How to ensure plywood sheathing hits joist on center?

[John Nicoletti]

I'm smacking myself on this one....

A while ago I built some shelving and got it fitted with plywood, ensuring that the plywood was flush at the front and ended halfway on the joist before starting the next sheet. However, for the life of me (it was a while ago), I cannot figure out how I did it.

I'm looking to build a 10x16' shed. I have framed everything out in Sketchup, and all is going well. However, without exhibiting waster, I cannot figure out how to get the plywood to land on the center of the joists, making sure every edge of the plywood is secure.

The floor frame will have 2x6s, 12" on center. When I lay down a 4x8 sheet in sketchup. it covers 8 joists, completely. Therefore, when I go to add my second sheet of ply, the connecting edge has no support.

I figured I could trim 3/4" off of the first sheet, allowing me to hit 7.5 joists, but then I will be short on the other end...what secret am I missing that is making this way more complicated that it should be?

It's quite embarrassing that I can frame out the entire building....but fail at the floor sheating

Any clarification would be appreciated!

[Paul F Franklin]

The floor frame will have 2x6s, 12" on center. When I lay down a 4x8 sheet in sketchup. it covers 8 joists, completely.

Something's not correct. If the joists are really 12" from center to center, it will be 49.5 inches from left edge of starting stud to right edge of ending stud. If you lay the plywood starting in the center of a joist, it will end in the center of a joist. If that doesn't happen, then either they aren't on 12 inch centers or your plywood isn't 48 wide.

Now perhaps you are thrown off by the fact that your first joist needs to be spaced 3/4" closer to the rim joist so the first sheet of plywood covers the entire rim joist but still ends in the middle of a joist.....

[Sam Murdoch]

Your layout needs to start from the outside of the first joist to the centerlines of the remaining - not all centerline to centerline.
If I understand your question...

[John Nicoletti]

Now perhaps you are thrown off by the fact that your first joist needs to be spaced 3/4" closer to the rim joist so the first sheet of plywood covers the entire rim joist but still ends in the middle of a joist.....

Ding, Ding, Ding - we have a winner! Thank you!! That was my missing piece. I was going from the outside of the rim joist, 16" until the starting edge of the next joist! Doh!! Something so simple...

Got it all fixed up, going from the outside of the rim joist to 15 1/4" until the edge of the next joist, and then 16" after that.


Now that everything is lining up correctly...What do you think is the best floor pattern? The boards are running perpendicular to the joists, but I know typically, you don't want joints to intersect. This is again, a 10'x16' structure.
Floor 1.JPGFloor 2.JPG

Thank you again, Paul!

[George Bokros]

I would change the size to 12 x 16 if you can. Saves waste and time.

[Paul F Franklin]

Glad to help.

You don't want any four corner joints if you can avoid. So do 4 4 2 on first row, then 2 4 4 on next row.

[Bob Michaels]

I may be misinterpreting your drawing, but, are the small rectangles under the sheets of plywood supposed to be floor joist locations? If so, the decking is not running perpendicular to the joist. Kindly clarify.

[Clint Bach]

Actually none of the above is standard floor layout... Cut one of the 4 x8 sheets in half croswise to make 2 4 x 4 pieces. Cut one sheet in half lengthwise making 2 2 x 8 pieces. Start with the two 2x8 sheets on one of the long sides end to end. Then put a 4 x 4, then a 4 x 8 and the other 4 x 4 end to end in the middle. Then the last two sheets end to end on the last row. put the narrower sheets on the wall that needs the least strength.

are you using tongue and groove flooring plywood? The floor should use exactly 5 sheets of plywood.

hope this answers your question...

clint

[Clint Bach]

Oh, and the joists should (read must) go across the direction of the plywood not lengthwise. In your case 10 foot joists.

clint