Those with experience, which do you prefer? A single layer of thick tongue and groove plywood OR a double layer of thinner plywood? The second floor will be used primarily as a playroom and storage. The plywood will attach to 8"x3.5" steel purlin (I believe) on 24" centers.)

Consider: noise, deflection, and ease of installation, not price.

Advantech T&G followed by 3/4" plywood T&G. Glued to joists and grooves, fastened with screws. You should never have a squeak or a soft spot, but the 24" spacing might lead to some bounce mid span.

If money isn't a huge concern, might step up to a 7/8" product with the 24" span. I think Advantech goes up to 9/8", but those are probably some heavy sheets.

I would do as much as you could. My second floor is 3/4" tongue and groove. No problem with flex or soft spots, but I have 12" OC floor joists, 16" max depending on where it is in the house.

What sucks is that the original builder used nails and cheap adhesive. So, the adhesive did not hold everywhere, and some boards are 'loose'. They don't squeak, but they do 'clunk' when walked on and they contact the joist. Before I did carpet, I went to all of them as best I could and screwed them down. That helped, but I missed a bunch. Not a big deal, just annoying. Now if I want to fix it, i have to use a special product for carpeting. Doable, but an ass pain.

Long story short....good adhesive...long screws. For 24" joist, yeah, id double up as AggieTaco suggested.

[This message has been edited by BrazosDog02 (edited 7/10/2014 2:16p).]

I was looking at single layer 9/8" plywood, double layer 23/32", double layer 19/32", double layer 15/32", or any combination.

32 sheets of 9/8" looks like about $1400 from Lowes. If I'm playing Nerf basketball or doing plyometrics upstairs, I'd rather not bounce.

I'm just wondering if single layer or double layer is preferred.

Advantech spans:
20" - 19/32
24" - 23/32
32" - 7/8
32" - 1
48" - 1 1/8

Call your local BMC and get a price on the 9/8" Advantech and compare to your T&G plywood. Spans should be about the same, so I'd go with whatever 9/8" product is cheaper, assuming your joists were sized for the dead load.

Double layer just creates more room for fastener errors and squeaks. If you're really concerned, you could use some 2x T&G and park a car up there.

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Double layer just creates more room for fastener errors and squeaks. If you're really concerned, you could use some 2x T&G and park a car up there.

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Thanks! This type of certainty was exactly what I was looking for.

Advantech 1 1/8 subfloor nailed with 3 inch ring shank framing nails with liquid nails on the top of the joists.
https://shop.mccoys.com/building-materials/plywood-mdf-and-osb/p.2074

I have never a subfloor squeak with this product using this method but it is heavy

Single layer is preferred.
The old school way was to deck it with 3/4 inch and then put down roofing felt and then install 1/2 inch running the opposite direction of first layer.

[This message has been edited by Jp76 (edited 7/10/2014 6:55p).]

I will second the 1-1/8" Advantech. Single layer helps prevents future squeaks. Be sure to glue and screw to help with that as well.

How long has that been done? I don't think I've ever seen double layered for second floor decking. Always single 3/4" T&G oriented perpendicular to joists. Interesting.

[This message has been edited by Brazosdog02 (edited 7/10/2014 10:36p).]

It was generally done like this until tongue and groove came out. I can't tell you when this happened because my framing days started in 1996 and we were using tongue and groove then but pretty much every 2 story I have opened up to remodel built between 1970-1990 was done in 2 layers. Before advantech we used 1 1/8 tongue and groove plywood. I believe it was called plytanium and each sheet weighed ~100 lbs. the problem with it was you would have to oil prime it once installed because if it rained before the second story got dried in it would try to separate.

Top Notch 350 or Advantech. Advantech is heavier. Moisture they are the same. Plywood is inferior to OSB

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Advantech 1 1/8 subfloor nailed with 3 inch ring shank framing nails with liquid nails on the top of the joists.
https://shop.mccoys.com/building-materials/plywood-mdf-and-osb/p.2074

I have never a subfloor squeak with this product using this method but it is heavy

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All of this.

Just recently remodeled a church and rebuilt the chancel pretty much exactly this way, with joists on 24" centers. Turned out solid as a rock. 9/8 is probably a tad overkill for 2' centers, but there is absolutely no deflection.

From my experience a thicker,single layer is always better. I've installed wood over the original subfloor in a previous house. I just went through and secured the existing subfloor with screws and never had another squeak.

For my second floor, we used TJIs (basically a 12 in wood I beam) for the joists on 16" centers. For the decking used 3/4" Edge Gold tongue and groove. It is an OSB that is water resistant. Liquid nails on the top of the joists and screwed it down with 2.5" screws.

The TJIs are basically a 2x4 on top and bottom with an OSB between. According to my lumber guy, they are stronger than a 2x12. And I know for a fact they weigh 1/4 as much as comparable 2x12s. I had to span 20 and 24ft and I could pick up and carry 2-3 of the joists. Not so on that length 2x12s.

Since absolutely no one mentioned it: GLUE AND SCREW.

Seriously, its worth mentioning again. Some builders run nail guns and leave it at that.

Thanks for all the input. I feel good moving forward. I just got a quote for 1 1/8" Advantech for $38.95/piece. I plan to take a long lunch to go pick it up with glues and screws. I'll hope to get started this evening.

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I just got a quote for 1 1/8" Advantech for $38.95/piece.

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Seems like a really good price, I think I paid over $50 per sheet.

I just got it delivered. My receipt says AdvanTech, the guy I bought it from called it AdvanTech, but they sent Top Notch 350. It looks like $38.95 is still a great price, but should I go to the effort of sending it back?

I was going to start installation tonight.

I have no personal experience with the LP Topnotch sub floor, but I think there is a consensus that Advantech is the better product. I would talk with your supplier.

Advantech is denser and superior 300 day no sand vs 100 day no sand warranty with top notch 350. Moisture it's comparable. It's a price play more than anything.