replacing existing floor with new slab - minimum excavation

[Bemak]

Hi All, 

Hoping to kick off a project I posted about here previously at the end of the year. It's been delayed for multiple reasons but hopefully it will get a bit of momentum in the next few months. House is an old 2-storey farmhouse, 140 years old with 600mm thick rubble stone walls. The house is in good shape considering it's rarely used and structurally very sound. I had been mulling over whether to dig out the slab at all as the existing floors are relatively sound. In the end, I've decided to dig out the existing floor as it will allow me to install UFH, a radon sump and membrane, and insulation. 

 

I was talking to a very experienced contractor about it recently as I was concerned about the potential knock-on of digging out the existing floor. He suggested that I keep the excavation to the minimum and suggested a build-up of, 100mm compacted hardcore, blinding, Radon barrier, 150mm insulation, 50mm liquid screen with UFH. 300mm overall. his argument is that the existing subfloor would already be well compacted and that the suggested buildup would minimise the potential of disrupting existing walls. I agree but I just wanted to put it out there to see if anyone has done something similar?