New subfloor under old oak floorboards?

[Athers1971]

Hi,

Looks like in the room we are working on we may need to repair/replace a beam that is supporting joists etc on the first floor - not a big room, 4.1m x 2.1m.

In doing so we'll obviously be revealing the joists etc and the floorboards above (some of them are 300mm wide). I wondered then, whether we should perhaps be thinking of putting say some OSB down on top of the joists, and then re-laying the old floorboards on top?

My logic is that we will be able to get a more level floor, create some additional soundproofing and separation between the room below and the one above?

Is this a done thing, or should I be looking to re-lay the old boards directly back on the joists?

The intention is to put insulation (sheeps wool or wood fibre) between the joists and then replace the ceiling with wood fibre boards rather than plasterboard.

Thoughts?

PS. We've now removed the old "insulation" that was in the ceiling between the joists, it was like a jumble sale of old dresses and curtains - just a small sample below!

 

[Kearn]

The OSB will add weight, but also a structural diaphragm.

However, I wouldn’t be looking to do this if you’re already able to pop a warm false ceiling below.

Old boards and joists will have found a happy balance of mating in an undulating way. Trying to add a flat smooth layer between, will require significant amounts of packing, shimming, chiselling and swearing… plus you’ll raise the floor height which may cause issues. Especially if you’re trying to gain a level floor, it will obviously be set at the highest current point, which could vary dramatically across the room!