Creaky floors: alternatives to rock wool?

[Garald]

The attic in the place I've now got has a very creaky floor - to say that one can hear every step while in the floor below is a severe understatement. It's an attic that was made inhabitable by previous owners; part of the problem is that they put a laminate floor on top of wood, apparently badly. We will fix that, but we want to go much further in minimizing noise. (The floor below has what will be my library/piano room!)

 

I was just proposed something that contains rock wool (https://www.fermacell.fr/fr/produits/plaques-de-sol/plaque-de-sol-avec-laine-minerale). However, the attic will consist mainly of bedrooms, and I've been avoiding rock wool overall, in part because it seems fairly clear that it can cause lung injury. (It is not remotely as bad as asbestos, and it may or may not be a carcinogen, but, given that I have a touch of asthma, and that it is a family thing...)

 

What are some alternatives without rock wool, of similar or higher effectiveness? 

 

(We would like to lay actual hardwood on top of the insulation layer.)

[JohnMo]

wood fibre, cellulose, natural wool, recycled plastic wool - but they also contain something nasty when you start looking, to either stop them rotting or insects/rodents out

[Seeoda]

Putting in rockwool or fibre into the void might not have a huge impact on soundproofing. What noise do you have? if you want to stop foot steps, use mass loaded vinyl. 

[JonBATConsult]

If its a creaky floor you have then to prevent this all the floor amd orginal deck has to come up. The joists should be checked for being flat and not moving. I see too many dodgy conversions where ceiling joists have become the structural floor. Once checked, joista shimmed if needed, lay mineral or glass wool between the joists (its an irritant, just wear a dust mask). Use expanding polyurethane glue to put down a new chipboard floor. Use the glue between the board and joist and you will have a very quiet low creak floor. 

[Garald]

Update: the contractor treated the floor in some way and then put in some sort of magical squishy membrane before laying hardwood. Apparently it all works nicely (I last was on site after they started laying flooring but before they finished). Maybe the material used looks familiar?

[Big Jimbo]

That to me looks like a kind of underlay that seems to be made of crumbed rubber. It is often used within the recording industry. Bloody heavy if i remember correctly.

[Garald]

Heavy is good for this purpose, no? Only mass stops lower-frequency noise.