Our building regs inspector has told us to use the following for out concrete floor
6 inches of hardcore, "then whacker it"
2 inches of sand "then whacker it"
Insulation (we have bought 100mm)
4 inch concrete
3 inches screed. (my husband says this sounds like too much screed though? is 3 inches right?)
You'll need to dig out 20" below FFL and if the BI says 3" screed and you want BR approval thats what you must lay.
Your hardcore should be crushed (no large pieces eg bricks) and it will compress about 20% with the wacker plate but this will depend on how loose it is when tipped.
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