Concrete floor to extension. No hardcore and sand blinding not whacked.

You should consult the construction notes from your architect, or if you are on building notice confirm with your building control. However if you are on chalk you can get away with less hardcore if any, if the ground has been undisturbed, The sand should be wacked / consolidated, but being uber level is not so much of a problem as long as you have the minimum thickness of concrete specified.I assume that they have blinded it with sand as they are installing a DPC at this stage. You should be more concerned that there are no stones or sharp objects that are going to puncture the DPC. Your building control officer should always see the DPC installed before concreting anyway.

Hi If the floor is going to be concrete seletex and screed need to be digging down 420 mm lower from existing old screed or ather existing Flor level. 70mm screed 100 mm seletex 150mm concrete round 100mm hardcore totals 4200 mm The hardcore need to be whacked . If the floor is going to be block and beams You need to flow engineering plans! Just you need round 200mm gap under concrete beams for air vent not need whacked ! I hope the information is helpful for you ! I wish you good luck with your extension Cheers Andrea