Overdoing subfloor when prepping for new carpet?

[Greeny12m]

Hi folks,
We're getting new carpet fitted upstairs and I thought I would take the opportunity to try and fix some squeaky floorboards by screwing them down. I removed the carpet in one room and the carpet sales person suggested replacing the hardboard that was there before the carpet was fitted. (Admittedly it seems to have been there since the 60's judging by some newspaper we found). I'm a big one for doing things right and making them last so I thought I would go one better and get some 3.6mm ply and screw it down.
As I was hammering down all the remaining staples from the hardboard I noticed that a lot of the floorboard nails went in a little bit further if I have them a whack... So my question is this: do I risk squeaks in the future if I only secure the current squeaky ones then screw the ply onto the floorboards? Or should I add a screw or 2 at every nailing point? Further to that, am I right doing 150mm spacing on the ply and should I leave a 1mm gap between ply sheets so they cannot rub together?

Thanks in advance!

 

[Deleted member 174758]

When nailing down overboarding I'd normally do so on 100mm centres -150mm centres is what is used for screws (with 100mm centres around the board edges). I doubt you'll need to spend forever going round punching nails under, though. By all means punch under the loose/raised ones, but only add extra screws if the biardcis still loose (being careful to check that you aren't screwing into a wire or pipe first). What you are possibly dealing with is the result of shrinkage of the floorboards over time (perhaps due to central heating, which the house didn't originally have?). Once the timber has reached equilibrium with the environment it was installed into it will generally not shrink any further (climate change permitting). Also don't bother with a 1mm gap between sheets - it won't achieve anything because any creaking is going to come from loose boards beneath the ply (which you've already said you are dealing with)