Raising a floor level

[z1ppy]

Hi all. I have looked through this site numerous times and there appears to be conflicting information on the best route to take on how to raise a floor level.
I have at the moment a flag stone floor on a concrete base that I need to raise approximately 125mm to meet an existing floor level. My thoughts were to lay a damp proof membrane over the flag stones, use 4" x 2" timbers to make a decking, pack out or bedded on concrete to get the right height and level then put 10mm kingspan between the timbers and finish off with 18mm ply. This should then give me a good base to add the wooden flooring.
As the existing floor I am leveling to is suspended I did not want to go down the concrete route as you will get a change in sound as you walk through.
Any recommendations or thoughts would be much appreciated.

 

[gregers]

just a thought,could you not use self leveller.
then make it into a floating floor?

 

[z1ppy]

Hi thanks for the idea, but I wanted to keep the floor hollow so it has the same sound as the existing floor. From other posts I also believe that the concrete or screed needs to be between 75mm and 100mm, which would not allow for insulation.