Carpet vs plywood on 705

I was wondering what is the best way of reducing impact sound. Floating 2 layers of green glued plywood on 705 or carpet (method recommended by Rod and others when extreme isolation is not needed). Considering I do not mind having carpet or plywood for the acoustics of the room...

Do not use carpet for your isolation spring. Carpeting varies too much to be dependable as a cushion. Besides, there is no data for this. Use OC 705 or 100kg/m3 rock wool. It is not necessary to use GG. I will have to go dig up the data on IIC ratings of the GG when used in this manner... Use 2 layers of 20mm or 3/4" plywood. Stagger the seams and screw the layers together with 1 5/8" or 42mm screws. Be sure to isolate the edges from contacting the surrounding walls - a cushion of 1/2" or 12mm thick 705 or rock wool around the perimeter will do the trick. Cheers, John

Thanks for the response. I was wondering if you have any pictures of how to "finish" the borders of a floor like that. Since there will be 1/2 inch trims of rockwool, how to I hide that 1/2 inch of rockwool (moldings???) Also, thanks for the info on greenglue. Everyone is putting it everywhere so I was thinking it would be good, but if I can save a little cash, that's perfect. Thanks

Sure, have a look at this jpeg. I hope this helps. Cheers, John

Thanks a lot John! Is it possible to use OSB also? Thanks

Yes, but it is mass and rigidity that is at play here. The plywood structure is 1 1/2 inches thick. The OSB should be at least that thick. You could use T&G sub-flooring OSB which comes in 3/4" thickness. Cheers,