Plywood flooring

[MIStructE_IRE]

In a domestic situation, does 1/2 inch ply for joists at 12 inch centres sound right?

Ive never gone this thin with ply but the architect is looking for the thinnest buildup.

 

[XR250]

I believe it is rated for 16" O.C. max. Look at the span rating on the back of the sheet.
That being said, at 16" O.C., it feels spongy. Never tried it at 12" but I imagine it will be OK.

 

[skeletron]

No doubt that you can make 1/2" plywood work for 12" o/c ... for strength and possibly deflection. But vibration is the #1 issue here in residential. I wouldn't do it simply because the serviceability will be the issue that gives you a callback to fix it in a few years.

 

[Agent666]

The ply as skeletron eludes to does a reasonable job of also distributing point loads on one joist to the adjacent joists in reality. Resulting in a stiffer feeling floor. This effect can be reasonable, but diminishes with thinner ply thicknesses. Also of note is in this part of the world thicker plywood tends to have more plies in both directions, a 12mm ply is 1/4 the stiffness of a 19mm ply in the direction of the span based on a quick look through some manufacturers data. This effect on the floor stiffness would be substantial I would think.

Also consider if your floor is a diaphragm there maybe limitations on the thickness with respect to fixings, etc.

We don't use anything less than 19/21mm typically, irrespective of the span for timber floors.

I find it hard to believe 7mm extra thickness is really going to matter to the architect. If it does they can find it elsewhere.

 

[milkshakelake]

Agreed with Agent666. The tiny extra thickness shouldn't matter. In the end, the underlayment, floor finishes, gypsum board at ceiling, or a number of other items will determine the thickness, and nobody can really see or feel the 7mm difference.

 

[phamENG]

It'll work (though check the span rating as XR said to be sure). While 3/4" subfloor is the norm now, I've been in lots of homes built in the 80s and 90s with 1/2" ply - last month one had joists at 24" (part of the reason I was there....).

If this is a high end residence, I would be leary of doing it for the reasons mentioned. You'll get more vibrations, and if the framers aren't spot on with discreet demising wall supports, you'll get some serious long term movement under those walls. If this is a tract home built to be as cheap as possible, then I might consider it (though it would take a lot to make me happy about it).

 

[Ron247]

I think 12" spacing with 1/2" plywood is ok. I have actually walked on one before. It was fairly stiff but I weighed about 50 lbs less at the time. We put 1/2" on roofs spaced at 24" on center all the time. The biggest issue is are you using H-clips at horizontal joints like we do with roofs. Separation at the joints is something I paid no attention to years ago when I walked on that storage mezzanine that had no floor finish on it.

 

[KootK]

This mostly echoes what others here are saying and is pretty typical of what I see in my market for non-sensitive floor finishes: Link. I see a lot of 19.2" spacing for the tract homes in my area.