damping ceiling

I am building a sub ceiling for my studio for isolation purpose. Right now i have a big room that is quite high. There is no one above, but there are neighbours close by. The roof is slanted from 4m to 7m, but has very poor isolation. It's basically a wood roof. There are currently wooden beams (ca. 20cmx30cm) at 3.50m. I want to build a sub ceiling onto these beams. My plan is to have 2 layers of OSB 18mm, 12cm Mineral Wool and then another layer of OSB18mm (if i need it). I read in Philip Newells Book that there are 4 aspects to isolation. Damping is one of them. So i was wondering if i damp the space between the wooden beams and the layer of OSB, i might get some added TL. Does it work that way? I was thinking of adding a layer of 2mm thick fleece onto the wooden beams. If this concept works, is it better to have the OSB layer "floating" on the wooden beams, or should i still put nails in the OSB connecting it to the wooden beams? This would make the ceiling more rigid... which again is an aspect of isolation. :) But i remember reading somewhere, that it is not useful to add a damping layer between 2 drywall layers. I don't remember the reason, but i remember that the result was better to have 2 layers of drywall directly stuck to each other instead of having a dampening layer in between. Is this correct?

My plan is to have 2 layers of OSB 18mm, 12cm Mineral Wool and then another layer of OSB18mm (if i need it).

That would make a three-leaf ceiling! You have two leaves there (one leaf is the 2 layers of OSB, the other is the "another layer of OSB", but you also have the original "basically a wood roof" above you. So that makes three leaves, which potentially REDUCES your isolation in low frequencies. I would suggest using resilient channel on the bottom of your joists, and put your two layers of OSB on that. PLus put mineral wool ABOVE that, in the cavity between it and the original roof. You will need as much thickness mineral wool as you can get in there, but not less than about 15cm

So i was wondering if i damp the space between the wooden beams and the layer of OSB

Damping is what the 15cm of mineral wool does. Decoupling is what the resilient channel does. You need both.

I was thinking of adding a layer of 2mm thick fleece onto the wooden beams.

Not any use.

If this concept works, is it better to have the OSB layer "floating" on the wooden beams,

Yes. That's what the resilient channel is for.

or should i still put nails in the OSB connecting it to the wooden beams?

Resilient channel is metal. You cannot nail it. You have to use screws to attach the OSB to the resilient channel, and you also use screws to attach the resilient channel to the joists.

This would make the ceiling more rigid... which again is an aspect of isolation.

Yes, but at very low frequencies it is a negative aspect! :)

But i remember reading somewhere, that it is not useful to add a damping layer between 2 drywall layers.

IT is VERY useful, but it has to be done with the correct material. It must be done with a visco-elastic material, that acts as a constrained layer damping compound between the layers of sheathing. The best product for that is Green Glue compound, which is NOT glue (despite the name).

i remember that the result was better to have 2 layers of drywall directly stuck to each other instead of having a dampening layer in between. Is this correct?

It is correct if you do not use Green Glue, yes! :) Nothing else works like Green Glue does. If you use Green Glue, then the constrained layer damping it provides is very useful. But "fleece" would be no use, and neither would many other materials. - Stuart -