if theres no ufh and if the clients willing to pay for it. is to lay a liquid dpm over the screed 2 coats would be advisable with a sprinkling of silica sand over the 2nd cot of lq dpm so the addy adheres to it better.mapie do a realy good lq dpm I get it by courier from my local ctd . if you require more info on lq dpms you can go to the floor layers forum
rule of thumb, 1mm per day per depth of screed, but in this age of culpability always get a relative humidity test done first Gooner. Alan Jackson would be my first port of call as to how to/what instruments to use, to get a relevant reading.