Adding(additional)Subfloor

[Ronald Thompson]

Have a friend who is replacing a 55 year old T&G 2 1/4" oak floor. Some installers say they need to install at least a 3/8" plywood subfloor on top of the existing 1x6 x 3/4" shiplapped subfloor that is there. The subfloor is in fine condition. They did not ask why it needed to be installed. The floor covers about 500 sq ft. in the living and dining rooms.
Any thoughts?
Ron

[Lloyd McKinlay]

Sounds like he has been talking to Home Depot, they recommend new subfloor for nerly everything.:p

Seriously, if the existing subfloor is in good condition it should be fine. Might not be a bad idea to re-nail it, after 55 years and tearing up the old floor there could be loose boards.

He might check with the manufacturer of his new floor to learn exactly what they recommend.

[Tom Jones III]

I recently installed 3/8" flooring over 3/4" plywood and it went fine. However, my house is fairly new construction with joists set close together. I used deck screws anywhere that I was worried about future squeaks in the plywood. All together I probably spent more time on preparation than I did on laying the new floor.

[Pete Brown]

I recently put down bamboo flooring in my house (the stranded stuff - hard as tile). The manufacturer recommends a minimum thickness of subfloor that was thicker than ours (I forget the exact thickness). My 1979 house had a 5/8" thick subfloor with a lot of squeaks and rough spots.

First, I screwed down some of the squeaky spots and hammered in any protuding nails. We then put down a 5/8" thick T&G fir subfloor over the old one (offset by half a sheet of plywood) and glued and screwed it down with coated deck screws. I wasn't concerned about height as we were replacing all the doors on that floor anyway (including exterior deck door). Typically you'd have to raise or cut the doors for new flooring, so this should not be a real consideration.

Putting down the second layer of subfloor was one of the best things we could have done. The floor feels more solid, has less bounce, almost no squeaks and generally feels better and flatter.

One thing that would be good to do, but I just didn't have time or heart to mess with it is to either sister the joists downstairs or install blocking. I may still do the blocking at some point as there are some parts of the floor that still have more bounce than I would like.

As an aside: if you install tile, you usually need 1"+ of subflooring in place, so just do it once and be done with it.

Pete

[Pete Brown]

I recently installed 3/8" flooring over 3/4" plywood and it went fine. However, my house is fairly new construction with joists set close together. I used deck screws anywhere that I was worried about future squeaks in the plywood. All together I probably spent more time on preparation than I did on laying the new floor.

I definitely spent more time on prep as well.

Except for the kitchen floor mess (http://community.irritatedvowel.com/blogs/pete_browns_blog/archive/2005/10/31/Renovation-Progress-Update.aspx), The single most time-consuming task was pulling up all the carpet pad staples from two generations of carpet. I didn't want metal squeaking under the floor, and I couldn't have the pad bits causing a gap between the two layers of subfloor.

Pete

[Tim Devery]

Ron: Just set all the nails on the existing subfloor. Then screw down the floor, if he is worried about squeeks. I install Hardwood flooring all the time. This is going to be 3/4" thick right?
As long as the subfloor will hold the nails or staples from the installation, it will be fine..

[Ronald Thompson]

Answer to question:
The current subfloor and finish floor are running in the same direction. Which would explain the many gaps in the oak floor. As the subfloor moved, it amplified the oak floor movement. The plywood will isloate the two floors as the homeowner want to keep the floor running in the same direction. Renailing the current subfloor has already been discussed with the flooring contractor. I found it odd that he said he wouldn't know if he would need the plywood until he removed the oak floor when all he had to do was go down the basement and look up at the subfloor to see the orientation.
Told friend to call floor guy and order the 1/2" ply and an extra layer of paper to isloate the two subfloors.
Appreciate the replies. Thanks.
Ron