Rockwool RW3 between joists sufficient heat insulation?

[pls1]

Just started a project to pull down several old ceilings (lath & plaster) in a Victorian house and insulate due to sound problems from the flat above. See pic.
I'm using 100mm slabs of Rockwool RW3 which has a Lambda value (Thermal conductivity) of 0.034 W/mK which is good.
Most of the areas between the joists have the wooden floor of the flat above so no real point of adding more insulation . Around the edges of all the rooms however is open to the eaves above. In these areas I'm considering adding more insulation over the top of the joists as I gather the current recommendation is 270mm thickness.

Is it worthwhile given the good lambda value of the RW3?

 

[Tigercubrider]

I would also see if you could fit RW3 to the vertical wall that I assume is present where the floor stops.
If the wall is simple plasterboard or single skin brick, it may allow sound to enter the void.

friends of mine had a chalet style house and could hear their neighbours in the garden while lying in bed. They had an uninsulated short wall under a sloping ceiling on each side of the bedroom. I helped insulate the crawl space so that the crawl space wall was insulated, and then the crawl floor.
it vastly decreased the noise issue.

 

[pls1]

Interesting point, didn’t consider insulating that. The flat above is currently being sold & is empty, maybe I should get the new buyer to pay for it seeing as it would benefit them & keep their flat warmer!
Question remains though whether to add some cheap fibreglass roll (e.g. 170mm) on top of the RW3 given the good Lambda value of the RW3.
Better photo attached

 

[Deleted member 174758]

Just a minor point, but fibre glass is nowhere near as good a sound insulator as mineral wool

 

[KenGMac]

For sound insulation I have specified some of the products made by Quietex they manufacture a load of good stuff.

in general terms for sound insulation you need "mass" the Georgians and Victorians used deafening, which was ash from fires placed between the joists. and contained by any scrap timber resting on timber bearers nailed to the joists.

Ken

 

[wwwebber]

Just bought some 100mm RW3 myself. Pulling spare room floor up in our spare room upstairs for some electrical work and I thought I might as well do this at the same time. We also intend to expose the floor boards by getting rid of carpet etc so want to avoid sound and heat transmission. After some investigation - this stuff is great and will help a lot.

 

[endecotp]

I'm using 100mm slabs of Rockwool RW3 which has a Lambda value (Thermal conductivity) of 0.034 W/mK which is good.

It’s standard for “wool”-type insulation. Not especially good.

In these areas I'm considering adding more insulation over the top of the joists as I gather the current recommendation is 270mm thickness.

Yes, go for it; you won’t be opening that space up again for a few decades so do what you can now. Put a load of “cheapo” loft roll over the joists. It won’t cost much or take much time.