Insulation thickness and screed depth over B=B floor

[crispy_wafer]

Bit of a dilemma regarding the depths of insulation and screed depths for my ground floor, I'm looking to start purchasing insulation in dribs and drabs whilst some funds allow.

 

Floor build up is Block and Beam, the door openings and DPC are set on 1 concrete block above this, so approx 225mm I think.  Originally I'd thought/planned on 150mm PIR, then screed.  What sort of screed depth?  60mm?

 

Many thanks

[Mr Punter]

Sand cement screed is 75mm plus, liquid is 40mm plus.

[crispy_wafer]

Cheers,

 

Would the screed be laid upto dpc/door opening level then, or a little below?  This could be a depth of 70mm or so if I go with 150mm insulation.  Planning on liquid screen, I guess there's a point at which screed can be too thick?