Hi all - we're about to install acoustic insulation in our 400mm centres posi joist floor.  But I'm not sure what the best size/product to get.

 

I can get Rockwool RWA45 but only in 600mm wide slabs, is this going to be really wasteful/awkward on 400 centres?  Can a stuff two offcuts next to each other and they'll hold in place, or should I be cutting the slab widthways and laying smaller pieces.  Alternatively I can get Rockwool Flexi in 400mm wide slabs, are these going to be easier?

 

As ever in this self-building game I'm pretty sure I could work this out by trying for a couple of hours, but by that point I'd have ordered a pallet of the wrong material! 🤣

We used APR in the ceilings along with res bar, saved the RWA for the walls.  RWA in the ceilings would have been a ballache...  RWA is fairly rigid so offcuts will hold when pressed against each other, however once you get a row in place I'd recommend you be careful if you try to adjust it's positioning as it'll all move!

Use ISO roll Cut it into three with a sharp hand saw  400 mil rolls before taking the plastic off 

I have a similar question. Our floor to ceiling void is about 300mm. Our warrant grant requires a minimum of 100mm >= 10kg/m2 insulation. 

 

I have some Rockwool 100mm RWA45. Will a single layer of this give us a decent enough result? Somehow my intuition is saying add more!?