# New subfloor over old subfloor



## mae-ling (Dec 9, 2011)

- It was laid diagonally to angle brace the floor, that was common in some areas. Also could then lay hardwood either way.
- why go with 5/8" t&G you do not need the strength. I would use a underlay like proboard or whatever is common in you area. usually 1/4 to 5/16 inch thick.
we use adhesive in a caulking tube and staples that each leg is cut on opposite angles so the legs do the splits as they go in. you can also use ring shank nails. Make sure the heads are just below the surface.


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## joecaption (Nov 30, 2011)

The second layer is under layment, not subflooring.
It's never attached to the joist!
Main reason is to have direct contact to the subfloor below.
There's always small gaps between the floor joist.
No way would I use screws, screws are much more expencive, labor intensive, and leaves humps from compressing the wood. 8D ring shanked nails will work.
I'd be using Advantec not reguler OSB.


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## mae-ling (Dec 9, 2011)

Screw the existing 'plank' to the floor joists before you put down a underlayment.


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## ront02769 (Nov 28, 2008)

I would also use advantech but would glue and screw 100%. Ron


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## joecaption (Nov 30, 2011)

Underlayment is never glued down!!!
Use screws and there's going to be humps every few inches.


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## mae-ling (Dec 9, 2011)

Joecaption - must be a regional thing, proboard and the like is always glues and nailed/stapled here.


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## GeneyLI (Feb 27, 2015)

The older subfloor is showing it's age. There are 1/8 to 1/4 inch spacing between the planks. Also, some of the plank ends are either partially or completely off the joists which has already led to some of them cracking or pieces breaking completely off. One room even showed some fire damage (previous owner was a big smoker). Popped out knots have made more holes and weakened the boards neve more. Finally, we have heavy cast iron radiators which is also why we opted for the thicker OSB. FYI, we have already purchased and received the OSB so can't switch to Advantech but will keep it in mind for future projects.
We also invested in an automatic screw gun which does both framing and drywall. Costs more money for collated screws but after trying it out it would take less than half the time it would to screw with a drill or impact driver. And we are going to use Liquid Nails subfloor adhesive both to hold down the OSB and fill in the larger gaps between the old subfloor planks.
As for the main question, wouldn't the fastening pattern for the OSB put screws in both the joists and older subfloor? I just want to make sure wether or not I can do that or avoid the joists entirely.


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## seephor (Mar 9, 2014)

My home built in the early 60's had the same plank subfloor with oak hardwood on top. I initially thought I would just remove the oak and install my new floor on the old subfloor but after removing the oak, I noticed the subfloor was too deteriorated, lots of cracks, some areas had 1/4 of joints and it had this old moisture moldy smell to them. I just couldn't install the new plywood over this stuff so I cut around the walls and ripped it out a section at a time. It was hard work but I'm glad I did because it gave me a chance to refasten the floor joists that were loose, I also found a small section of floor joists that had past termite damage so I replaced those. It also opened up the floor to replace the old cast iron drain pipes and replace with ABS, I installed insulation since there was none before, I installed blocking the strengthen the floor, ripped out 55 years worth of old cable/phone wires, cleaned up the trash that had accumulated and found LIVE electrical wires that were just wire nutted off and left on the BARE ground :/

It was a lot of work but I'm glad I did it. I went with 3/4 TnG plywood with the glue/screw system. Since I did the work myself, I just paid for the plywood which came out to roughly $1500 and hauling the old floor and subfloor another $300. If I were to contract this out, I'm looking at 10K easily and it would be difficult to do the other stuff I did while the subfloor was removed...

Msg me for tips and tricks I learned along the way if you'd like if you want to go this route. Good luck


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