Acoustic insulation of T&G boarded floor


I am about to board out a bedroom floor in a new extension with 7" T&G boards. It is over a living room and I want to cut noise transfer downwards as much as poss. Iv'e put 100mm Rockwool Flexi between the joists (400mm crs), but just wonder whether it is worth putting anything between the boards and the top of the joists to dampen footfall. I could add more Rockwool but I'm not sure if this will affect the footfall noise. Anyone know of an acoustic product which could be cut into strips and laid along the top of the joists? Also will this be practical as the boards will be fixed with 65mm cut flooring brads which may then come loose unless the resilient layer is non compressible.
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AJH wrote:

Here's a couple of insulated floor pics that may give you some ideas - along with one of stud partition insulation:
Floor 1 -
http://i19.tinypic.com/630i0s8.jpg
Floor 2 -
http://i18.tinypic.com/53fbzw9.jpg
Floor 3 -
http://i7.tinypic.com/68cj1a0.jpg (stud partitions)
Brian G
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Great old drawings, the book they came from must be interesting. What I have decided to do now is to put 2 layers of Rockwool Flexi between the joists, I think this will deaden most of the sound as it is pushed tight against the joists. I thought about insulating boards over the top of the joists but then thought that I didn't want to loose that much headroom or start trimming doors etc. Having said that I think it's a very good idea for floating floors, but poss not for mine as the nails would still be a solid route for noise. If it was a separating wall between flats then it would all be done totally different anyway.
many thanks.
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have a look here:
http://www.noisestopsystems.co.uk/floors_sound_proofing.htm
mark
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yep I found the same website, it's got some very useful products there.
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