in your area for sure.

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  • Sounds good. In my case I wanted to use tongue & groove flooring, so I used PT joists with building wrap over them to keep moisture to a minimum.
    – isherwood
    Jul 17, 2019 at 21:09
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A follow-up, in case anyone visits this later and is curious about the answer.

Since posting, I have gone ahead and build the floor. The span was a little under 12' (about 11' 6.5"), and I used 2x10 joists with joist hangers. I used 23/32 plywood for the subfloor, and used liquid nails plus 2" deck screws to attach the plywood to the joists. It is solid enough for my purposes! If someone has a follow-up question, feel free to ask.

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