plywood subfloor question

[duckdude]

the carpet guy was replacing some carpet. it's laid down on a plywood subfloor. i noticed one gap in the laid down panels that you could peek into the basement thru.

you could also get a ruler thru the gap & measure the plywood thickness.

i was shocked to realize it wasn't that thick.

the panels are stamped 23/32, and tongue and groove - google'ing it - it seems the

23/32" is the same as 3/4 - but these panels are NOT even close to being 3/4" thick ...

now i must be missing something here in the way thickness is depicted.

should the panel really be 3/4" thick (ie. measured on a ruler), or is there some "trade" custom in measurements of plywood subfloor thickness that is used ? i would imagine an actual 3/4" thick plywood panel would be a very heavy dead load on the joist.

it actually measured on the ruler a little less than 1/4" thick - and the blueprints call for a standard 40 psf load limit.

[marson]

the panels should indeed be 3/4" (well, actually 23/32) measured on a ruler. Are you sure you are measuring the full sheet, and not bumping the tongue with your ruler or something? if it was actually 1/4" thick, you would definitly notice the flimsyness and there would be bellies between the joists.

[tbasc]

You may be confusing the structural deck and the underlayment. TB

[tinacci336]

If it was 24/32 then it would be exactly the same as 3/4. So 23/32 is just 1/32 thinner than 3/4 and a big difference from 1/4.

[duckdude]

well, there was a small gap in between 2 panels, and i could stick a ruler into the gap (and could peek thru it to see the basement). so when i stuck the ruler into the gap, and measured the plywood thickness at that gap edge, it was about 1/4" or so.

but yet the plywood panel underneath is stamped 23/32, tongue & groove.

the panels are all flat and don't seem to be flimsy, so it's a mystery that made me ask if i'm measuring it wrong.

so if it really was 1/4" thick, i'd know it for sure ??

the joists are 2x10's 16" o.c. (and some areas are double and triple joisted, and there are wood cross braces in between most of them - there's a fireplace in the same room) with those plywood subfloor panels.

[Eric Tonks]

You should measure the plywood by putting your ruler down into the gap so that it touches the top of the joist, then measure the thickness to the surface. I am sure it will measure close to 3/4".

[Sacramento Dave]

Some subfloor is 5/8" thick panels. I would be more concerned with be able to peak into the basement. Sounds like somebody went off layout. I would nail a 2X4 alongside the joist then nail the panel down.

[John Hines]

Tongue & groove means the edge of the plywood, at the mill, has a 1/4" cut in the top and bottom sides, leaving the middle 1/4" to stick into the slot cut in the other edge of the next sheet of plywood.

So if you have a slight gap between the sheet, but not enough to expose the whole edge, you could measure just the top cut on the T&G.

It makes for a stronger joint to have the two pieces interlock.

[ronm]

you could try removing a floor register and measuring there.

[Chris Lewis]

According to John Hines :

[Or the reverse ;-)]

Indeed.

It's also possible he's seeing a ripped off edge that doesn't quite meet, and has been undercut by a chunk split out of the underside of the ply.

In any event, 1/4" floor sheathing would be more than flimsy. If you stomped on it, there's a good chance of going through. You'd get a very queasy feeling walking on it.