I would go with 3/4" solid prefinished flooring, perpendicular to the joists. It will add strength to the structure as well. Mark the joists and try to nail on them as well as between.
Since between both floors have HVAC, expansion and shrinkage is same as other parts of the home.
I would not bother with any additional ply.
Good luck.

FROM THIS POINT ON, IT IS FOR THE FLOORING GUYS.
Like most of you, I have seen and refinished 3/4" floors right on joists- (or sleepers) without any subfloor. Most of them are pine, maybe they meant to be subfloor rather than wood floor, but T&G and no face nailed. The last one I repaired and refinished was long-leaf pine,I never thought there was no subfloor underneath until I dig in.
Of course we don't do it now,only problem installing floors directly to joists without subfloor is monkey balancing between the joist while installing them(sometimes knocking your helper to one floor down:laughing. I always wondered how they did install those floors in second,third floors with no subfloor. I guess the plywood did not exist or just to cut costs.

 

FROM THIS POINT ON, IT IS FOR THE FLOORING GUYS.
Like most of you, I have seen and refinished 3/4" floors right on joists- (or sleepers) without any subfloor. Most of them are pine, maybe they meant to be subfloor rather than wood floor, but T&G and no face nailed. The last one I repaired and refinished was long-leaf pine,I never thought there was no subfloor underneath until I dig in.
Of course we don't do it now,only problem installing floors directly to joists without subfloor is monkey balancing between the joist while installing them(sometimes knocking your helper to one floor down:laughing. I always wondered how they did install those floors in second,third floors with no subfloor. I guess the plywood did not exist or just to cut costs.

Astor, you mean you have not been in Central Austin and most of Tarrytown? The older homes had no subfloors, 2¼Oak, directly over 16" centered dimensional lumber joists. Thing is, it started out life as 33/32 flooring.


If it were my home, I'd lay an additional layer of ½" Laying on a 45º, or staggering it from the layer beneath. No matched seams.

 

My floor reps tell me 5/8 min sub floor. Add 1/4" luan & staple off well, then put down the hardwood. That combo will maintain warranty of most manufacturers.

 

He is telling you fairy tales.
squeaks will be the biggest concern so screw down the subfloor.
the guidelines in the hardwood flooring association handbook which I read years ago does not require any subfloor at all. Consider the Ply to be a convenience for you to stand on while nailing down the new flooring. Make sure you nail to joists as well as in the field. Where did all this nonsense about laying down another layer of plywood underneath hardwood flooring get started? I had a flooring sales guy years ago try to hand me that BS about how it would be stronger. I threw him off the job and showed his boss the flooring association book and had him fired. I also personally lived in a house with 1/2 inch ply subfloor and 3/4 T&G oak flooring. Never a squeak or bounce at all and the floor was 45 years old.

 

No hardwood over 1/2" sub. - too much bounce

1/2" plywood is not suitable as a single layer subfloor regardless of what you cover it with. (With one exception, more on that later.) I will also have to disagree with Pinwheel who thinks just adding some luaun and therefore adds thickness will do the trick. It won't. !/4" ply, especially luaun adds virtually no structural strength.

Since this is an attic storage space, I think it would be safe to install 3/4" solid hardwood across the joists as proposed. Just be careful not to place shorts near each other. I would not recommend 3/4" over 1/2" ply in any other application though.

If you want to do a better job why not install another sheet of min. 1/2" underlayment grade plywood, (or 5/8"), then you should be good for most any type of hardwood, solid or engineered.

Jaz

 

1/2" plywood is not suitable as a single layer subfloor regardless of what you cover it with. (With one exception, more on that later.) I will also have to disagree with Pinwheel who thinks just adding some luaun and therefore adds thickness will do the trick. It won't. !/4" ply, especially luaun adds virtually no structural strength.

Sure it does, just like sandwiching multiple 2 by's together to form a beam adds strength to the first 2 by. I was quoting what holds up under warranty & adding luan holds up under warranty. 2" cleats will go through both the 1/2" ply & the 1/4" luan, thus adding another element of fastening.

Like astor, I've worked on quite a few 100 year old heart pine floors nailed directly to the floor joists & they've stood the test of time. Most of the commercial buildings built at the turn of the century here in the midwest were built just this way, with no subfloor.

 

Btw,these pine floors are not meant to be subfloor as they do not expand under the walls.Diagonal or straight pine subfloors usually installed on the whole floor before placing the walls.
Thanks God for the guy who invented T&G structure:notworthy,it has tremendous strength more than you can imagine.
I still think, no reason to add anything-other than warranty, but is another issue-just get some 3/4" flooring 6-7 pieces engage into each other,place it between 2x4 's 16 each apart and let your fat helper step on it. Minimal bounce if there is.The larger the space, more strength adds up.

 

If I am reading this properly
storage room with lite use
I would find the least expensive 3/4 thing I could find
Without checking right now.
around here would probably be 1x pine
assuming that make sure its been dried
lay it down and face nail it
One trick I do use with this is I use my flooring stapler to bang them tight together even though their is no t and g(Takes a little getting used to)
then face nail
glue if you really want to go crazy
Finish as you wish

 

Here's an engineer's take...

1/2" plywood over joists at 24" OC can support 70 psf live load + 10 psf dead load. This is from APA Wood Construction Guide, Table 29. Typical residential live load is 40 psf. Typical light flooring such as carpet, vinyl, or even hardwood will be less than 10 psf dead load. So your 1/2" plywood can take the load easily. But...

The rub comes with bounciness, a.k.a. deflection. The minimum thickness Sturd-I-Floor you can buy is 5/8", which is good for exactly 40 psf live + 10 psf dead. The controlling factor not being strength but deflection.

So if you don't care about bounciness, you can use your 1/2" and be okay. If you do care, you'll need to beef it up.

To accomplish that beefing, adding a layer of hardwood flooring should do the trick. I'd be careful not to let any hardwood plank joints fall over an unsupported plywood joint, however. Stagger them.

The last thing to consider is whether the floor system can take the additional load. Have you considered that? If the joists are undersized, it won't matter what flooring you use, you'll get bounciness. Here's an article I wrote on that topic: http://www.constructioncalc.com/blog/free-items/bouncy-floors-dangerous/

 

The point of minimal deflection is the reason to specify a minimum sheathing thickness and joist spacing. That is why I say 1/4" plywood is NOT structural and when installed will add virtually no strength or stiffness to a subfloor system. That statement goes double when we're talking about Luaun underlayment since it very soft, doesn't like moisture and is very weak. I believe the most common thickness is 5.5 mm which is under .220 inches thick.

Luaun (can also be spelled luan), is used as side & rear panels of cabinets and as an underlayment under vinyl and other flooring when "cheap" is the criteria. It's not very good as an underlayment because it's so soft, but that makes it easy to work with, so many like to use it. Some sheet vinyl manufacturers do not recommend it under their floors because it dents easily leaving indentations. Some don't recommend it because the oils in the wood can be detrimental to their sheet vinyl flooring.

The only way to make 1/4" useful to stiffen a subfloor is to laminate it to the subfloor using a thin wood glue spread 100%. Of course that would be hard to do and no reason to even try.

Jaz

 

Jaz,
You are right on about 1/4" flooring not being structural. Gluing 1/4" plywood would help but there would still be problems at the unsupported joints underneath because the existing 1/2" plywood is not T&G. So why bother.

If this were a full-time floor, I would not have suggested what I did in my first post because deflection would be too much an issue. However, in an attic, the owner might be okay with some deflection. But that's his call. And he needs to be aware of the problems that deflection might cause with the flooring he puts over it.

 

Thanks for the replies guys.

Tim, I have thought about the structure and that is always a concern for me. That is why I do not want to put down 5/8 or 3/4 t&g ply. and then carpet over that. That would be a lot of weight.

The house has 2x 10's @ 16" o.c. The load carried through or down is fully supported. I will however check everything again to be sure.

Now, would it be better to glue and staple/nail the wood or just staple/nail. I am thinking that glueing will make things more solid. I also agree, 3/4" solid would be very strong, but can you glue it? Don't you have to allow for movement?

Again,
Thank you all!

 

Thanks for the replies guys.

Tim, I have thought about the structure and that is always a concern for me. That is why I do not want to put down 5/8 or 3/4 t&g ply. and then carpet over that. That would be a lot of weight.

The house has 2x 10's @ 16" o.c. The load carried through or down is fully supported. I will however check everything again to be sure.

Now, would it be better to glue and staple or nail the wood or just staple or nail. I am thinking that glueing will make things more solid. I also agree, 3/4" solid would be very strong, but can you glue it? Don't you have to allow for movement?

Again,
Thank you all!

Yes, gluing will be the better option as it will fix the wood. Laminate wood flooring is long-lasting and gorgeous upcoming in a variety of finishes. It is uncomplicated to take care of. Merely dust with a dry swab, wipe with a clammy cloth or mop, and/or vacuum with a soft brush attachment.

 

Baylee,

Sorry, I couldn't disagree more with your suggesting of gluing the underlayment to the subfloor sheathing. It should NOT be done. Why would you? The fasteners will keep it from shifting laterally, right? Some people think that the construction adhesive will secure it from moving up & down. WRONG! Just the opposite will occur.

If you use beads of construction adhesive, which is fairly thick in viscosity, it'll actually create voids where there is no glue, probably a good 95% of the area. These voids cause the underlayment to bounce a tiny bit which over time may cause fastener loosening, squeaks and may damage floor coverings. It won't matter with some coverings, but non the less is contrary to what you want. The only time you glue a subfloor system is when installing the subfloor sheets to the joists.

Jaz

 

I agree 100% with Jazman.:thumbup:

 

Same here.

Install a layer of 1/2" minimum (I would go 5/8")screwed, install 3/4" Oak prefinished (most cost effective) with a pneumatic stapler and be done with it. You're making it more complicated than it needs to be.


p.s. Luan has no use whatsoever in any floor covering assembly. Period. It is trash plain and simple. There are purpose specific underlayments for every type of flooring available. Luan is not an approved substrate for any of them.

 

I might be crazy:laughing: I really haven't read all the replies. Around here the houses built in the 70's 80's with hardwood have 3/8" subfloor with the 3/4" hardwood over that perpendicular to the joists. And some of them, the older ones the oak was laid right over the joists.

My dad was a framer in his younger days. We were just talking about this the other day, he said he always hated the 3/8".

That being said. Since its not a main living area, and also if it was at my own house and not a customers. I would just lay some cheap 3/4" flooring right over the 1/2" plywood.


Dave

 

For the persons who thinks an additional ply is needed, please just think about all the decking all around the country,or ask a decking guy.They do not use subfloor and most of the decking materials are 3/4" thick and most of them even do not have t&g.Never seen a deck bouncing or sagging with 16" joists.

 

I'd just put down 3/4" t&g over rosin paper. What I'd be most worried about is if your 1/2" ply in the attic was put down with construction adhesive. If it wasn't then your floor might squeak quite a bit. That would bother me more than deflection for a lite use room. maybe you could find some 5/4 or 6/4 t&g flooring cheap. That would stiffen the floor up for sure.