Insulating an old concrete floor

[GraemeHM]

We’re close to finishing our extension now and one of the last jobs is converting the old 1950s built kitchen into a cosy office come spare bedroom. The original floor 3x5M is concrete (with some form of bitumen coating) has always been cold.

 

I am looking for advice and suggestions. My thought was to level the floor with sand, lay down 50mm of PIR insulation then overboard that with chipboard. Then underlay and either carpet or LVT.  Not sure about fixing or not the floor ie the celotex or the chipboard. Would it be wise to have in essence a very thick floating floor.

 

any thoughts or guidance much appreciated.