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In my particular case, I'm building a tiny shed. I'm using ungrooved 3/4 inch treated plywood and no glue, if that makes a difference.

I'm not sure what the relevant units are either. Pounds per square foot? Screws per 4'x8' sheet?

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    I think the answer to every how many ... question is 42. – bib Apr 19 '16 at 15:20
  • So this is a bad question because the answer is "it's arbitrary"? – Ryne Everett Apr 19 '16 at 15:25
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    It depends on a lot of factors - what is going over the plywood? how is the subfloor structured? what will sit on the floor? how long do you want it to last?. There are also several other assembly questions that come into play (which you may have already dealt with), such as expansion spacing, sealing, type of screws, etc. – bib Apr 19 '16 at 15:36
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According to Table R602.3(1) of International Residential Code (IRC), subfloor fastener schedule is as follows:

  • 3/8"-1/2" panels. Use 6d common nails, spaced 6" apart on edges and 12" apart in the field.

  • 19/32"-1" panels. Use 8d common nails, spaced 6" apart on edges and 12" apart in the field.

  • 1 1/8"-1 1/4" panels. Use 10d common or 8d deformed nails, spaced 6" apart on edges and 12" apart in the field.

NOTES:

  • You can use screws (and I recommend you do), however, they must be equivalent to the nails listed in the code.
  • "edge" refers to the perimeter of each panel, while "field" refers to fastener not at the edge of each panel.
  • If you're building from a kit, you should follow the manufacturer's installation instructions.
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    +1, I feel like when we used to do this, we used 4" on the perimeter and 8" on the field, but we also joked that the local airport had to realign their compass when we finished a project. Use the above specs as minimums and upgrade to screws to avoid squeaks. And use construction adhesive between the joist and subfloor, too. – BMitch Apr 19 '16 at 20:13
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mostly correct

if figured for a horizontal diaphram then the answer would depend on your lateral calculations...then you may have a different nailing pattern and stagger...

but 6 and 12 is generally acceptable in most conditions

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    Hello, and welcome to Stack Exchange. This is interesting, but hard to understand; would you add a few sentences and make your post clearer? – Daniel Griscom Jun 8 '18 at 20:56

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