Floor for wc in garage

[Crakkers]

Building a WC in Garage

My proposal is to raise the floor of the garage to the level of the kitchen via timber joists that rest on the existing concrete floor. The amount of raise is 200mm. I intend to pack in between the joists with jablite or kingspan but I am unsure of exactly how thick this should be. Also I am unsure of the addition of a second DPM. Clearly, the existing floor has a DPM.

1. Do I lay another DPM on the existing concrete floor and build up off that? Or do you advise another solution?

2. How thick should the jablite be? - Pack to the full depth or have an air space below and or above? If so how big an air space.

I intend to have 18mm chip or plyboard plus laminate flooring to finish above the timbers.

Please can you advise?

Thanks in advance

Brian